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2015 publications citing ADF
First author: Banerjee, S, Understanding the ring-opening, chelation and non-chelation reactionsg between nedaplatin and thiosulfate: a DFT study based on NBO, ETS-NOCVg and QTAIM, THEORETICAL CHEMISTRY ACCOUNTS, 135, , (2015)
Abstract: The current work investigates a DFT-based in silico study on the mechanism of reaction between the anticancer drug nedaplatin [Pt(NH3)(2)(Gly-kappa O-2,O')] (Gly = -OCCH2COO-) and the rescue agent thiosulfate (S2O3 (2-)) in molar ratios 1:1 and 1:2, in neutral- and proton-assisted pathways. The first step produces stable (kappa S or kappa O) intermediates via ring opening of Gly. The second, rate-limiting step consists of three competing reactions: (1) kappa S-2,O-chelate formation by S2O3 (2-) or HS2O3 (-) (2) Pt-bis(thiosulfate) formation by the elimination of Gly ligand and (3) Pt-bis(thiosulfate) formation by the elimination of one NH3 trans to sulfur owing to strong trans-labilizing thiosulfate ligand. Results show that non-chelation reaction involving uptake of the second thiosulfate is kinetically more favorable than the corresponding kappa S-2,O-chelate formation. Further, the kinetic barrier of NH3 loss reaction is found to be very close to that of Gly loss. However, in solution phase, the ammine loss reaction is slower than the glycolate loss. The possibility of the formation of four-membered binuclear mu-thiosulfate bridge [Pt-2(mu-S2O3)(2)(NH3)(4)] has also been considered. The proposed reaction paths have been substantiated through computation of structural, thermodynamic and kinetic parameters involved in the gas and solution phase, and also by topological analysis based on quantum theory of atoms in molecules of Bader and the ETS-NOCV energy decomposition scheme.
First author: Palacios, A, Theoretical methods for attosecond electron and nuclear dynamics:g applications to the H-2 molecule, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 48, , (2015)
Abstract: Attosecond science, born at the beginning of this century with the generation of the first bursts of light with durations shorter than a femtosecond, has opened the way to look at electron dynamics in atoms and molecules at its natural timescale. Thus controlling chemical reactions at the electronic level or obtaining time-resolved images of the electronic motion has become a goal for many physics and chemistry laboratories all over the world. The new experimental capabilities have spurred the development of sophisticated theoretical methods that can accurately predict phenomena occurring in the sub-fs timescale. This review provides an overview of the capabilities of existing theoretical tools to describe electron and nuclear dynamics resulting from the interaction of femto- and attosecond UV/XUV radiation with simple molecular targets. We describe one of these methods in more detail, the time-dependent Feshbach close-coupling (TDFCC) formalism, which has been used successfully over the years to investigate various attosecond phenomena in the hydrogen molecule and can easily be extended to other diatomics. In addition to describing the details of the method and discussing its advantages and limitations, we also provide examples of the new physics that one can learn by applying it to different problems: from the study of the autoionization decay that follows attosecond UV excitation to the imaging of the coupled electron and nuclear dynamics in H-2 using different UV-pump/IR-probe and UV-pump/UV-probe schemes.
First author: Sahoo, S, Conceptual Basis for Understanding C-C Bond Activation in Ethane byg Second Row Transition Metal Carbides, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 12855, (2015)
Abstract: It has been suggested that the addition of carbon to Mo and W may improve their catalytic properties and even grant these metal carbides behaviors similar to those of late transition metals such as Pd and Pt. First-principles studies on the C-C bond activation of ethane by 4d transition metal (TM) atoms and TMC molecules have been carried out to develop a conceptual model underlying the changes. We find that the addition of carbon to TM atoms leads to large variations in the activation barrier depending on the metal, and that MoC indeed reveals a pronounced reduction in the C-C bond activation energy. A critical examination of molecular orbitals shows that the changes in reactivity are not linked to a dramatic increase in the filling of 4d states as implied by the analogy with Pd. The reactivity is governed by the location and filling of the Ss and 4d orbitals, with the different orbitals controlling different facets of reactivity. The Ss state controls the initial binding of ethane, with a strong anticorrelation between the ethane binding energy and the Ss occupation, while the location of the 4d(z)(2) orbital controls the reaction barrier that controls the activation energy for cleaving the C-C bond.
First author: Andrada, DM, Direct estimate of the internal Pi-donation to the carbene centre withing N-heterocyclic carbenes and related molecules, BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY, 11, 2727, (2015)
Abstract: Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X -> p(pi) pi-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X -> p(pi) pi-donation while mesoionic carbenes possess the strongest pi-donation.
First author: Smith, CE, Length-Dependent Nanotransport and Charge Hopping Bottlenecks in Longg Thiophene-Containing pi-Conjugated Molecular Wires, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 15732, (2015)
Abstract: Self-assembled conjugated Molecular wires containing thiophene up to 6 nm in length were grown layer-by-layer using click chemistry. Reflection-absorption infrared spectroscopy, ellipsometry and X-ray photoelectron spectroscopy were used to follow the stepwise growth. The electronic structure of the conjugated wires was Studied with cyclic voltammetry and UV-vis spectroscopy as well as computationally with density functional theory (DFT). The current-voltage curves (+/-1 V) of the conjugated molecular wires were measured with conducting probe atomic force microscopy (CP-AFM) in which the molecular wire film bound to a gold substrate was contacted with a conductive AFM probe. By systematically measuring the low bias junction resistance as a function of length for molecules 1-4 urn long, we extracted the structure dependent tunneling attenuation factor (beta) of 3.4 nm(-1) and a contact resistance of 220 k Omega. The crossover from tunneling to hopping transport was observed at a molecular length of 4-5 nm with an activation energy of 0.35 eV extracted from Arrhenius plots of resistance versus temperature. DFT calculations revealed localizations of spin densities (polarons) on molecular wire radical cations. The calculations were employed to gauge transition state energies for hopping of polarons along wire segments. Individual estimated transition state energies Were 0.2-0.4 eV, in good agreement with the experimental activation energy. The transition states correspond to flattening of dihedral angles about specific imine bonds. These results open up possibilities to further explore the influence of molecular architecture on hopping transport in molecular junctions, and highlight the utility of DFT to understand charge localization and associated hopping-based transport.
First author: Vishnevskiy, YV, Influence of Antipodally Coupled Iodine and Carbon Atoms on the Cageg Structure of 9,12-I-2-closo-1,2-C2B10H10: An Electron Diffraction andg Computational Study, INORGANIC CHEMISTRY, 54, 11868, (2015)
Abstract: Because of the comparable electron scattering abilities of carbon and boron, the electron diffraction structure of the C-2v-syrnmetric molecule closo-1,2-C2B10H12 (1), one of the building blocks of boron cluster chemistry, is not as accurate as it could be. On that basis, we have prepared the known diiodo derivative of 1, 9,12-I-2-closo-1,2-C2B10H10 (2), which has the same point-group symmetry as 1:but in which the presence of iodine atoms, with their much stronger ability to scatter electrons, ensures much better structural characterization of the C2B10 icosahedral core. Fur-them-lore, the influence on the C2B10 geometry in 2 of the antipodally positioned iodine substituents with respect to both carbon atoms has been examined using the concerted application of gas electron diffraction and quantum chemical calculations at the MP 2 and density functional theory (DFT) levels. The experimental and computed molecular geometries are in good overall agreement. Molecular dynamics simulations used to obtain vibrational parameters, which are needed for analyzing the electron diffraction data, have been performed for the first time for this class of compound. According to DFT calculations at the ZORA-SO/BP86 level, the B-11 chemical shifts of the boron atoms to which the iodine substituents are bonded are dominated by spin orbit coupling. Magnetically induced currents within 2 have been calculated and compared to those for [B12H12](2-)) the latter adopting a regular icosahedral structure with I-h point-group symmetry. Similar total current strengths are found but with a certain anisotropy, suggesting that spherical aromaticity is present; electron delocalization in the plane of the hetero atoms in 2 is slightly hindered compared to that for [B12H12](2-), presumably because of the departure from ideal icosahedral symmetry.
First author: Alain, AE, B-11 Solid-State NMR Interaction Tensors of Linear Two-Coordinate Boron:g The Dimesitylborinium Cation, INORGANIC CHEMISTRY, 54, 11889, (2015)
Abstract: Borinium cations (R2B+) are of particular fundamental and applied interest in part due to their pronounced Lewis acidity which enables unique chemical transformations. Solid-state NMR spectroscopy of magic-angle spinning and stationary powdered samples of the dicoordinate boron cation in the recently reported dimesitylborinium tetrakis(pentafluorophenyl)borate compound (Shoji et al. Nature Chem. 2014, 6, 498) is applied to characterize the B-11 electric field gradient (EFG) and chemical shift (CS) tensors. The experimental data are consistent with linear C-B+-C geometry. The B-11 quadrupolar coupling constant, 5.44 ± 0.08 MHz, and the span of the CS tensor, 130 ± 1 ppm, are both particularly large relative to literature data for a variety of boron functional groups, and represent the first such data for the linear C-B+-C borinium moiety. The NMR data are similar to those for the neutral tricoordinate analogue, trimesitylborane, but contrast with those of the Cp-2*B+ cation. Quantum chemical calculations are applied to provide additional insights into the relationship between the NMR observables and the molecular and electronic structure of the dimesitylborinium cation.
First author: Binding, SC, Synthesis, Structure, and Bonding for Bis(permethylpentalene)diiron, INORGANIC CHEMISTRY, 54, 11935, (2015)
Abstract: The synthesis of the first homoleptic double metallocene complex of iron, Fe(2)Pn(2)* (Pn* = permethylpentalene, C8Me6) is described. The structural and electronic properties of Fe(2)Pn(2)* have been characterized by NMR and EPR spectroscopy, single crystal X-ray diffraction, magnetic measurements, cyclic voltammetry, and DFT calculations. Fe(2)Pn(2)* adopts a C-i symmetry in the solid state with a Fe-Fe distance of 2.3175(9) angstrom, slightly lower than the sum of radii in metallic iron. Magnetic measurements in solution, and of the solid phase between 60 and 300 K, indicate that Fe(2)Pn(2)* is a triplet (S = 1) paramagnet, with effective magnetic moments (mu(eff)) of 3.4 and 3.48 mu(B), respectively. DFT calculations indicate the origin of this high magnetic moment is likely to be unquenched orbital angular momentum contributions from two SOMOs which have metal d character. Cyclic voltammetry studies demonstrate that Fe(2)Pn(2)* can access four charge states (-1, 0, +1, +2).
First author: Caramori, GF, Ruthenium nitrosyl complexes containing pyridine-functionalized carbenesg – A theoretical insight, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 799-800, 54, (2015)
Abstract: The Ru NO bonding situation in a set of ruthenium(II) nitrosyl complexes containing pyridinefunctionalized carbenes as bidentate ligands is presented. Cheng's complex [(L)Ru(NO)Cl-3], where L = 3-tert-butyl-1-(2-pyridyl)imidazol-2-ylidene, la, was used as a model structure and the effect of different families of pyridine-functionalized carbene ligands on the Ru NO bond strength was explored, including imidazolylidenes, triazolylidenes, oxazolylidenes, thiazolylidenes, P-heterocyclic carbenes, imidazolidinone, triazolidinone, among others. The results reveal that the NO group binds more strongly to the Ru(II), than carbene carbon or pyridine nitrogen atoms. The EDA-NOCV results show that the nature of the carbene has a direct influence on the lability of the Ru NO, since it changes the electronic environment around the metallic centre. EDA-NOCV results point out that the nature of the Ru NO interactions (1a-16b) presents a very preponderant covalent character (circa 70%), while the electrostatic character covers circa 30% of the total interaction energy. The energy decomposition still reveals that Ru-NO+ bonds are strengthen in complexes la-16a, than in lb-16c. The weakest Ru NO interactions are observed for complexes containing P-heterocyclic ligands (PHCs), specially for complexes where the NO is coordinated trans to the carbene carbon atoms. The metal, ligand r-back-donation is more intense towards PHC than towards NO+.
First author: Casella, G, Four-Component Relativistic DFT Calculations of C-13 Chemical Shifts ofg Halogenated Natural Substances, CHEMISTRY-A EUROPEAN JOURNAL, 21, 18834, (2015)
Abstract: We have calculated the C-13 NMR chemical shifts of a large ensemble of halogenated organic molecules (81 molecules for a total of 250 experimental C-13 NMR data at four different levels of theory), ranging from small rigid organic compounds, used to benchmark the performance of various levels of theory, to natural substances of marine origin with conformational degrees of freedom. Carbon atoms bonded to heavy halogen atoms, particularly bromine and iodine, are known to be rather challenging when it comes to the prediction of their chemical shifts by quantum methods, due to relativistic effects. In this paper, we have applied the state-of-the-art four-component relativistic density functional theory for the prediction of such NMR properties and compared the performance with two-component and nonrelativistic methods. Our results highlight the necessity to include relativistic corrections within a four-component description for the most accurate prediction of the NMR properties of halogenated organic substances.
First author: Liu, RY, Tris(beta-diketonato)chromium(III) complexes: Effect of theg beta-diketonate ligand on the redox properties, ELECTROCHIMICA ACTA, 185, 288, (2015)
Abstract: A combined quantum chemistry and electrochemistry study of a series of tris(beta-diketonato)-Cr(III) complexes showed that the different electron donating properties of the R and R' groups, substituted on the 1 and 3 positions of the beta-diketonate ligand (RCOCHCOR'), largely influence the redox properties of these complexes, due to the good communication between the R and R' groups and the metal via the beta-diketonato-metal conjugated system. Linear relationships were obtained between the reduction potential of the tris(beta-diketonato)-Cr(III) complexes and a variety of electronic parameters used to describe the electron-donating and -withdrawing power of the R and R' groups on the beta-diketonate ligand.
First author: Faucher, A, Solid-State Sr-87 NMR Spectroscopy at Natural Abundance and Highg Magnetic Field Strength, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 11847, (2015)
Abstract: Twenty-five strontium-containing solids were characterized via Sr-87 NMR spectroscopy at natural abundance and high magnetic field strength (B-0 = 21.14 T). Strontium nuclear quadrupole coupling constants in these compounds are sensitive to the strontium site symmetry and range from 0 to 50.5 MHz. An experimental Sr-87 chemical shift scale is proposed, and available data indicate a chemical shift range of approximately 550 ppm, from -200 to +350 ppm relative to Sr2+(aq). In general, magnetic shielding increased with strontium coordination number. Experimentally measured chemical shift anisotropy is reported for stationary samples of solid powdered SrCl2 center dot 6H(2)O, SrBr2 center dot 6H(2)O, and SrCO3, with delta(aniso)(Sr-87) values of +28, +26, and -65 ppm, respectively. NMR parameters were calculated using CASTE?, a gauge including projector augmented wave (GIPAW) DFT-based program, which addresses the periodic nature of solids using plane-wave basis sets. Calculated NMR parameters are in good agreement with those measured.
First author: Lai, CT, Light-Driven Ca2+ Ion Pump: How Does It Work?, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 15110, (2015)
Abstract: Work done by Bennett et al. [Nature 2002, 420, 398-401] demonstrated that Ca2+ ions can be actively transported through a lipid bilayer membrane by an artificial photosynthetic machine. However, details of the pump process, such as the oxidation state of the shuttle molecule and stoichiometry of the shuttle-ion complex, are not fully understood, which hinders the development of ion pumps of this type with higher efficiency. In this study, we combine all atom molecular dynamics simulations and quantum mechanics calculations to estimate the time scale of the shuttle-ion complex diffusion process and charge transfer step. We find that the process of shuttle-ion complex diffusion across the lipid bilayer membrane is the rate-limiting step, with a time scale of seconds to minutes. Other processes such as charge transfer between the redox reaction center and the shuttle molecule have picoseconds time scales. We also show that a shuttle-ion complex with 2:1 stoichiometry ratio has a lower energy barrier across the lipid membrane than other choices of complexes. The calculations show that the Ca2+ ion is likely to be shuttled by a semiquinone type of shuttle molecule as this has the lowest free energy barrier across the lipid bilayer membrane, the fewest electrons transferred in the redox cycle, and it does not generate (or require) proton flow. Estimates of ion flow rates are consistent with measured values.
First author: Knoppe, S, Nonlinear Optical Properties of Thiolate-Protected Gold Clusters: Ag Theoretical Survey of the First Hyperpolarizabilities, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 27676, (2015)
Abstract: A series of thiolate-protected gold clusters has been successfully crystallized in recent years, and on the basis of these crystal structures, we investigate the static first hyperpolarizabilities beta(0) of eight model clusters [Au-m(SH)(n)](z) (m = 18-38) by means of density-functional theory. We used simplified ligands -SH, which may lead to higher symmetries than in actual systems (e.g., with -SCH2CH2Ph or -SPh ligands). A dependence of the obtained values on the exchange-correlation functional during geometry optimization was found. No correlation between cluster size and beta(0) was identified. Instead, the symmetry of the clusters seems to dominate the NLO properties. Our survey predicts strong NLO responses in the chiral Au-38(SR)(24) cluster, whereas centrosymmetric structures such as the [Au-25(SR)(18))] yield hyperpolarizabilities close to zero. This is in line with recent experimental results obtained by second-harmonic generation. The centrosymmetry of the Au-25 cluster is efficiently destroyed by ligand exchange, as demonstrated by the inclusion of chiral, bidentate ligands (1,1′-binaphthyl-2,2′-dithiol, 1,1′-biphenyl-2,2′-dithiol) and two thiophenolate ligands. This induces significant hyperpolarizabilities, surpassing those of intrinsically chiral clusters (e.g., Au-38(SH)(24)). Our results are of significance for the use of monolayer-protected noble metal clusters as contrast agents in NLO imaging applications.
First author: Zhang, WW, ReaxFF Reactive Molecular Dynamics Simulation of Functionalizedg Poly(phenylene oxide) Anion Exchange Membrane, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 27727, (2015)
Abstract: Three functionalized poly(phenylene oxide) (PPO) anion exchange membranes (AEMs), PPO-trimethylamine (PPO-TMA), PPO-dimethylbutylamine (PPO-DMBA), and PPO-dimethyloctylamine (PPO-DMOA), at two hydration levels (lambda = 8.3 and 20.8) have been studied by ReaxFF reactive molecular dynamics simulations. Our simulations reveal that with increasing hydration the microstructures of membrane swell and water molecules are more likely to form a channel, which improves the diffusion of hydroxide ion (OH-). Our study of OH- diffusion demonstrates that PPO-TMA hydrated membrane provides the biggest diffusion constant at the high hydration level. However, from comparison of the structural and dynamical properties of the three membranes at the same water content, it is found that when one methyl group of quaternary ammonium center is replaced by a long alkyl chain group, the hydrophobic effects block the OH- approaching nitrogen, resulting in a lower rate of degradation and an improved alkaline stability of PPO-DMOA hydrated membrane. On the basis of these simulation results, we expect that a high performance AEM fuel cell should balance the conductivity with stability of the membrane.
First author: Pinter, B, Cyclo-P-3 Complexes of Vanadium: Redox Properties and Origin of the P-31g NMR Chemical Shift, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 15247, (2015)
Abstract: The synthesis and characterization of two high-valent vanadium-cyclo-P-3 complexes, (nacnac)V(cyclo-P-3) (Ntolyl(2)) (1) and (nacnac)V(cyclo-P-3) (OAr) (2), and an inverted sandwich derivative, [(nacnac)V(Ntolyl(2))](2)(mu(2)-eta(3):eta(2)-cyclo-P-3) (3), are presented. These novel complexes are prepared by activating white phosphorus (P-4) with three-coordinate vanadium(II) precursors. Structural metrics, redox behavior, and DFT electronic structure analysis indicate that a [cyclo-P-3](3-) ligand is bound to a V(V) center in monomeric species 1 and 2. A salient feature of these new cyclo-P-3 complexes is their significantly downfield shifted (by similar to 300 ppm) P-31 NMR resonances, which is highly unusual compared to related complexes such as (Ar[Pr-i]N)(3)Mo(cyclo-P-3) (4) and other cyclo-P-3 complexes that display significantly upfield shifted resonances. This NMR spectroscopic signature was thus far thought to be a diagnostic property for the cyclo-P-3 ligand related to its acute endocyclic angle. Using DFT calculations, we scrutinized and conceptualized the origin of the unusual chemical shifts seen in this new class of complexes. Our analysis provides an intuitive rational paradigm for understanding the experimental P-31 NMR spectroscopic signature by relating the nuclear magnetic shielding with the electronic structure of the molecule, especially with the characteristics of metal-cyclo-P-3 bonding.
First author: Thornley, WA, Intramolecular C-H Activation and Metallacycle Aromaticity in theg Photochemistry of [FeFe]-Hydrogenase Model Compounds in Low-Temperatureg Frozen Matrices, CHEMISTRY-A EUROPEAN JOURNAL, 21, 18218, (2015)
Abstract: The [FeFe]-hydrogenase model complexes [(mu-pdt){Fe(CO)(3)}(2)], [(mu-edt){Fe(CO)(3)}(2)], and [(mu-mdt){Fe(CO)(3)}(2)], where pdt=1,3-propanedithiolate, edt=1,2-ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time-resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl-loss species. Apical carbonyl-loss isomers are also generated and may undergo secondary photolysis, resulting in beta-hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers. For [(mu-bdt){Fe(CO)(3)}(2)], (bdt=1,2-benzenedithiolate), apical photodecarbonylation results in generation of a 10 pi-electron aromatic FeS2C6H4 metallacycle that coordinates the remaining iron through an eta(5) mode.
First author: Li, WL, Periodicity, Electronic Structures, and Bonding of Gold Tetrahalidesg [AuX4](-) (X = F, CI, Br, I, At, Uus), INORGANIC CHEMISTRY, 54, 11157, (2015)
Abstract: Systematic theoretical and experimental investigations have been performed to understand the periodicity, electronic structures, and bonding of gold halides using tetrahalide [AuX4](-) anions (X = F, Cl, Br, I, At, Uus). The [AuX4](-) (X = Cl, Br, I) anions were experimentally produced in the gas phase, and their negative-ion photoelectron spectra were obtained, exhibiting rich and well-resolved spectral peaks. As expected, Au-X bonds in such series contain generally increasing covalency when halogen ligands become heavier. We calculated the adiabatic electron detachment energies as well as vertical electron detachment energies using density functional theory methods with scalar relativistic and spin orbit coupling effects. The computationally simulated photoelectron spectra are in good agreement with the experimental ones. Our results show that the trivalent Au-III oxidation state becomes progressively less stable while Au-I tends to be preferred when the halides become heavier along the Periodic Table. This series of molecules provides an example for manipulating the oxidation state of metals in complexes through ligand design.
First author: Thomassen, IK, Octaiodoporphyrin, INORGANIC CHEMISTRY, 54, 11493, (2015)
Abstract: Interaction of 3,4-diiodopyrrole with 4-trifluoromethylbenzaldeyde under carefully optimized, Lindsey-type conditions at -10 degrees C has led to the synthesis of the first beta-octaiodoporphyrin, H-2[I(8)TpCF(3)PP]. The free ligand readily yielded Ni, Cu, and Zn complexes, which all proved amenable to single-crystal X-ray structure analyses. The zinc complex Zn[I8TpCF3PP] exhibits the most saddled porphyrin core for any simple porphyrin known to date and a dramatically red-shifted optical spectrum with a Soret maximum at 495 nm.
First author: Gong, Y, Electrospray production and collisional dissociation ofg lanthanide/methylsulfonyl anion complexes: Sulfur dioxide anion as ag ligand, INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 392, 45, (2015)
Abstract: Gas-phase lanthanide-SO2 complexes, Ln(CH3SO2)(3)(SO2)(-), were produced by collision induced dissociation (CID) of Ln(CH3SO2)(4)(-) precursors prepared by electrospray ionization. For all lanthanides except Eu, CID of Ln(CH3SO2)(4)(-) resulted in CH3 loss to form Ln(CH3SO2)(3)(SO2)(-), which spontaneously react with O-2 to form Ln(CH3SO2)(3)(O-2)(-). CID of Eu(CH3SO2)(4)(-) produced only Eu(CH3SO2)(3)(-), with reduction from Eu(III) to Eu(II). For Ln =Yb and Sm, the Ln(CH3SO2)(4)(-) underwent neutral ligand loss to form Ln(CH3SO2)(3)(-), which reacted with O-2 to yield Ln(CH3SO2)(3)(O-2)(-), recovering the Ln(III) oxidation state. The CID results show parallels to condensed-phase Ln(3+)/Ln(2+) redox chemistry. Density functional theory (DFT) calculations on Ln(CH3SO2)(3)(SO2)- for Ln=La, Yb and Lu reveal that SO2 acts as a bidentate oxygen bound ligand for doublet ground-state La(CH3SO2)(3)(SO2)(-) and Lu(CH3SO2)(3)(SO2)(-), while the ground state for Yb(CH3SO2)(3)(SO2)- is an open-shell singlet with a monodentate SO2 ligand. Loss of CH3 is computed to be much more favorable than neutral ligand loss for La(CH3SO2)(4)(-) and Lu(CH3SO2)(4)(-), whereas both channels are comparable in energy for Yb(CH3SO2)(4)(-), in accord with the experiments. DFT results for fragmentation of Cu(CH3SO2)(2)(-) reveal that formation of the organometallic complex, Cu(CH3SO2)(CH3)(-), is energetically most favorable, in agreement with contrasting fragmentation pathways of copper and lanthanide complexes.
First author: Lashgari, A, Two fluoro compounds of main group elements: Synthesis,g characterization, theoretical and spectroscopic study, JOURNAL OF STRUCTURAL CHEMISTRY, 56, 1505, (2015)
Abstract: Two new compounds of fluorine: (C2H5)(4)N[I2F] and (C2H5)(4)N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)(4)NF, I-2 and Br-2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.
First author: Erbay, TG, How substitution tunes the electronic and transport properties ofg oligothiophenes, oligoselenophenes and oligotellurophenes, SYNTHETIC METALS, 210, 236, (2015)
Abstract: The geometrical, electronic and charge-transport properties of a series of unsubstituted and dicyanovinyl (DCV)-substituted oligothiophenes (nT), oligoselenophenes (nS) and oligotellurophenes (nTe) where n = 3-5 are investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT calculations. The intramolecular reorganization energy is found to decrease upon dicyanovinyl substitution, with a larger decrease for holes than electrons. The ground state HOMO and LUMO energies along with the Time-Dependent DFT calculations show smaller HOMO-LUMO gaps for the DCV-substituted oligomers. Calculations of the intermolecular charge transfer integrals in the crystals have been performed to understand the role of substitution on the charge-transport rate. DCV-substitution changes the packing motifs in the crystal and results in larger transfer integrals for holes along the pi-stacldng direction, calculated as -63 and -88 meV for DCV4T and DCV4S respectively. These results suggest that DCV-substituted oligomers studied here are more promising charge transporting materials than their unsubstituted analogues.
First author: Alonso, M, Metalated Hexaphyrins: From Understanding to Rational Design, CHEMISTRY-A EUROPEAN JOURNAL, 21, 17631, (2015)
Abstract: The heretofore unpredictable behavior of [26] and [28] hexaphyrins upon metalation has been elucidated through quantum chemical calculations. It is demonstrated that the molecular topology of Group 10 and Group 11 metal complexes of hexaphyrins depends on sensitive interplay between the intrinsic ligand strain and the metal-ligand interaction strength. As such, the aromaticity of the ligand and effective charge of the metal are revealed as key factors determining the binding mode and the preference for Mobius or Huckel structures. These findings offer a new perspective to rationalize experimental observations for metalated hexaphyrins. More importantly, the proposed guidelines could be useful for designing novel complexes of hexaphyrins, such as a hitherto unknown Mobius [26] hexaphyrin complex.
First author: Nizovtsev, AS, Li4E8 (E = P, As, Sb, Bi) Clusters: The Quest for Realgar-Type [E-8](4-)g Zintl Anions, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 21, 5801, (2015)
Abstract: A systematic computational study focused on searching for the global minima and low-lying isomers of the Li4E8 (E = P, As, Sb, Bi) series of clusters is reported. The global-minimum structures of Li4P8, Li4As8, and Li4Sb8 as well as one of the lowest-lying Li4Bi8 isomers were found to contain a realgar-type [E-8](4-) unit, which is a rare Zintl anion. Increased stability of this skeleton allows its presence to be expected in more complex chemical compounds containing group 15 elements with appropriate stoichiometry.
First author: Wadepohl, H, Structures and bonding of homoleptic bis(2,3-dihydro-1,3-diborole)g complexes of nickel and platinum, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 798, 146, (2015)
Abstract: Homoleptic metal complexes of the boron heterocycle 2,3-dihydro-1,3-diborole f((RC)-C-1)(2)((RB)-B-2)(2)R-3(H)C} 1 are described. X-Ray crystal structure determinations of two nickel and platinum derivatives are presented. In the nickel complex [Ni(1d)(2)] 6d (R-1 = R-2 = R-3 = Et) the essentially coplanar heterocycles attain a pentahapto coordination mode with a gauche orientation with respect to one another. An 18 VE count is attained. In contrast, in the 14 VE platinum complex [Pt(1a)(2)] 4a (R-1 = R-2 = Et, R-3 = Me) the ligands are strongly folded and adopt a tetrahapto coordination. The molecule is centrosymmetric in the crystalline state. DFT MO calculations are presented to establish the relative stabilities of these coordination modes for nickel and platinum, respectively.
First author: Pandey, KK, Structure and bonding analysis of germanones [(Eind)(2)Ge=O], [((Tbt))g (Tip)Ge=O] and [R2Ge=O] (R = Me, Ph): Significance of the dispersiong interactions, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1073, 20, (2015)
Abstract: Dispersion corrected quantum-chemical calculations of the germanones [(Eind)(2)Ge=O] (I), [((Tbt))(Tip) Ge=O] (II) and [R2Ge=O] (III, R = Ph; IV, R = Me) were performed to evaluate the effect of noncovalent interactions on the dramatic stability of isolated germanone [(Eind)(2)Ge=O]. The investigations have been carried at DFT, DFT-D3(BJ) and DFT-DDSC level with BP86, PW91, PBE density functionals. The dispersion-corrected geometry of the compound [(Eind)(2)Ge=O] (Ge=O=1.668 angstrom) is in good agreement with the experimental geometry (Ge=O=1.6468(5) angstrom). The polarizations of the G-C sigma-bonds toward the carbon atoms and Ge=O sigma- and pi-bonds toward oxygen atom decreases on going from I to IV. Due to the largest polarizations of these bonds in germanone (I), the Ge-C and Ge=O bond distances are longest in (I). The lowering in charge on oxygen atom in [(Eind)(2)Ge=O] (I) retard its reactivity. The total contribution of Ge atom toward two Ge-C bonds are 50.60% in I < 57.18% in II < 59.70% in III < 63.02% in IV. The Ge-C bonds (longer Ge-C bond distances, smaller Mayer Ge-C bond orders, smaller values of BDE and interaction energy) in most stable germanone [(Eind)(2)GeO] (I) are weaker than the Ge-C bonds in germanpnes (II-IV) and do not support the trends of relative stability of germanones (I-IV). The D3(BJ) dispersion energy is largest for germanone [(Eind)(2)GeO]. Thus, compared to small molecules, large molecules are stabilized by dispersion interactions. The dispersion interactions between R center dot center dot center dot R and between R center dot center dot center dot GeO support the trends of relative stability of germanones (I-IV).
First author: Bleda, EA, Studies on spin state preferences in Fe(II) complexes, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1073, 139, (2015)
Abstract: We report modeling studies of high spin and low spin forms of the test set of problematic cases of pseudo-octahedral Fe(II) complexes defined by Ye and Neese. These include the most thoroughly studied spin crossover compound Fe(SCN)(2)(Phen)(2) and a more recently discovered Fe(II)-2,13-dimethyl-6,9-dio xa-3,12,18-triaza-bicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentene. Reliable estimates of the often small high-spin to low-spin energy gap require balanced treatment of electronic structure in very different bonding environments. Density functionals differ in their bias toward low spin or high spin configurations. For the test set defined by Ye and Neese, we describe the estimates of their energy gaps between high-spin and low-spin forms for 75 functionals; geometries are obtained by optimization with B3LYP with zero-order relativistic approximation (ZORA) in a triple-zeta quality basis. Fairly reliable results for high-spin to low-spin energy gaps are obtained by functionals IMP, HCTH, OPBE, and B3LYP*, and with the omega B97XD functional expressed in the cc-pVTZ basis, about half the size of the def2-QZVPP used by Ye and Neese. The best functionals are still biased systematically toward the high spin by about 20 kJ/mol. We apply these methods in a new study of a pseudo C-3v four coordinate crossover species reported by Scepaniak et al. Their four coordinate spin crossover complex of Fe with aryl-substituted scorpionate and N = P(Ph)(3) ligands is modeled by a truncated structure lacking aromatic substituents. These substituents appear to stabilize the lower spin. Reproducing the 80 K crossover temperature requires an empirical correction of about 12 kJ/mot in favor of the singlet for this truncated model system.
First author: Donald, KJ, Structure, bonding, relativistic effects, and dispersion in the group 12g dihalide (MX2)(3) clusters, with lessons from the extended solids, STRUCTURAL CHEMISTRY, 26, 1179, (2015)
Abstract: The prediction of crystal structures for inorganic solids remains a challenge at the frontier of materials science. We examine the relationship between the group 12 dihalide monomers, small oligomers (in particular the trimers), and the extended solids. The clusters are investigated at density functional B3PW91 and MP2 computational levels and at the M06-2X, B97D3, and CCSD(T) levels for the first time for special cases where dispersion is important. Significant patterns in the bonding preferences in the dimers and extended solids of these systems are known to reflect the rigidity of the linear monomers. The trimers evolve typically as one-dimensional extensions of the dimers, but the HgX2 systems are different: They form loosely bound clusters with a few competitive geometries emerging that imply several potential directions for continued and more strongly bond higher-order clusters. The very weak intermolecular interactions in the Hg systems appear only when relativistic effects are turned on. Otherwise, they behave precisely like their Zn and Cd analogues. The HgF2 trimers, which have not been considered before, are examined in detail as well. These trimers-especially the fluorides-are somewhat more polar than the isolated monomers and dimers, and we find evidence for a gradual switch to the ionic bonding regime in the HgF2 clusters on the way to the fluorite extended solid structure. Differences between geometrical preferences obtained at the MP2 versus the B3PW91 levels for the (HgX2)(3) clusters demonstrate the importance of dispersion interactions in the bonding. Successes are reported for other density functional methods that directly address dispersion.
First author: Smolentsev, G, Time-resolved X-ray absorption spectroscopy for the study of molecularg systems relevant for artificial photosynthesis, COORDINATION CHEMISTRY REVIEWS, 304, 117, (2015)
Abstract: Transition metal coordination compounds have a rich photochemistry and are interesting candidates as both light harvesters (photosensitizers) and catalysts in photocatalytic systems. Knowledge of electronic and molecular structure of excited states of photosensitizers and intermediates of catalysts is a key topic for rational design of systems for artificial photosynthesis. We describe recent advances in the field of time-resolved X-ray absorption spectroscopy that provide information on local structure around metal centers, their orbital structure and oxidation state, and thereby insights into the mechanisms of their photochemical reactions. Photosensitizers with metal centers, multicomponent molecular catalytic systems, and supramolecular model sensitizer-catalysts with two metal centers are used as examples to demonstrate the possibilities of the technique. We overview different experimental methods that can be used to investigate intermediates with lifetimes in the range from hundreds of picoseconds to hundreds of microseconds. Theoretical methods to extract the structural and electronic information from X-ray absorption near edge structure spectroscopy (XANES) are also discussed.
First author: Baiardi, A, Vibrationally resolved NEXAFS at C and N K-edges of pyridine,g 2-fluoropyridine and 2,6-difluoropyridine: A combined experimental andg theoretical assessment, JOURNAL OF CHEMICAL PHYSICS, 143, 117, (2015)
Abstract: In the present work, the near edge X-ray absorption spectroscopy (NEXAFS) spectra at both C and N K-edges of pyridine, 2-fluoropyridine, and 2,6-difluoropyridine have been studied both experimentally and theoretically. From an electronic point of view, both transition potential density functional theory and time-dependent density functional theory approaches lead to reliable results provided that suitable basis sets and density functionals are employed. In this connection, the global hybrid B3LYP functional in conjunction with the EPR-III basis set appears particularly suitable after constant scaling of the band positions. For the N K-edge, vertical energies obtained at these levels and broadened by symmetric Gaussian distributions provide spectra in reasonable agreement with the experiment. Vibronic contributions further modulate the band-shapes leading to a better agreement with the experimental results, but are not strictly necessary for semi-quantitative investigations. On the other hand, vibronic contributions are responsible for strong intensity redistribution in the NEXAFS C K-edge spectra, and their inclusion is thus mandatory for a proper description of experiments. In this connection, the simple vertical gradient model is particularly appealing in view of its sufficient reliability and low computational cost. For more quantitative results, the more refined vertical Hessian approach can be employed, and its effectiveness has been improved thanks to a new least-squares fitting approach.
First author: Pandey, KK, Theoretical insights into M-SO bonds in transition metal-sulfur monoxide, POLYHEDRON, 101, 230, (2015)
Abstract: Geometry, electronic structure and bonding analysis of the sulfur monoxide complexes [{N(SPMe2)(2)}(2)M (SO)] (M = Fe, Ru, Os) have been investigated with the DFT, DFT-D3 and DFT-D3(BJ) methods using density functionals BP86, PW91, BLYP, PBE, revPBE, and TPSS. The BP86 and PBE optimized geometries of complex [{N(SPMe2)(2)}(2)Ru(SO)] are in good agreement with the reported experimental values. The Mayer and Gopinathan-Jug bond orders confirm the presence of M-SO and S-O multiple bond characters. Hirshfeld charge analysis shows transfer of electron density from metal fragments to antibonding pi* orbital of SO ligand. Significant noncovalent interactions between metal fragment and SO ligand are observed in the studied sulfur monoxide complexes. Noncovalent M—O and S—SO interactions have been justified by molecular orbital analysis. The M-SO bond dissociation energies vary in the order Fe < Ru < Os and depends on the choice of density functionals. The BP86/D3(BJ) dispersion corrections add 38% to the bond dissociation energy of Fe-SO bond, while only 22% and 17% to Ru-SO and Os-SO bonds, respectively. The pi-bonding contributions to the total M-SO bonds are relatively smaller (22.6-27.0%) than the sigma-bonding contribution.
First author: Bhattacharyya, K, Small Organic Molecules for Efficient Singlet Fission: Role of Silicong Substitution, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 25696, (2015)
Abstract: Singlet fission (SF) has emerged as an important mechanism for enhancing the efficiency of organic solar cells. In search for new molecules for SF, silicon substituted oligoacenes are shown to be excellent candidates. Here we show that monosilicon substitution in the central ring of anthracene is found to be the smallest closed shell molecule predicted to exhibit SF. The crystal structure of 10-cyano-9-silaanthracene (10-CN-9-SA) shows the molecules in slipped parallel stacked orientations with small intermolecular distances (d(center-center) = 4.13 angstrom). We have performed calculations using the Marcus electron transfer theory to calculate the SF rate in a chromophoric pair. Our calculation indicates that the lowest energy CT state mediates as a real intermediate in a SF pathway maximizing the SF rate. Short intermolecular contacts and low-lying charge transfer (CT) states lead to an anticipated triplet yield of similar to 200% in the SF process for these crystals. An indirect one-electron integral mechanism through a CT state predominates over the direct two-electron integral mechanism for this extremely efficient SF.
First author: Thomas, KE, Ligand Noninnocence in Coinage Metal Corroles: A Silver Knife-Edge, CHEMISTRY-A EUROPEAN JOURNAL, 21, 16839, (2015)
Abstract: A silver beta-octabromo-meso-triarylcorrole has been found to exhibit a strongly saddled geometry, providing the first instance of a strongly saddled corrole complex involving a metal other than copper. The Soret maxima of the Ag octabromocorroles also redshift markedly in response to increasingly electron-donating para substituents on the mesoaryl groups. In both these respects, the Ag octabromocorroles differ from simple Ag triarylcorrole derivatives, which exhibit only mild saddling and substituent-insensitive Soret maxima. These results have been rationalized in terms of an innocent M-III-corrole(3-) description for the simple Ag corroles and a noninnocent M-II-corrole(center dot 2-) description for the Ag octabromocorroles. In contrast, all copper corroles are thought to be noninnocent, while all gold corroles are innocent. Uniquely among metallocorroles, silver corroles thus seem poised on a knife-edge, so to speak, between innocent and noninnocent electronic structures and may tip either way, depending on the exact nature of the corrole ligand.
First author: Hewage, JW, Metal-Metal Bonding in Trinuclear, Mixed-Valence [Ti3X12](4-) (X = F,g Cl, Br, I) Face-Shared Complexes, INORGANIC CHEMISTRY, 54, 10632, (2015)
Abstract: Metal-metal bonding in structurally characterized In4Ti3Br12,, comprising linear, mixed-valence d(1)d(2)d(1) face-shared [Ti3Br12](4-) units with a Ti-Ti separation of 3.087 angstrom and strong antiferromagnetic coupling (Theta = -1216 K), has been investigated using density functional theory. The antiferromagnetic configuration, in which the single d electron on each terminal Ti-III (d(1)) metal center is aligned antiparallel to the two electrons occupying the central Ti-II (d(2)) metal site, is shown to best agree with the reported structural and magnetic data and is consistent with an S = 0 ground state in which two of the four metal-based electrons are involved in a twoelectron, three-center sigma bond between the Ti atoms (formal Ti-Ti bond order of similar to 0.5). However, the unpaired spin densities on the Ti sites indicate that while the metal-metal a interaction is strong, the electrons are not fully paired off and consequently dominate the ground state antiferromagnetic coupling. The same overall partially delocalized bonding regime is predicted for the other three halide [Ti3X12](4-) (X = F, Cl, I) systems with the metal-metal bonding becoming weaker as the halide group is descended. The possibility of bond-stretch isomerism was also examined where one isomer has a symmetric structure with identical Ti-Ti bonds while the other is unsymmetric with one short and one long Ti-Ti bond. Although calculations indicate that the latter form is more stable, the barrier to interconversion between equivalent unsymmetric forms, where the short Ti-Ti bond is on one side of the trinuclear unit or the other, is relatively small such that at room temperature only the averaged (symmetric) structure is likely to be observed.
First author: Mei, L, Silver Ion-Mediated Heterometallic Three-Fold Interpenetrating Uranylg Organic Framework, INORGANIC CHEMISTRY, 54, 10934, (2015)
Abstract: A unique case of a uranyl-silver heterometallic 3-fold interpenetrating network (U-Ag-2,6-DCPCA) from a multifunctionalized organic ligand, 2,6-dichloroisonicotinic acid, in the presence of uranyl and silver ions is reported. It is the first report of a heterometallic uranylorganic interpenetrating network or framework. Notably, a (4,4)-connected uranyl building unit in U-Ag-2,6-DCPCA, which is available through combined influences of structural halogenation and silver ion additive on uranyl coordination, plays a vital role in the formation of a 3-fold interpenetrating network. Halogen substitution effectively changes structural features and coordination behaviors of isonicotinate ligand and contributes to the control of uranyl coordination. Meanwhile, it exerts influence on the stabilization of 3-fold interpenetrating networks by halogen-halogen interactions. Theoretical calculation suggests that the silver ion should mainly serve as an inductive factor of uranyl species through strong Ag-N binding affinity, directly leading to the formation of a (4,4)-connected uranyl building unit and finally a heterometallic 3-fold interpenetrating network. Related experimental results, especially an interesting postsynthetic metalation, afford further evidence of this induction effect.
First author: Zhou, WH, Electronic Transport Properties of Asymmetric Metal String Complexg [Cu2Pt(npa)(4)X-2](X=Cl-, NCS-), ACTA CHIMICA SINICA, 73, 1214, (2015)
Abstract: The asymmetric heterometal string complexes [Cu2Pt(npa)(4)X-2] (X= Cl-(1), NCS-(2), npa=2-naphthyridyl-phenylamine) are suitable candidates for promising inorganic molecule rectifiers. The electronic structures and transmission properties of them were investigated by theoretical calculation using Density Function Theory BP86 and Non Equilibrium Green's Functions method. The results revealed that: (1) Since the interaction between axial ligand NCS- and Cu atom is stronger than that of Cl-Cu, the Cu-Cu bond of complex 1 is stronger than that in 2, while its Cu-Pt bond is weaker than that in 2. Therefore, complex 1 has smaller energy gap Delta E between pi*(pt dxz/yz) and pi*(Cu-Cu) orbital compared with that of 2. (2) The transmission channels of 1 and 2 both are beta spin pi* orbitals, which are mainly combination of pi*(Cu-Cu), and pi*(pt dxz/yz) orbital. The smaller Delta E, the larger delocalization of pi* channel, and hence the stronger transmission capacity. When the positive bias is less than 0.15 V and under negative bias, current of 1 is greater than that of 2 for the smaller Delta E of 1. However when the positive bias is larger than 0.15 V, current of 2 is significantly higher than that of 1 for the stronger delocalization of it channel in 2. (3) The complex 2 has better rectifying effect. With a larger Delta E, the transmission of Pt -> Cu direction is easier and the rectifying effect is stronger. Current of 2 under the positive bias is significantly greater than that in negative bias. When the bias is larger than 0.15 V, the rectified ratio of 2 is 10 similar to 40 times larger than 1. (4) With the Delta E-beta smaller than Delta E-alpha, the transmission capacity of alpha spin channel is less than beta, and the effect of the spin filter will be stronger for the larger difference between Delta E-beta and Delta E-alpha. Both 1 and 2 have significant spin filter effect (up to 80%similar to 99%).
First author: Farberovich, OV, Quantum model of a solid-state spin qubit: Ni cluster on a silicong surface by the generalized spin Hamiltonian and X-ray absorptiong spectroscopy investigations, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 394, 422, (2015)
Abstract: We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density-functional scheme for the calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange coupling parameters linking the nickel ions with a silicon substrate. In this model the interaction of a spin qubit with substrate is considered in GSH at the calculation of exchange integrals Li of the nanosystem in the one-electron approach taking into account chemical bonds of all Si-atoms of a substrate (environment) with atoms of the Ni-7-cluster. The energy pattern was found from the effective GSH Hamiltonian acting in the restricted spin space of the Ni ions by the application of the irreducible tensor operators (ITO) technique. In this paper we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on the silicon surface. The solution of the problem of the entanglement between spin states in the N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement (DOE). In this study we have developed and used the advanced high precision numerical techniques to accurately assess the details of the decoherence process governing the dynamics of the N-spin qubits interacting with a silicon surface. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time (0.327 mu s). The comparison of the energy pattern with the anisotropic exchange models conventionally used for the analysis of this system and, with the results of the experimental XANES spectra, shows that our complex investigations provide a good description of the pattern of the spin levels and the spin structures of the nanomagnetic Ni-7 qubit. The results are discussed in the view of the general problem of the solid-state spin qubits and the spin structure of the Ni cluster.
First author: Jones, DB, Electron- and photon-impact ionization of furfural, JOURNAL OF CHEMICAL PHYSICS, 143, 422, (2015)
Abstract: The He(I) photoelectron spectrum of furfural has been investigated, with its vibrational structure assigned for the first time. The ground and excited ionized states are assigned through ab initio calculations performed at the outer-valence Green's function level. Triple differential cross sections (TDCSs) for electron-impact ionization of the unresolved combination of the 4a " + 21a' highest and next-highest occupied molecular orbitals have also been obtained. Experimental TDCSs are recorded in a combination of asymmetric coplanar and doubly symmetric coplanar kinematics. The experimental TDCSs are compared to theoretical calculations, obtained within a molecular 3-body distorted wave framework that employed either an orientation average or proper TDCS average. The proper average calculations suggest that they may resolve some of the discrepancies regarding the angular distributions of the TDCS, when compared to calculations employing the orbital average.
First author: Moqadam, M, A test on reactive force fields for the study of silica dimerizationg reactions, JOURNAL OF CHEMICAL PHYSICS, 143, 422, (2015)
Abstract: We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) and reactive force fields based on two parameterizations of ReaxFF. For each method (both ReaxFF force fields and DFT), we performed constrained geometry optimizations, which were subsequently evaluated in single point energy calculations using the other two methods. Standard fitting procedures typically compare the force field energies and geometries with those from quantum mechanical data after a geometry optimization. The initial configurations for the force field optimization are usually the minimum energy structures of the ab initio database. Hence, the ab initio method dictates which structures are being examined and force field parameters are being adjusted in order to minimize the differences with the ab initio data. As a result, this approach will not exclude the possibility that the force field predicts stable geometries or low transition states which are realistically very high in energy and, therefore, never considered by the ab initio method. Our analysis reveals the existence of such unphysical geometries even at unreactive conditions where the distance between the reactants is large. To test the effect of these discrepancies, we launched molecular dynamics simulations using DFT and ReaxFF and observed spurious reactions for both ReaxFF force fields. Our results suggest that the standard procedures for parameter fitting need to be improved by a mutual comparative method.
First author: Sahu, P, The entropic forces and dynamic integrity of single file water ing hydrophobic nanotube confinements, JOURNAL OF CHEMICAL PHYSICS, 143, 422, (2015)
Abstract: Water in nanotube exhibits remarkably different properties from the bulk phase, which can be exploited in various nanoconfinement based technologies. The properties of water within nanotube can be further tuned by varying the nanotube electrostatics and functionalization of nanotube ends. Here, therefore, we investigate the effect of quantum partial charges and carbon nanotube (CNT) termination in terms of associated entropic forces. An attempt has been made to correlate the entropic forces with various dynamical and structural properties. The simulated structural features are consistent with general theoretical aspects, in which the interfacial water molecules at H terminated CNT are found to be distributed in a different way as compared to other CNTs. The rotational entropy components for different cases of CNTs are well corroborated by the decay time of hydrogen bond (HB) correlation functions. A part of this event has been explained in terms of orientation of water molecules in the chain, i.e., the change in direction of dipole moment of water molecules in the chain and it has been revealed that the HBs of CNT confined water molecules show long preserving correlation if their rotations inside CNT are restricted. Furthermore, the translational entropy components are rationally integrated with the differing degree of translational constraints, added by the CNTs. To the best of our information, perhaps this is the first study where the thermodynamic effects introduced by H-termination and induced dipole of CNT have been investigated. Additionally, we present a bridge relation between "translational diffusivity and configurational entropy" for water transport from bulk phase to inside CNTs.
First author: Muck, FM, Reactivity of the Donor-Stabilized Silylenes [iPrNC(Ph)NiPr](2)Si andg [iPrNC(NiPr2)NiPr](2)Si: Activation of CO2 and CS2, CHEMISTRY-A EUROPEAN JOURNAL, 21, 16665, (2015)
Abstract: Activation of CO2 by the bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 leads to the structurally analogous six-coordinate silicon(IV) complexes 4 (previous work) and 8, respectively, the first silicon compounds with a chelating carbonato ligand. Likewise, CS2 activation by silylene 1 affords the analogous six-coordinate silicon(IV) complex 10, the first silicon compound with a chelating trithiocarbonato ligand. CS2 activation by silylene 2, however, yields the five-coordinate silicon(IV) complex 13 with a carbon-bound CS22- ligand, which also represents an unprecedented coordination mode in silicon coordination chemistry. Treatment of the dinuclear silicon(IV) complexes 5 and 6 with CO2 also affords the six-coordinate carbonatosilicon(IV) complexes 4 and 8, respectively.
First author: Safin, DA, Influence of the Homopolar Dihydrogen Bonding CHHC on Coordinationg Geometry: Experimental and Theoretical Studies, CHEMISTRY-A EUROPEAN JOURNAL, 21, 16679, (2015)
Abstract: The reaction of the N-thiophosphorylated thiourea (HOCH2)(Me)(2)CNHC(S)NHP(S)(OiPr)(2) (HL), deprotonated by the thiophosphorylamide group, with NiCl2 leads to green needles of the pseudotetrahedral complex [Ni(L-1,5-S,S)(2)]0.5(n-C6H14) or pale green blocks of the trans square-planar complex trans-[Ni(L-1,5-S,S)(2)]. The former complex is stabilized by homopolar dihydrogen CHHC interactions formed by n-hexane solvent molecules with the [Ni(L-1,5-S,S)(2)] unit. Furthermore, the dispersion-dominated CH HC interactions are, together with other noncovalent interactions (CHN, CHNi, CHS), responsible for pseudotetrahedral coordination around the Ni-II center in [Ni(L-1,5-S,S)(2)]0.5(n-C6H14).
First author: Su, DM, Highly Diverse Bonding between Two U3+ Ions When Ligated by a Flexibleg Polypyrrolic Macrocycle, ORGANOMETALLICS, 34, 5225, (2015)
Abstract: A Schiff-base polypyrrolic ligand (H4L) can accommodate two U3+ ions and form a Pacman-like complex [U-2(L)](2+) according to relativistic density functional theory. Sixteen species, featuring four structural models in four electronic states, are energetically stable. Ligand flexibility, lack of axial restriction, and suitable U-N interactions allow the two U3+ ions to stretch freely over a wide range, in contrast to U-2@C-n (n = 60, 74, 80) studied previously. Diverse U3+-U3+ interactions are found. The quintet state of the Out-In model, which is calculated to be the global ground state both including and excluding the spin-orbit coupling energy, likely shows a weak single U-2 bond. In both vertical and tilt In-In species, a triple bond is found. It is composed of two two-electron-two-center bonds and two one-electron-two-center bonds; moreover, the tilt conformer is almost isoenergetic with Out-In. The Out-Out species shows no U center dot center dot center dot U bonding. Comparison with explicitly THF-solvated diuranium complexes is also addressed.
First author: Do, TG, Intramolecularly Group 15 Stabilized Aryltellurenyl Halides andg Triflates, ORGANOMETALLICS, 34, 5341, (2015)
Abstract: The preparation of a series of functionalized pen-substituted acenaphthyl compounds 6-Ph2E-Ace-5-Br (1, E = As; 2, E = Sb), 6-Ph2As-Ace-5-TeMes (3), 5-I-Ace6-TeMes (4), 6-Ph2Sb-Ace-5-TeMes (5), (6-Ph2P-Ace-5)(2)Te (6), [6-R2E-Ace-5-Te]X (7, E = P, R = Ph, X = Cl; 8, E = P, R = i-Pr, X = Cl; 9, E = P, R = i-Pr, X = Br; 10, E = P, R = i-Pr, X = I; 11, E = P, R = i-Pr, X = 1/2 (TeI6); 12, E = P, R = i-Pr, X = 13; 13, E = P, R = Ph, X = O3SCF3; 14, E = As, R = Ph, X = O3SCF3; 15, E = Sb, R = Ph, X = 03SCF3), and [6-PhSbAce-5-TeMes]O3SCF3 (16) is reported (Ace = acenaphthyl). The synthesis of 7-15 was achieved either by a salt metathesis reaction of 5-i-Pr2P-Ace-6-Li with TeCl2 center dot TMTU (8), TeBr2 center dot TMTU (9), and Tell. (10 + 11) or by the aryl cleavage reaction of 6-R2E-Ace-5-TeMes (E = P, As, Sb; R = Ph, i-Pr) with HgCl2 (7), I-2 (12), and HO3SCF3 (13-15). The reaction of 5 with triflic acid gave also rise to the formation of [6-PhSb-Ace-5-TeMes] O3SCF3 (16). All compounds have been characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. Complementary DFT studies including relaxed potential energy scans (PES) and subsequent topological analysis of the resulting electron and pair densities according to the AIM and ELI-D partitioning schemes were performed for the aryltellurenyl chlorides [6-Ph2P-Ace-S-Te]Cl, [8-Me2N-Nap-1-Te]Cl, and [8-Me2P-Nap-1-Te]Cl in the gas phase and in MeCN solution, whereby the Te-Cl distances were systematically varied. The same analyses were carried out for the fully optimized [6-R2E-Ace-5-Te](+) cations (E = P, As, Sb) and compared to those of the previously studied intermolecularly stabilized [R(3)ETeMes](+) cations (E = P, As, Sb).
First author: Pan, S, A Coupled-Cluster Study on the Noble Gas binding Ability of Metalg Cyanides Versus Metal Halides (Metal = Cu, Ag, Au), JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 2168, (2015)
Abstract: A coupled-cluster study is carried out to investigate the efficacy of metal(I) cyanide (MCN; M = Cu, Ag, Au) compounds to bind with noble gas (Ng) atoms. The M-Ng bond dissociation energy, enthalpy change, and Gibbs free energy change for the dissociation processes producing Ng and MCN are computed to assess the stability of NgMCN compounds. The Ng binding ability of MCN is then compared with the experimentally detected NgMX (X = F, Cl, Br) compounds. While CuCN and AgCN have larger Ng binding ability than those of MCl and MBr (M = Cu, Ag), AuCN shows larger efficacy toward bond formation with Ng than that of AuBr. Natural bond orbital analysis, energy decomposition analysis in conjunction with the natural orbital for chemical valence theory, and the topological analysis of the electron density are performed to understand the nature of interaction occurring in between Ng and MCN. The Ng-M bonds in NgMCN are found comprise an almost equal contribution from covalent and electrostatic types of interactions. The different electron density descriptors also reveal the partial covalent character in the concerned bonds.
First author: Kiawi, DM, Water Adsorption on Free Cobalt Cluster Cations, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 10828, (2015)
Abstract: Cationic cobalt clusters complexed with water Co-n(+)-H2O (n = 6-20) are produced through laser ablation and investigated via infrared multiple photon dissociation (IR-MPD) spectroscopy in the 200-1700 cm(-1) spectral range. All spectra exhibit a resonance close to the 1595 cm(-1) frequency of the free water bending vibration, indicating that the water molecule remains intact upon adsorption. For n = 6, the frequency of this band is blue-shifted, but it gradually converges to the free water value with increasing cluster size. In the lower-frequency range (200-650 cm(-1)) the spectra contain several bands which show a very regular frequency evolution, suggesting that the exact cluster geometry has little effect on the water surface interaction. Density functional theory (DFT) calculations are carried out at the OPBE/TZP level for three representative sizes (n = 6, 9, 13) and indicate that the vibrations responsible for the resonances correspond to bending and torsional modes between the cluster and water moieties. The potential energy surfaces describing these interactions are very shallow, making the calculated harmonic frequencies and IR intensities very sensitive to small geometrical perturbations. We conclude that harmonic frequency calculations on (local) minima structures provide insufficient information for these types of duster complexes and need to be complemented with calculations that provide a more extensive sampling of the potential energy surface.
First author: Zhang, Z, Controlling the Reactivity of the Boronyl Group in Platinum Complexesg toward Cyclodimerization: A Theoretical Survey, INORGANIC CHEMISTRY, 54, 10281, (2015)
Abstract: A theoretical study of the cyclodimerization of (Cy3P)(2)Pt(BO)Br (1Br) and [(Cy3P)(2)Pt(BO)](+) (1) (Cy = cyclohexyl) suggests that the reactivity of the BO ligand is primarily controlled by MgBO sigma donation. Therefore, increasing the electron density at the metal center through strong sigma-donor and weak pi-acceptor ancillary ligands and a low formal metal oxidation state are suggested to reduce the polarity of the boronyl ligand and thus lower its reactivity toward cyclodimerization. The stable 1Br has lower PtgBO sigma donation and thus a less electrophilic boron atom, leading to a less polarized BO ligand. However, 1 is unstable in dichloromethane, since the dicationic dimer and transition state are highly stabilized by strong electrostatic interactions.
First author: Gonzalez-Vazquez, JP, Interplay of Zero-Field Splitting and Excited State Geometry Relaxationg in fac-Ir(ppy)(3), INORGANIC CHEMISTRY, 54, 10457, (2015)
Abstract: The lowest energy triplet state, T-1, of organometallic complexes based on iridium(III) is of fundamental interest, as the behavior of molecules in this state determines the suitability of the complex for use in many applications, e.g., organic light-emitting diodes. Previous characterization of T-1 in fac-Ir(ppy)(3) suggests that the trigonal symmetry of the complex is weakly broken in the excited state. Here we report relativistic time dependent density functional calculations of the zero-field splitting (ZFS) of fac-Ir(ppy)(3) in the ground state (S-0) and lowest energy triplet (T-1) geometries and at intermediate geometries. We show that the energy scale of the geometry relaxation in the T-1 state is large compared to the ZFS. Thus, the natural analysis of the ZFS and the radiative decay rates, based on the assumption that the structural distortion is a small perturbation, fails dramatically. In contrast, our calculations of these quantities are in good agreement with experiment.
First author: Yeh, SW, Chelate-Thiolate-Coordinate Ligands Modulating the Configuration andg Electrochemical Property of Dinitrosyliron Complexes (DNICs), CHEMISTRY-A EUROPEAN JOURNAL, 21, 16035, (2015)
Abstract: As opposed to the reversible redox reaction ({Fe(NO)(2)}(10) reduced-form DNIC [(NO)(2)Fe(S(CH2)(3)S)](2-) (1){Fe(NO)(2)}(9) oxidized-form [(NO)(2)Fe(S(CH2)(3)S)](-)), the chemical oxidation of the {Fe(NO)(2)}(10) DNIC [(NO)(2)Fe(S(CH2)(2)S)](2-) (2) generates the dinuclear {Fe(NO)(2)}(9)-{Fe(NO)(2)}(9) complex [(NO)(2)Fe(-SC2H4S)(2)Fe(NO)(2)](2-) (3) bridged by two terminal [SC2H4S](2-) ligands. On the basis of the Fe K-edge pre-edge energy and S K-edge XAS, the oxidation of complex 1 yielding [(NO)(2)Fe(S(CH2)(3)S)](-) is predominantly a metal-based oxidation. The smaller S1-Fe1-S2 bond angle of 94.1(1)degrees observed in complex 1 (S1-Fe1-S2 88.6(1)degrees in complex 2), compared to the bigger bond angle of 100.9(1)degrees in the {Fe(NO)(2)}(9) DNIC [(NO)(2)Fe(S(CH2)(3)S)](-), may be ascribed to the electron-rich {Fe(NO)(2)}(10) DNIC preferring a restricted bite angle to alleviate the electronic donation of the chelating thiolate to the electron-rich {Fe(NO)(2)}(10) core. The extended transition state and natural orbitals for chemical valence (ETS-NOCV) analysis on the edt-/pdt-chelated {Fe(NO)(2)}(9) and {Fe(NO)(2)}(10) DNICs demonstrates how two key bonding interactions, that is, a FeS covalent sigma bond and thiolate to the Fe dz2 charge donation, between the chelating thiolate ligand and the {Fe(NO)(2)}(9/10) core could be modulated by the backbone lengths of the chelating thiolate ligands to tune the electrochemical redox potential (E-1/2=-1.64V for complex 1 and E-1/2=-1.33V for complex 2) and to dictate structural rearrangement/chemical transformations (S-Fe-S bite angle and monomeric vs. dimeric DNICs).
First author: Kumbhar, S, Cooperativity in bimetallic glutathione complexes, JOURNAL OF MOLECULAR GRAPHICS & MODELLING, 62, 1, (2015)
Abstract: Glutathione interacting with Au+, Ag+, and [HgMe](+) metal ions is investigated using density functional theory. An extensive conformational search shows that the sulfhydryl group of cysteine is the predominant binding motif for Au+, Ag+, and [HgMe](+). The order of binding affinities and binding free energies for the metal:ligand complexes are calculated at the B3LYP-D3(BJ)/def2-TZVP level of theory. Analysis of the gas-phase optimized structures has shown that the increase in the number of metal ions (1:1 -> 2:1) during the complex formation with a single glutathione leads to a strong cooperative behavior. Conversely, anti-cooperativity is demonstrated in implicit solvation corrections as well as in explicit solvent corrections to the energies in the explicitly solvated-phase structures optimized using a density-based adaptive QM/MM methodology.
First author: Kamps, JJAG, Chemical basis for the recognition of trimethyllysine by epigeneticg reader proteins, NATURE COMMUNICATIONS, 6, 1, (2015)
Abstract: A large number of structurally diverse epigenetic reader proteins specifically recognize methylated lysine residues on histone proteins. Here we describe comparative thermodynamic, structural and computational studies on recognition of the positively charged natural trimethyllysine and its neutral analogues by reader proteins. This work provides experimental and theoretical evidence that reader proteins predominantly recognize trimethyllysine via a combination of favourable cation-pi interactions and the release of the high-energy water molecules that occupy the aromatic cage of reader proteins on the association with the trimethyllysine side chain. These results have implications in rational drug design by specifically targeting the aromatic cage of readers of trimethyllysine.
First author: Poggio, S, Properties of transition metal doped cadmium sulfide hexamers andg dodecamers, CHEMICAL PHYSICS LETTERS, 640, 106, (2015)
Abstract: The electronic and geometrical properties of endohedrally and substitutionally doped Cd6S6 and Cd12S12 clusters were analyzed by means of Density Functional Theory. The results are compared to those of ZnS clusters of the same size. There is a clear correlation between CdS and ZnS when doped with the same element due to the chemical interaction between the dopant and its host. This is particularly evident from endohedrally doped Cd6S6. The change in properties across the 3d series in doped CdS clusters is not as great as in ZnS clusters.
First author: van Dijkman, TF, Bright Cyan Phosphorescence of a (Phosphane)copper(I) Complex of theg Trihydridopyrazolylborate Ligand H3B(3,5-Ph(2)Pz)(-), EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 640, 5387, (2015)
Abstract: The ligand trihydrido(3,5-diphenylpyrazol-1-yl) borate([ Mp(Ph2)](-)) has been synthesized from 3,5-diphenylpyrazole and sodium borohydride in N, N-dimethylformamide. By using this ligand, three phosphane-stabilized copper(I) complexes [Cu(Mp(Ph2))(L-2)] [L-2 = (PPh3)(2), 1,2-bis(diphenylphosphanyl) ethane(dppe), or 1,2-bis(diphenylphosphanyl) benzene (dppbz)] were synthesized. The complexes were characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography. The crystal structures of these complexes show that the copper ions are in trigonal-pyramidal geometries with the apical position formed by agostic Cu-H interactions between the Cu-I center and one of the hydride atoms of the borate ligand. Complexes [Cu-(Mp(Ph2))(PPh3)(2)] and [Cu(Mp(Ph2))(dppbz)] are mononuclear, whereas complex [Cu-2(Mp(Ph2))(2)(mu-dppe)(2)] is dinuclear with bridging dppe ligands. In the solid state, fluorescent emissions are observed in [Cu(Mp(Ph2))(PPh3)(2)] and [Cu-2(Mp(Ph2))(2)(mu-dppe)(2)] but not in [Cu(Mp(Ph2))(dppbz)], which exhibits bright cyan phosphorescence at room temperature that shifts to green when the sample is cooled to 77 K. The phosphorescence of [Cu(Mp(Ph2))(dppbz)] is attributed to mixed interligand and metal-to-ligand charge transfer (3)(MLCT + pi-pi*) excited states.
First author: Tyminska, N, DFT-D Investigation of Active and Dormant Methylaluminoxane (MAO)g Species Grafted onto a Magnesium Dichloride Cluster: A Model Study ofg Supported MAO, ACS CATALYSIS, 5, 6989, (2015)
Abstract: Density functional theory calculations were carried out to study the interaction of various models for methylaluminoxane and the active and dormant species in polymerization with the (110) MgCl2 surface. MAO species may bind to the surface via Al-Cl, Mg-O, and Al-mu-CH3-Mg bonds. Our results suggest that the activity of supported MAO may be higher than of homogeneous MAO because the support stabilizes (AlOMe)(n)center dot(AlMe3)(m), precursors to the active species in polymerization. Moreover, the support lowers the free energy of formation of species that are active in polymerization relative to those that are dormant. Finally, it may be that the support decreases the energy associated with the cation-anion separation in [Cp2ZrMe](+)[Me(AlOMe)(n)](-), a species that is likely dormant in homogeneous processes, hinting that the support has the possibility of increasing the number of potentially active sites.
First author: Heck, A, Multi-Scale Approach to Non-Adiabatic Charge Transport in High-Mobilityg Organic Semiconductors, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 5068, (2015)
Abstract: A linear scaling QM/MM model-for studying charge transport in high-mobility molecular semiconductors is Presented and applied to an anthracene single crystal and a hexabenzocoronene derivative in its liquid crystalline phase. The model includes both intra- and intermolecular electron-phonon couplings, long-range interactions with the environment, and corrections to the self-interaction error of density functional theory. By performing Ehrenfest simulations of the cationic system, hole mobilities are derived and compared to the experiment. A detailed picture of the charge carrier dynamics is given, and the performance of our method is discussed.
First author: Oliveira, AF, DFTB Parameters for the Periodic Table, Part 2: Energies and Energyg Gradients from Hydrogen to Calcium, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 5209, (2015)
Abstract: In the first part of this series, we presented a parametrization strategy to obtain high-quality electronic band structures on the basis of density-functional-based tight-binding (DFTB) calculations and published a parameter set called QUASINANO2013.1. Here, we extend our parametrization effort to include the remaining terms that are needed to compute the total energy and its gradient, commonly referred to as repulsive potential. Instead of parametrizing these terms as a two-body potential, we calculate them explicitly from the DFTB analogues of the Kohn-Sham total energy expression. This strategy requires only two further numerical parameters per element. Thus, the atomic configuration and four real numbers per element are sufficient to define the DFTB model at this level of parametrization. The QUASINANO2015 parameter set allows the calculation of energy, structure, and electronic structure of all systems composed of elements ranging from H to Ca. Extensive benchmarks show that the overall accuracy of QUASINANO2015 is comparable to that of well-established methods, including PM7 and hand-tuned DFTB parameter sets, while coverage of a much larger range of chemical systems is available.
First author: Goez, A, A Local Variant of the Conductor-Like Screening Model for Fragment-Basedg Electronic-Structure Methods, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 5277, (2015)
Abstract: Due to steadily rising computational power and sophisticated modeling approaches, increasingly larger molecular systems can be modeled with ab initio methods. An especially promising approach is subsystem methods, where the total system is broken down into smaller subunits that can be treated individually. If an implicit solvent environment such as the conductor-like screening model (COSMO) is included in the description, then additional environmental effects can be 500 incorporated at relatively low cost. For very large systems described with subsystem methods, however, the solution of the COSMO equations can actually become the bottleneck of the calculation. A prominent example in this area is biomolecular systems such as proteins, which can, for instance, be described with frozen density embedding (FDE), especially the related 3-FDE approach. In this article, we present an alternative COSMO variant, which exploits the subsystem nature of the underlying electronic description and has been implemented in a development version of the Amsterdam Density Functional program suite (A(DF)). We show that the computational cost for the solvent model can be reduced dramatically while retaining the accuracy of the regular description. We compare several schemes for density and surface charge updates and assess the effect of the single tuning parameter.
First author: Crawford, TD, Frozen-Density Embedding Potentials and Chiroptical Properties, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 5305, (2015)
Abstract: The efficacy of the frozen density embedding (FDE) approach to the simulation of solvent effects is examined for two key chiroptical properties-specific rotation and circular dichroism spectra. In particular, we have investigated the performance of a wave function-theory-indensity-functional-theory (WFT-in-DFT) FDE approach for computing such properties for the small, rigid chiral compound (P)-dimethylallene interacting with up to three water molecules. Although the solvent potential is obtained through DFT, the optical response is computed using coupled cluster linear response theory for mixed electric and magnetic field perturbations. We find that the FDE potential generally yields too small a shift from the isolated molecule as compared to that introduced by the explicit solvent. In one case, the FDE potential fails to reproduce a change in sign of the ORD in which the solute interacts with two solvent molecules. The source of these errors is due primarily to the lack of solvent response to the external field and is analyzed in terms of solvent-solute charge transfer excitations.
First author: Gonzalez-Torres, JC, The CO oxidation mechanism on small Pd clusters. A theoretical study, JOURNAL OF MOLECULAR MODELING, 21, 5305, (2015)
Abstract: CO is a pollutant that is removed by oxidation using Pd, Pt or Rh as catalysts in the exhaust pipes of vehicles. Here, a quantum chemistry study on the CO+O-2 reaction catalyzed by small Pd-n clusters (n <= 5) using the PBE/TZ2P/ZORA method is performed. The limiting step in this reaction at low temperature and coverage is the O-2 dissociation. Pdn clusters catalyze the O=O bond breaking, reducing the energy barrier from 119 kcal mol(-1) without catalyst to similar to 35 kcal mol(-1). The charge transfer from Pd to the O-2,O-ad antibonding orbital weakens, and finally breaks the O-O bond. The CO oxidation takes place by the Eley-Rideal (ER) mechanism or the Langmuir-Hinshelwood (LH) mechanism. The ER mechanism presents an energy barrier of 4.10-7.05 kcal mol(-1) and the formed CO2 is released after the reaction. The LH mechanism also shows barrier energies to produce CO2 (7-15 kcal mol(-1)) but it remains adsorbed on Pd clusters. An additional energy (7-25 kcal mol(-1)) is necessary to desorb CO2 and release the metal site. The triplet multiplicity is the ground states of studied Pd-n clusters, with the following order of stability: triplet>singlet>quintet state.
First author: Cazares-Larios, UE, Computational study of the structure, bonding and reactivity of selectedg helical metallocenes, INORGANICA CHIMICA ACTA, 438, 203, (2015)
Abstract: A series of helicoid metallocenes structures were studied in silico under the DFT framework. Their reactivity was explored by the dual Fukui function. An energy decomposition analysis was performed in order to gain insight into the interaction between the helix-like ligand and the metallic nuclei. Helical cobaltocene was highlighted as an interesting synthetic target through its peculiar response to ionization as well as its interaction and preparation energies.
First author: Jerzykiewicz, M, pH-dependent formation of Hg(II)-semiquinone complexes from naturalg phenols, CHEMOSPHERE, 138, 233, (2015)
Abstract: The ability of various natural phenols to form Hg(II)-semiquinone complexes was tested in the pH range of 2.8-12. EPR experiments performed at 9.6 and 34 GHz (the X- and Q-band, respectively) revealed that the complexes formed at low and high pH values exhibit a significant dissimilarity between their g-matrices (g-tensors), strongly suggesting that the complexes differ structurally. Our previous investigation on the low pH complex (Chemosphere 2015, 119, 479-484) had shown the Hg(II) ion to be tetracoordinated by two ligands, one of the ligands being monoprotonated with the unpaired electron mainly located on it. In order to reveal the molecular structure of the high pH form a DFT-based theoretical analysis was carried out in this work. For all the optimized model structures the g-matrices were computed and compared with their experimental counterparts. Good agreement was observed only if the geometry of the model Hg(II) complex was planar and the coordination sphere was composed of one fully deprotonated radical ligand and hydroxyl anions.
First author: Ahmadnezhad, M, Theoretical studies on the geometrical and electronic structures ofg supramolecule bis(2,2 '-bipyridine)-5-amino-1,10-phenanthrolineg ruthenium(II)/functionalized SWCNT dyads, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 86, 148, (2015)
Abstract: Functionalization of carbon nanotube (CNT) with multiple redox and photo active entities is one of the extensive processes due to its importance in building molecular or supramolecular electronic devices, solar energy storage and conversion systems. Thus, to have better understanding about structural aspects and correct electronic structure of these large systems, the quantum studies have gained increased popularity. In present study, we have investigated the structural and electronic properties of functionalized CNTs (fCNTs) with [Ru(bpy)(2)(5-NH2-1,10-Phen)](+2), (Ru-bpy-phen)(+2), supramolecule based on DFT calculations. Main attention has been applied to obtain stable configuration, binding energies and effect of functionalization on electronic behavior of the selected supramolcule. We also evaluate the effect of nanotube's diameter and chirality on electronic properties of considered supramolecule. Calculated binding energies show that interactipn between the (Ru-bpy-phen)(+2) and the host CNTs depends on the tube diameter while the chirality doesn't affect significantly on the binding nature of respected complex. We have also investigated the influence of non-local dispersion interactions (vdW) and temperature on the stability and electronic structure of the considered system. Results obtained from the ab initio MD simulations showed that increasing the temperature can affect the distance between C and N atoms in the linkage position. The charge analysis indicates the existence of remarkable charge transfer between (Ru-bpy-phen)(+2) as donor and fCNTs as acceptor moieties in the isolated molecule. In the presence of vdW forces and at higher temperature, the charge transfer was decreased but the direction of transferred charge remains unchanged.
First author: Patwardhan, S, Theoretical Investigation of Charge Transfer in Metal Organic Frameworksg for Electrochemical Device Applications, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 24238, (2015)
Abstract: For electrochemical device applications metal organic frameworks (MOFs) must exhibit suitable conduction properties. To this end, we have performed computational studies of intermolecular charge transfer in MOFs consisting of hexa-Zr-IV nodes and tetratopic carboxylate linkers. This includes an examination of the electronic structure of linkers that are derived from tetraphenyl benzene 1, tetraphenyl pyrene 2, and tetraphenyl porphyrin 3 molecules. These results are used to determine charge transfer propensities in MOFs, within the framework of Marcus theory, including an analysis of the key parameters (charge transfer integral t, reorganization energy lambda, and free energy change Delta G(0)) and evaluation of figures of merit for charge transfer based on the chemical structures of the linkers. This qualitative analysis indicates that delocalization of the HOMO/LUMO on terminal substituents increases t and decreases lambda, while weaker binding to counterions decreases Delta G(0), leading to better charge transfer propensity. Subsequently, we study hole transfer in the linker 2 containing MOFs, NU-901 and NU-1000, in detail and describe mechanisms (hopping and superexchange) that may be operative under different electrochemical conditions. Comparisons with experiment are provided where available. On the basis of the redox and catalytic activity of nodes and linkers, we propose three possible schemes for constructing electrochemical devices for catalysis. We believe that the results of this study will lay the foundation for future experimental work on this topic.
First author: Mahmoodinia, M, Chemical Bonding and Electronic Properties of the Co Adatom and Dimerg Interacting with Polyaromatic Hydrocarbons, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 24425, (2015)
Abstract: The density functional calculations presented here elucidate the nature of the interaction between the Co atom and dimer with a polyaromatic hydrocarbon (PAR). The results are analyzed in terms of structural, electronic, and magnetic properties. The bonding character of the Co atom and dimer adsorbed on the PAH exhibits a strong covalent bonding, arising from a hybridization between the d orbitals of Co and the p(z) orbitals of the carbon atoms, which cause an inplane distortion in the PAHs. A small charge transfer takes place from the Co atom and dimer to the PAR surface, which creates a positive charge on the metal atoms and thereby changes their catalytic activity. Upon adsorption, the magnetic moment of the Co adatom is reduced depending on the adsorption site. For the perpendicular Co dimer to the PAR plane, the projected magnetic moment of the Co atom further from the PAR is increased, which is due to antiferromagnetic coupling between the Co atoms in this configuration. Density of state analysis shows that the main contribution of magnetic moment reduction is due to promotion of electrons from the 4s states to the 3d states of the Co adatom upon adsorption.
First author: Luy, JN, Rhodium(I) and Iridium(I) Complexes of the Conformationally Rigidg IBioxMe(4) Ligand: Computational and Experimental Studies of Unusuallyg Tilted NHC Coordination Geometries, ORGANOMETALLICS, 34, 5099, (2015)
Abstract: Computational methods have been used to analyze distorted coordination geometries in a coherent range of known and new rhodium(I) and iridium(I) complexes containing bioxazoline-based NHC ligands (IBiox). Such distortions are readily placed in context of the literature through measurement of the Cnt(NHC)-C-NCN-M angle (Theta(NHC); Cnt = ring centroid). On the basis of restricted potential energy calculations using cis-[M(IBioxMe(4))(CO)(2)Cl] (M1; M = Rh, Ir), in-plane (yawing) tilting of the NHC was found to incur significantly steeper energetic penalties than orthogonal out-of-plane (pitching) movement, which is characterized by noticeably flat potential energy surfaces. Energy decomposition analysis (EDA) of the ground-state and pitched structures of M1 indicated only minor differences in bonding characteristics. In contrast, yawing of the NHC ligand is associated with a significant increase in Pauli repulsion (i.e., sterics) and reduction in M -> NHC pi back donation, but is counteracted by supplemental stabilizing bonding interactions only possible due to the closer proximity of the methyl substituents with the metal and ancillary ligands. Aided by this analysis, comparison with a range of carefully selected model systems and EDA, distorted coordination modes in trans-[M(IBioxMe(4))(2)(COE)Cl] (M2; M = Rh, Ir) and [M(IBioxMe(4))(3)](+) (M3; M = Rh, Ir) have been rationalized. Steric interactions were identified as the major contributing factor and are associated with a high degree of NHC pitching. In the case of Rh3, weak agostic interactions also contribute to the distortions, particularly with respect to NHC yawing, and are notable for increasing the bond dissociation energy of the distorted ligands. Supplementing the computational analysis, an analogue of the formally 14 VE Rh(I) species Rh3 bearing the cyclohexyl-functionalized IBiox6 ligand ([Rh(IBiox6)(3)](+), Rh3-Cy) was prepared and found to exhibit an exceptionally distorted NHC ligand (Theta(NHC) = 155.7(2)degrees) in the solid state.
First author: Yoneya, M, Origin of the High Carrier Mobilities of Nonperipheral Octahexylg Substituted Phthalocyanine, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 23852, (2015)
Abstract: The carrier transport properties of nonperipheral octahexyl substituted phthalocyanine H2Pc(C6H13)(8)(np) in its crystal and columnar (Col) liquid crystal (LC) phase were investigated using density functional theory (DFT) calculations in combination with molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. In the crystal phase, we found that the nonperipherally substituted chains of H2Pc(C6H13)(8)(np), that interpenetrate adjacent phthalocyanines (Pcs), significantly alter the Pc-core stacking such that higher hole mobilities are observed for this system than for the nonsubstituted H2Pc. This chain interpenetration was found to be inherited by the column stacking in the Col phase and hindered the Pc-core in-plane rotations between adjacent Pcs. This rotational hindrance further caused a nonuniform distribution of the adjacent dimer Pc-core in-plane orientation configurations. The relatively high carrier mobility in the Col phase in this system can be rationalized by the nonuniform distribution of the dimer configurations that give relatively high electronic coupling between the adjacent dimers. Our results show the remarkable effects of nonperipheral substitutions on the carrier transport properties in both the crystal and Col LC phases.
First author: Senn, F, Excited State Studies of Polyacenes Using the All-Order Constrictedg Variational Density Functional Theory with Orbital Relaxation, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 10575, (2015)
Abstract: For the polyacenes series from naphthalene to hexacene, we present the vertical singlet excitation energies 1 L-1(a) and L-1(b), as well as the first triplet excitation energies obtained by the all-order constricted variational density functional theory with orbital relaxation (R-CV(infinity)-DFT). R-CV(infinity)-DFT is a further development of variational density functional theory (CV(infinity)-DFT), which has already been successfully applied for the calculation of the vertical singlet excitation energies L-1(a) and L-1(b) for polyacenes,(15) and we show that one obtains consistent excitation energies using the local density approximation as a functional for singlet as well as for triplet excitations when going beyond the linear response theory. Furthermore, we apply self-consistent field density functional theory (Delta SCF-DFT) and compare the obtained excitation energies for the first triplet excitations T-1, where, due to the character of the transition, Delta SCF-DFT and R-CV(infinity)-DFT become numerically equivalent, and for the singlet excitations L-1(a) and 1 L-1(b), where the two methods differ.
First author: Sagan, F, From Saturated BN Compounds to Isoelectronic BN/CC Counterparts: Ang Insight from Computational Perspective, CHEMISTRY-A EUROPEAN JOURNAL, 21, 15299, (2015)
Abstract: In the present study, the inorganic analogues of alkanes as well as their isoelectronic BN/CC counterparts that bridge the gap between organic and inorganic chemistry are comparatively studied on the grounds of static DFT and Car-Parrinello molecular dynamics simulations. The BN/CC butanes CH3CH2BH2NH3, BH3CH2NH2CH3, and NH3CH2BH2CH3 were considered and compared with their isoelectronic counterparts NH3BH2NH2BH3 and CH3CH2CH2CH3. In addition, systematical replacement of the NH2BH2 fragment by the isoelectronic CH2CH2 moiety is studied in the molecules H3N(NH2BH2)(3-m)(CH2CH2)(m)BH3 (for m=0, 1, 2, or 3) and H3N(NH2BH2)(2-m)(CH2CH2)(m)BH3 (for m=0, 1, or 2). The DFT and Car-Parrinello simulations show that the isosteres of the BN/CC butanes CH3CH2BH2NH3, BH3CH2NH2CH3, and NH3CH2BH2CH3 and of larger oligomers of the type (BN)(k)(CC)(l) where kl are stable compounds. The BN/CC butane H3NCH2CH2BH3 spontaneously produces molecular hydrogen at room temperature. The reaction, prompted by very strong dihydrogen bonding NHHB, undergoes through the neutral, hypervalent, pentacoordinated boron dihydrogen complex RBH2(H-2) [R=(CH2CH2)(n)NH2]. The calculations suggest that such intermediate and the other BN/CC butanes CH3CH2BH2NH3, BH3CH2NH2CH3, and NH3CH2BH2CH3 as well as larger BN/CC oligomers are viable experimentally. A simple recipe for the synthesis of CH3CH2BH2NH3 is proposed. The strength of the dihydrogen bonding appeared to be crucial for the overall stability of the saturated BN/CC derivatives.
First author: Tang, QQ, Sc2O@C-2v(5)-C-80: Dimetallic Oxide Cluster Inside a C-80 Fullerene Cage, INORGANIC CHEMISTRY, 54, 9845, (2015)
Abstract: A new oxide cluster fullerene, Sc2O@C-2v(5)-C-80, has been isolated and characterized by mass spectrometry, UV-vis-NIR absorption spectroscopy, cyclic voltammetry, Sc-45 NMR, DFT calculations, and single crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to C-2v(5)-C-80 and suggests that the Sc2O cluster is ordered inside the cage. The crystallographic data further reveals that the Scl-O-Sc2 angle is much larger than that found in Sc2O@T-d(19151)-C-76 but almost comparable to that in Sc2O@C-s(6)-C-82, suggesting that the endohedral Sc2O unit is flexible and can display large variation in the Sc-O-Sc angle, which depends on the size and shape of the cage. Computational studies show that there is a formal transfer of four electrons from the Sc2O unit to the C-80 cage, i.e., (Sc2O)(4+)@(C-80)(4-), and the HOMO and LUMO are mainly localized on the C-80 framework. Moreover, thermal and entropic effects are seen to be relevant in the isomer selection. Comparative studies between the recently reported Sc2C2@C-2v(5)-C-80 and Sc2O@C-2v(5)-C-80 rev(e)al that, despite their close structural resemblance, subtle differences exist on the crystal structures, and the clusters exert notable impact on their spectroscopic properties as well as interactions between the clusters and corresponding cages.
First author: Chakraborty, D, Interaction of BN- and BP-doped graphene nanoflakes with someg representative neutral molecules and anions, MOLECULAR PHYSICS, 113, 2916, (2015)
Abstract: The interaction of BN- and BP-doped graphene nanoflakes with some representative neutral molecules and anions (H2O, HF, SH-, CH3O-, BO2-, F-) has been studied through density functional theory (DFT) calculations. The neutral molecules remain physisorbed whereas all the anions but one remains chemisorbed. Thermodynamically, most of the studied systems are found to be stable. Conceptual DFT-based reactivity descriptors were employed in order to provide rationale behind such observation. The nature of interactions in cases of the anions is predominantly of covalent type whereas the same for neutral molecules is of non-covalent type. The electrostatic and orbital interactions play important roles in stabilising the absorbed moieties. The kinetic stability of the absorbed moieties is confirmed through an atom-centred density matrix propagation simulation at 298 K temperature up to 500 fs. All the studied systems show excellent kinetic stability and remain absorbed up to 500 fs exhibiting rich vibrational and rotational dynamical evolutions.
First author: Aleksic, J, Origin of Fluorine/Sulfur Gauche Effect of beta-Fluorinated Thiol,g Sulfoxide, Sulfone, and Thionium Ion, JOURNAL OF ORGANIC CHEMISTRY, 80, 10197, (2015)
Abstract: The well-known gauche preference in FCCX systems, where X is an electronegative element from Period 2, is widely exploited in synthetic, medicinal, and material chemistry. It is rationalized on the basis of sigma(C-H)->sigma*(C-F) hyperconjugation and electrostatic interactions. The recent report (Thiehoff, C.; et al. Chem. Sci. 2015, 6, 3565) showed that the fluorine gauche effect can extend to Period 3 elements, such as sulfur. The aim of the present work is to disclose factors governing conformational behavior of FCCS containing systems. We examine conformational preferences in seven classes of compounds by ab initio and DFT calculations and rationalize the results by quantitatively decomposing the anti/gauche isomerization energy into contributions from electrostatic, orbital, dispersion, and Pauli interactions, and energy spent on structural changes. The results show that the fluorine/sulfur gauche effect is primarily electrostatic (63-75%), while all orbital interactions contribute 22-41% to stabilizing interactions. Stereoelectronic effects, involved in orbital interactions, also play a role in gauche conformer stabilization.
First author: Liu, J, Blockage of Water Flow in Carbon Nanotubes by Ions Due to Interactionsg between Cations and Aromatic Rings, PHYSICAL REVIEW LETTERS, 115, 10197, (2015)
Abstract: Combining classical molecular dynamics simulations and density functional theory calculations, we find that cations block water flow through narrow (6,6)-type carbon nanotubes (CNTs) because of interactions between cations and aromatic rings in CNTs. In wide CNTs, these interactions trap the cations in the interior of the CNT, inducing unexpected open or closed state switching of ion transfer under a strong electric field, which is consistent with experiments. These findings will help to develop new methods to facilitate water and ion transport across CNTs.
First author: Andjelkovic, L, Density functional theory study of the multimode Jahn-Teller problem ing the open-shell corannulenes and coronenes, CHEMICAL PHYSICS, 460, 64, (2015)
Abstract: Analysis of the multimode Jahn-Teller (JT) distortion in anions and cations of corannulene and coronene is presented, combining multideterminantal-DFT (MD-DFT) and Intrinsic Distortion Path (IDP) methods. The JT distortion is derived from the sum of contributions of all possible JT active normal modes. The C-C stretching modes play the most important role in the stabilization of the systems, in all investigated species, pushing the nuclei toward the minima on the potential energy surface. The further inspection of the IDP revealed that the relaxation of the geometry arrives in the final part of the path and is encountered by the softest vibrational modes. The same trend was observed in cyclopentadienyl radical, benzene anion, benzene cation and fullerene ions. This gives microscopic origin into the mechanism of the distortion and provides general behavior of the JT effect in these similar molecules. Moreover, MD-DFT and IDP, as fast and fully non-empirical approaches, can be considered as a reliable tool for better understanding of the JT effect.
First author: Fihey, A, SCC-DFTB Parameters for Simulating Hybrid Gold-Thiolates Compounds, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 2075, (2015)
Abstract: We present a parametrization of a self-consistent charge density functional-based tight-binding scheme (SCC-DFTB) to describe gold-organic hybrid systems by adding new Au-X (X = Au, H, C, S, N, O) parameters to a previous set designed for organic molecules. With the aim of describing goldthiolates systems within the DFTB framework, the resulting parameters are successively compared with density functional theory (DFT) data for the description of Au bulk, Aun gold clusters (n52, 4, 8, 20), and AunSCH3 (n = 3 and 25) molecular-sized models. The geometrical, energetic, and electronic parameters obtained at the SCC-DFTB level for the small Au3SCH3 gold-thiolate compound compare very well with DFT results, and prove that the different binding situations of the sulfur atom on gold are correctly described with the current parameters. For a larger gold-thiolate model, Au25SCH3, the electronic density of states and the potential energy surfaces resulting from the chemisorption of the molecule on the gold aggregate obtained with the new SCC-DFTB parameters are also in good agreement with DFT results.
First author: Xu, W, Stable structures of LnSi(6)(-) and LnSi(6) clusters (Ln = Pr, Eu, Gd,g Tb, Yb), C-2v or C-5v? Explanation of photoelectron spectra, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1070, 1, (2015)
Abstract: Theoretical investigation is performed on LnSig(6)(-)/LnSi(6) clusters to find their stable structures and explain experimental photoelectron (PE) spectra. The calculation is done by quasi-relativistic density functional (DF) theory at scalar level. The ground state geometry of LnSig(6)(-) is found to be either C-5v or C-2v, according to 4f configuration, while the neutral clusters all prefer C-2v symmetry. Covalent interaction between Ln(5d) and Si(3p) helps stabilize the molecules. The experimental PE spectra are simulated and explained. LnSig(6)(-)/LnSi(6) (Ln = Eu, Yb) clusters have 4f-character peaks in their spectra.
First author: Leblanc, C, Vanadium haloperoxidases: From the discovery 30 years ago to X-rayg crystallographic and V K-edge absorption spectroscopic studies, COORDINATION CHEMISTRY REVIEWS, 301, 134, (2015)
Abstract: In the environment, vanadium-dependent haloperoxidases (VHPO) are likely to play a key role in the production of biogenic organohalogens. These enzymes contain vanadate as a prosthetic group, and catalyze, in the presence of hydrogen peroxide, the oxidation of halide ions (Cl-, Br- or I-). They are classified according to the most electronegative halide that they can oxidize. Since the first discovery of a vanadium bromoperoxidase in the brown alga Ascophyllum nodosum 30 years ago, structural and mechanistic studies have been mainly conducted on two types of VHPO, chloro- and bromoperoxidases, and more recently on a vanadium-dependent iodoperoxidase. In this review, we highlight the main progress obtained on the structure-function relation of these proteins, based on biochemistry, crystallography and X-ray absorption spectroscopy (XAS). The comparison of 3D protein structures of the different VHPO helped identify the residues that govern the molecular mechanisms of catalysis and specificity of VHPO. Vanadium K-edge XAS gave further important insight to understand the fine changes around the vanadium cofactor during the catalytic cycle. The combination of different structural approaches, at different scales of resolution, shed new light on biological vanadium coordination in the active site, and its importance for the catalytic cycle and halide specificity of vanadium haloperoxidases.
First author: Pandey, KK, Quantum chemical insight into C-H center dot center dot center dot Fg bonding interactions between noncovalently bonded ion-pairs ing N-heterocyclic carbene complexes of gold(I) [(NHC*)(2)Au](+)[PF6](-) andg gold(III) [(NHC*)(2)AuCl2](+)[ PF6](-), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 795, 34, (2015)
Abstract: New insights into ion-pairs interactions in N-heterocyclic carbene complexes of gold(I) [(NHC*)(2)Au](+)[PF6](-) and gold(III) [(NHC*)(2)AuCl2](+)[PF6](-) (NHC* = 1-methyl-2-pyridin-2-yl-2H-imidazo [1,5-a] pyridine-4-ylium hexafluorophosphate) have been investigated at DFT and DFT-D3(BJ) level of theory with density functionals BP86 and PBE with particular emphasis on the (i) bonding energy analysis between anion [PF6](-) and cations [(NHC*)(2)Au](+), [(NHC*)(2)AuCl2](+) and (ii) effects of the non-covalent interactions between ion-pairs on the structures and the nature of AueC(NHC*) bond in ionic complexes [(NHC*)(2)Au](+)[PF6](-), [(NHC*)(2)AuCl2](+)[PF6](-) and as well as in cationic [(NHC*)(2)Au](+), [(NHC*)(2)AuCl2](+) complexes. The hydrogen-bonding interactions are stronger in Au(III) complex [(NHC*)(2)AuCl2](+) [PF6](-) (II) than in Au(I) complex [(NHC*)(2)Au](+)[PF6](-) (I). The carbene ligands donate about 0.20 electronic charge to the [PF6](-) anion. The contributions of the electrostatic interaction Delta E-elstat are significantly greater than the covalent bonding Delta E-orb interaction. The bonding between ion-pairs has covalent character 17.4% in (I) and 14.5% in (II). The values of BDEs are depends on the choice of density functionals and follow the order BP86 < PBE < PBE-D3(BJ). The contribution of orbital interactions to the total attractive interactions for the AueC(NHC*) bonds in cationic fragments [(NHC*)(2)Au](+) and [(NHC*)(2)AuCl2](+) varies from 27.8% to 36.7% and is higher for Au(III) complexes.
First author: Bae, GT, Time-Dependent Density Functional Theory Studies of Optical Propertiesg of Au Nanoparticles: Octahedra, Truncated Octahedra, and Icosahedra, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 23127, (2015)
Abstract: The optical absorption properties of gold nanopartides are investigated theoretically. A time-dependent density functional theory approach is employed to determine excitation energies for a set of three structural shapes: octahedra, truncated octahedra, and icosahedra (Au-n,functional. The n = 6-85) in several charge states that correspond to electronic shell closings. Octahedral Au-n clusters with n = 6-85, truncated octahedral Au-n clusters with n = 13-79, and icosahedral Au-n clusters with n = 13-55 are examined. The optimization calculations use the BP86/DZ.4f level of theory, and the excitation energy calculations employ the LB94 functional. The Amsterdam Density Functional code was used for all calculations.
First author: Sadhu, B, Selectivity of a Singly Permeating Ion in Nonselective NaK Channel:g Combined QM and MD Based Investigations, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 12783, (2015)
Abstract: Ion channels, such as potassium channels are known to discriminate ions to achieve remarkable selective transportation of K+ over Na+ through the membrane. The recently reported NaK ion channel, on the contrary, seems to be an exception, as it is observed to permeate most of the group IA alkali metal cations and hence is suggested to be nonselective in nature. However, does that correspond to a complete annihilation of selectivity inside the selectivity filter (SF) of the channel? What is the origin of such nonselectivity/selectivity, if any? The present computational study is an extensive multiscale modeling approach to find the probable answers to these intriguing questions. Here, we have used density functional theory (DFT) based calculations using a realistic truncated model of SF from the crystal structures of the NaK ion channel to evaluate the binding of various alkali metal ions (Na+, K+ and Cs+), free from "contamination" due to the absence any other "rivalry" cations, in its different binding sites. Among all of the possible binding sites, a vestibule is noticed to be nonselective and seen to act as a probable binding site only in the presence of multiple ions. Binding sites S3 and S4 are found to be selective for K+ and Na+, may lead to an erroneous selectivity trend as it neglects the synergetics of consecutive binding sites on the final outcome. Energy decomposition analysis revealed ion-dipole electrostatics as the major contributing interaction in metal-bound binding sites. Our investigations find that although NaK is permeable to monovalent alkali metal ions, strongly "site specific" selectivity does exist at the three well-defined noncontiguous binding sites of the SF. Different important physicomechanical parameters (such as ligating environment, synergistic influence of binding sites, and topological constraints) are found to be the determining factor to induce the "site specific" selectivity of ions during translocation. Wherever possible, our computed results are compared with the available experimental findings. We finally conduct a detailed umbrella sampling-corrected metadynamics simulation in order to obtain an ion permeation free energy landscape within the SF that corroborates well with the "site specific" selectivity trend.
First author: Goesten, MG, Six- Coordinate Group 13 Complexes: The Role of d Orbitals andg Electron-Rich Multi-Center Bonding, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 12034, (2015)
Abstract: Bonding in six-coordinate complexes based on Group 13 elements (B, Al, Ga, In, Tl) is usually considered to be identical to that in transition-metal analogues. We herein demonstrate through sophisticated electronic-structure analyses that the bonding in these Group 13 element complexes is fundamentally different and better characterized as electron-rich hypervalent bonding with essentially no role for the d orbitals. This characteristic is carried through to the molecular properties of the complex.
First author: Zhao, YY, Insights into the new Th (IV) sulfate fluoride complex: Synthesis,g crystal structures, and temperature dependent spectroscopic properties, SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 149, 295, (2015)
Abstract: Under hydrothermal condition, the decomposition of methanesulfonic acid to sulfate anion is observed, resulting in the formation of a novel thorium sulfate fluoride compound ThF2(SO4)(H2O) (1). This complex is structurally characterized by single crystal X-ray diffraction, revealing a three-dimensional structure crystallized in the monoclinic space-group P2(1)/n, where thorium cation is nine coordinated by four SO42- oxygen atoms, four bridging F-, and one H2O molecule. The crystal lattice parameters are a = 6.9065(7) angstrom, b = 6.9256(7) angstrom, c = 10.5892(11) angstrom, beta = 96.755(2)degrees, V 502.98(9) angstrom(3), Z = 4. The temperature dependent UV-Vis-NIR absorption spectra and fluorescence spectra were collected from 77 K to 300 K, where the intensities of the peaks varied as a function of temperature. The Raman vibrational spectrum of the samples collected from 100 to 2000 cm(-1) shows identical SO42- vibration modes.
First author: Liu, L, A Fluorescent 1,5-Naphthalenedisulfonate Anion-Linked Cucurbit[6]urilg Framework, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 149, 6806, (2015)
Abstract: A highly ordered 3D framework from 1,5-naphthalenedisulfonate (1,5-NDS) and cucurbit[6]uril was synthesized and structurally determined by single-crystal X-ray diffraction analysis. The crystal structure demonstrates that the 1,5-NDS anions act as linkers to connect the cucurbit[6]uril units together through C-HO hydrogen bonds between the 1,5-NDS anions and cucurbit[6]uril. Furthermore, with 1,5-NDS as the fluorophore, the fluorescence properties of the corresponding assembly structure were investigated in the solid state. Relative to that observed for 1,5-NDS, the assembly exhibited a blueshift in the fluorescence wavelength from = 406 to 340 nm along with decreased fluorescence intensity. Theoretical calculations were in good agreement with the experimental results and disclosed that the fluorescence mechanism of the assembly structure could be ascribed to the hydrogen bonds formed between the 1,5-NDS anion and cucurbit[6]uril.
First author: Wolters, LP, Selective C-H and C-C Bond Activation: Electronic Regimes as a Tool forg Designing d(10) MLn Catalysts, CHEMISTRY-AN ASIAN JOURNAL, 10, 2272, (2015)
Abstract: We wish to understand how a transition-metal catalyst can be rationally designed so as to selectively activate one particular bond in a substrate, herein, C-H and C-C bonds in ethane. To this end, we quantum chemically analyzed the activity and selectivity of a large series of model catalysts towards ethane and, for comparison, methane, by using the activation strain model and quantitative molecular orbital theory. The model catalysts comprise d(10) MLn complexes with coordination numbers n=0, 1, and 2; metal centers M=Co-, Rh-, Ir-, Ni, Pd, Pt, Cu+, Ag+, and Au+; and ligands L=NH3, PH3, and CO. Our analyses reveal that rather subtle electronic differences between bonds can be exploited to induce a lower barrier for activating one or the other, depending, among other factors, on the catalyst's electronic regime (i.e., s-regime versus d-regime catalysts). Interestingly, the concepts and design principles emerging from this work can also be applied to the more challenging problem of differentiating between activation of the C-H bonds in ethane versus those in methane.
First author: Daday, C, Chromophore-Protein Coupling beyond Nonpolarizable Models: Understandingg Absorption in Green Fluorescent Protein, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 4825, (2015)
Abstract: The nature of the coupling of the photoexcited chromophore with the environment in a prototypical system like green fluorescent protein (GFP) is to date not understood, and its description still defies state-of-the-art multiscale approaches. To identify which theoretical framework of the chromophore protein complex can realistically capture its essence, we employ here a variety of electronic-structure methods, namely, time-dependent density functional theory (TD-DFT), multireference perturbation theory (NEVPT2 and CASPT2), and quantum Monte Carlo (QMC) in combination with static point charges (QM/MM), DFT embedding (QM/DFT), and classical polarizable embedding through induced dipoles (QM/MMpol). Since structural modifications can significantly affect the photophysics of GFP, we also account for thermal fluctuations through extensive molecular dynamics simulations. We find that a treatment of the protein through static point charges leads to significantly blue-shifted excitation energies and that including thermal fluctuations does not cure the coarseness of the MM description. While TDDFT calculations on large cluster models indicate the need of a responsive protein, this response is not simply electrostatic: An improved description of the protein in the ground state or in response to the excitation of the chromophore via ground-state or state-specific DFT and MMpol embedding does not significantly modify the results obtained with static point charges. Through the use of QM/MMpol in a linear response formulation, a different picture in fact emerges in which the main environment response to the chromophore excitation is the one coupling the transition density and the corresponding induced dipoles. Such interaction leads to significant red-shifts and a satisfactory agreement with full QM cluster calculations at the same level of theory. Our findings demonstrate that, ultimately, faithfully capturing the effects of the environment in GFP requires a quantum treatment of large photoexcited regions but that a QM/classical model can be a useful approximation when extended beyond the electrostatic-only formulation.
First author: Wolters, LP, Role of Steric Attraction and Bite-Angle Flexibility in Metal-Mediatedg C-H Bond Activation, ACS CATALYSIS, 5, 5766, (2015)
Abstract: We show quantum chemically that, contrary to common believe, bulky ligands in d(10)-ML2 complexes may enhance, instead of counteract, L-M-L bite-angle bending. The resulting more flexible or even nonlinear geometry translates into lower barriers for oxidative addition of the methane C-H bond to these complexes. This follows from our quantum chemical analyses of the bonding in and reactivity of bisphosphine palladium complexes Pd(PR3)(2) with varying steric bulk, based on relativistic dispersion-corrected DFT computations in combination with the activation strain model and quantitative MO theory. Ligands that are large but to some extent flat (instead of isotropically bulky) are shown to build up relatively strong dispersion interactions between their large surfaces ("sticky pancakes") when they bend toward each other. The resulting stabilization, a form of steric attraction, favors bending and thus enhances bite-angle flexibility. This leads to surprisingly low reaction barriers for methane C-H activation by the rather congested Pd(PCy3)(2) and Pd(PPh3)(2) model catalysts. Our findings not only explain the unexpected nonlinear L-M-L angles observed in crystallographic data but also more generally demonstrate the importance of dispersion interactions in realistic catalyst complexes. Perhaps most importantly, we reveal how the concept of steric attraction can serve as a tool for tuning bite-angle flexibility and thereby the activity of catalyst complexes.
First author: Zheng, XJ, A relativistic DFT probe of energetics and structural properties ofg catalytically important macrocyclic diuranium(III) complexes, INORGANICA CHIMICA ACTA, 437, 95, (2015)
Abstract: Understanding of reaction and structural property of diuranium(III) complexes of a single ligand is essential to advancing their experimental synthesis and exploring promising applications in small molecule activation chemistry. In this work, we theoretically examined a series of diuranium(III) complexes building on the reaction of [UI3(THF)(4)] and octadentate polypyrrolic ligands (H4L1 and H4L2). At the relativistic density functional theory level, 11.2 kcal/mol energy is required to form the Pacman-like [(UI)(2)(mu(2)-I)(L-1)](-) (1) in THF solution, while only 0.5 kcal/mol for its non-classic Pacman isomer 1n. These agree with their analogues that have been experimentally proposed. A variety of chemical modification has been made for 1. The addition of one THF solvent or one iodine ion raises reaction energy by 6.8 similar to 14.5 kcal/mol, while two or more are significantly endoergic. Smaller energies of 1.4 and 7.4 kcal/mol are required when varying bridged atom (from the iodine of 1 into the THF of 2 [(UI)(2)(mu(2)-THF)(L-1)]) and lengthening ligand linker size (from ortho-phenylene of H4L1 of 1 into anthracene of H4L2 of 3 [(UI)(2)(mu(2)-I)(L-2)](-)), respectively. Eleven diuranium(III) complexes were optimized to be energetically stable. The U-U distances of 4.13 and 4.08 angstrom were calculated for 1 and 2, respectively, compared with the long one of 5.90 angstrom for 3.
First author: Feketeova, L, Photoelectron Spectra and Electronic Structures of the Radiosensitizerg Nimorazole and Related Compounds, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 9986, (2015)
Abstract: Soft X-ray photoelectron spectroscopy has been used to investigate the radiosensitizer nimorazole and related model compounds. We report the valence and C, N, and 0 is photoemission spectra and K-edge NEXAFS spectra of gas-phase nimorazole, 1-ethyl-5-nitroimidazole, and 4(5)-nitroimidazole in combination with theoretical calculations. The valence band and core level spectra are in agreement with theory. We determine the equilibrium populations of the two tautomers in 4(5)-nitroimidazole and find a ratio of 1:0.7 at 390 K. The NEXAFS spectra of the studied nitroimidazoles show excellent agreement with spectra of compounds available in the literature that exhibit a similar chemical environment. By comparing 1-methyl-5-nitroimidazole (single tautomer) with 4(5)-nitroimidazole, we are able to disentangle the photoemission and photoabsorption spectra and identify features due to each single tautomer.
First author: Saiad, A, Electronic structure and bonding analysis of transition metal sandwichg and half-sandwich complexes of the triphenylene ligand, CANADIAN JOURNAL OF CHEMISTRY, 93, 1096, (2015)
Abstract: Full geometry optimization using the BP86 and B3LYP methods has been carried out for all of the low-energy isomers of half-sandwich L3M(Tphn) (Tphn = triphenylene, M = Ti-Ni, and L-3 = (CO)(3), Cp-) and sandwich M(Tphn)(2) (Tphn = triphenylene and M = Ti, Cr, Fe, Ni) structures. Depending on the electron richness of the molecule and the nature of the metal, a complete rationalization of the bonding in triphenylene complexes has been provided. The triphenylene adopts various hapticities from eta(2) to eta(6), some of them involving full or partial coordination of the C-6 ring and shown to be quite flexible with respect to the ground spin state. The triphenylene behavior remains dependent on the electron-withdrawing and electron-donor properties of the (CO)(3)M and CpM fragments, respectively. For the sandwich complexes, both triphenylene ligands prefer to behave differently depending on the coordination mode to satisfy the metal electron demand.
First author: Chai, S, Impact of the halogenated substituent on electronic and charge transportg properties of organic semiconductors: A theoretical study, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1069, 48, (2015)
Abstract: The electronic and charge transport properties of the derivatives based on tetracene with aryl and halogenated aryl substituents have been investigated theoretically. This kind of functionalization is demonstrated to have a significant effect to stabilize the molecular orbital, densify the molecular packing, enhance the electronic coupling, and further lead to a high mobility, though it would also cause some increases in the reorganization energy. The packing modes of FPPT and PPT crystals are analyzed in details and effective coupling projected areas are put forward to understand the intermolecular interactions. Interestingly, FPPT is found to have a well-ordered packing as well as the improved hole mobility of 4.67 cm(2) V-1 s(-1). In addition, the contributions of different frequencies of vibration to the total reorganization energies are also discussed with the normal mode analysis. This study clarifies the halogenated substituent effect on transport properties and provides the guide for molecular design of novel functional materials.
First author: Muck, FM, Stable Four-Coordinate Guanidinatosilicon(IV) Complexes with SiN(3)Elg Skeletons (El=S, Se, Te) and Si=El Double Bonds, CHEMISTRY-A EUROPEAN JOURNAL, 21, 14011, (2015)
Abstract: To get information about the reactivity profile of the donor-stabilized guanidinatosilicon(II) complexes 2 and 3, a series of oxidative addition reactions was studied. Treatment of 2 and 3 with S-8, Se, or Te afforded the respective four-coordinate silicon(IV) complexes 8-10 and 12-14, which contain an SiN(3)El skeleton (El=S, Se, Te) with an Si=El double bond. Treatment of 2 with N2O yielded the dinuclear four-coordinate silicon(IV) complex 11 with an SiN3O skeleton and a central four-membered Si2O2 ring. Compounds 8-14 exist both in the solid state and in solution. They were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses. The reactivity profile of 2 was compared with that of the structurally related bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), which is three-coordinate in the solid state and four-coordinate in solution (1′). In contrast, as shown by state-of-the-art relativistic DFT analyses and experimental studies, silylene 2 is three-coordinate both in the solid state and solution. The three-coordinate species 2 is 9.3 kcal mol(-1) more stable in benzene than the four-coordinate isomer 2′. The reason for this was studied by bonding analyses of 2 and 2′, which were compared with those of 1 and 1′. The gas-phase proton affinities of the relevant species in solution (1′ and 2) amount to 288.8 and 273.8 kcal mol(-1), respectively.
First author: Donoli, A, Charge Transfer Properties of Benzo[b]thiophene Ferrocenyl Complexes, ORGANOMETALLICS, 34, 4451, (2015)
Abstract: The synthesis of 2-ferrocenylbenzo[b]-thiophene, 3-ferrocenylbenzo[b]thiophene, 1,1-bis(2-indene)-ferrocene, and the two isomers of 1,1′-bis(2-benzo[b]-thiophene)ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo[b]thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo[b]thiophenes and a comparison with indene analogues allowed an in-depth investigation on how the geometric modifications and the presence of sulfur affect their physical properties. The molecular structure of 3-ferrocenylbenzo[b]-(t)hiophene has been determined by X-ray diffraction. Electrochemistry and UV-vis-NIR spectroscopy, in particular the appearance upon oxidation of a charge transfer absorption in the NIR region, are rationalized through quantum chemistry calculations and in the framework of the Hush theory.
First author: Zhao, YL, Dissecting the bond-formation process of d(10)-metal-ethene complexesg with multireference approaches, THEORETICAL CHEMISTRY ACCOUNTS, 134, 4451, (2015)
Abstract: than palladium-ethene compounds with similar coordination spheres. The bonding mechanism of ethene to a nickel or palladium center is studied by the density matrix renormalization group algorithm, the complete active space self-consistent field method, coupled cluster theory, and density functional theory. Specifically, we focus on the interaction between the metal atom and bis-ethene ligands in perpendicular and parallel orientations. The bonding situation in these structural isomers is further scrutinized using energy decomposition analysis and quantum information theory. Our study highlights the fact that when two ethene ligands are oriented perpendicular to each other, the complex is stabilized by the metal-to-ligand double-back-bonding mechanism. Moreover, we demonstrate that nickel-ethene complexes feature a stronger and more covalent interaction between the ligands and the metal center than palladium-ethene compounds with similar coordination spheres.
First author: Berger, JA, Fully Parameter-Free Calculation of Optical Spectra for Insulators,g Semiconductors, and Metals from a Simple Polarization Functional, PHYSICAL REVIEW LETTERS, 115, 4451, (2015)
Abstract: We present a fully parameter-free density-functional approach for the accurate description of optical absorption spectra of insulators, semiconductors, and metals. We show that this can be achieved within time-dependent current-density-functional theory using a simple dynamical polarization functional. We derive this functional from physical principles that govern optical spectra. Our method is truly predictive because not a single parameter is used. In particular, we do not use an ad hoc material-dependent broadening parameter to compare theory to experiment as is usually done. Our approach is numerically efficient; the cost equals that of a calculation within the random-phase approximation.
First author: de Silva, P, Communication: A new class of non-empirical explicit density functionalsg on the third rung of Jacob's ladder, JOURNAL OF CHEMICAL PHYSICS, 143, 4451, (2015)
Abstract: We construct an orbital-free non-empirical meta-generalized gradient approximation (GGA) functional, which depends explicitly on density through the density overlap regions indicator [P. de Silva and C. Corminboeuf, J. Chem. Theory Comput. 10, 3745 (2014)]. The functional does not depend on either the kinetic energy density or the density Laplacian; therefore, it opens a new class of meta-GGA functionals. By construction, our meta-GGA yields exact exchange and correlation energy for the hydrogen atom and recovers the second order gradient expansion for exchange in the slowly varying limit. We show that for molecular systems, overall performance is better than non-empirical GGAs. For atomization energies, performance is on par with revTPSS, without any dependence on Kohn-Sham orbitals.
First author: Ceron, MR, Bis-1,3-dipolar Cycloadditions on Endohedral Fullerenes M3N@I-h-C-80 (Mg = Sc, Lu): Remarkable Endohedral-Cluster Regiochemical Control, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 11775, (2015)
Abstract: In this work, we briefly report some attempts to control regioisomeric bisadditions on Sc3N@I-h-C-80 and Lu3N@I-h-C-80 using the tether-controlled multifunctionalization method. We then describe the use of independent (nontethered) bis-1,3-dipolar cycloaddition reactions and the characterization of 5 new bisadducts, 3 for Sc3N@C-80 and 2 for Lu3N@C-80, which have never been reported before. Unexpectedly and remarkably, 4 of these compounds exhibit relatively high symmetry and 2 of these bisadducts are the first examples of intrinsically chiral endohedral compounds, due to the addition pattern, not to the presence of chiral centers on the addends. Since an analysis of the statistically possible number of bisadduct isomers on an I-h-C-80 cage has not been reported, we present it here.
First author: Yamamoto, T, Cisplatin inhibits MEK1/2, ONCOTARGET, 6, 23510, (2015)
Abstract: Cisplatin (cDDP) is known to bind to the CXXC motif of proteins containing a ferrodoxin-like fold but little is known about its ability to interact with other Cu-binding proteins. MEK1/2 has recently been identified as a Cu-dependent enzyme that does not contain a CXXC motif. We found that cDDP bound to and inhibited the activity of recombinant MEK1 with an IC50 of 0.28 mu M and MEK1/2 in whole cells with an IC50 of 37.4 mu M. The inhibition of MEK1/2 was relieved by both Cu+1 and Cu+2 in a concentration-dependent manner. cDDP did not inhibit the upstream pathways responsible for activating MEK1/2, and did not cause an acute depletion of cellular Cu that could account for the reduction in MEK1/2 activity. cDDP was found to bind MEK1/2 in whole cells and the extent of binding was augmented by supplementary Cu and reduced by Cu chelation. Molecular modeling predicts 3 Cu and cDDP binding sites and quantum chemistry calculations indicate that cDDP would be expected to displace Cu from each of these sites. We conclude that, at clinically relevant concentrations, cDDP binds to and inhibits MEK1/2 and that both the binding and inhibitory activity are related to its interaction with Cu bound to MEK1/2. This may provide the basis for useful interactions of cDDP with other drugs that inhibit MAPK pathway signaling.
First author: Loginov, DA, Cationic iridacarboranes [3-(arene)-3,1,2-IrC2B9H11](+) andg [3-(MeCN)(3)-3,1,2-IrC2B9H11](+): Synthesis, reactivity, and bonding.g Catalysis of oxidative coupling of benzoic acid with alkynes, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 793, 232, (2015)
Abstract: (Arene)iridacarboranes [3-(arene)-3,1,2-IrC2B9H11](+) (arene – benzene (1a), toluene (1b), o-xylene (1c), m-xylene (1d), durene (1e)) were synthesized by reaction of [(cod)IrCl](2) with Tl[Tl(eta-7,8-C2B9H11)] with the subsequent treatment of the anion [3-(cod)-3,1,2-IrC2B9H11](-) formed by arenes in refluxing trifluoroacetic acid. Cation 1a reacts with acetonitrile giving complex [3-(MeCN)(3)-3,1,2-IrC2B9H11](+) (2). Reactions of 2 with Cp- anions and arenes afford the cyclopentadienyl and arene derivatives 3-(eta-C5H4R)-3,1,2-IrC2B9H11 (R = H (3a), C(O)Me (3b)) and [3-(arene)-3,1,2-IrC2B9H11](+) (arene = mesitylene (1f), [2,2] paracyclophane (1g)). The structures of 1ePF(6) and 2BF(4) were determined by X-ray diffraction. According to energy decomposition analysis, the metal-benzene bonding in the iridium cation 1a is stronger than in the rhodium analog [3-(eta-C6H6)-3,1,2-RhC2B9H11](+) but weaker than in [(C5R5)Ir(C6H6)](2+). In the presence of Ag2CO3, iridacarboranes 1a and 2 catalyze the oxidative coupling of benzoic acid with diphenylacetylene selectively giving 3,4-diphenylisocoumarin in 40-50% yields. In contrast, the reactions catalyzed by [3,3-Cl-2-4-SMe2-3,1,2-IrC2B9H10](2) and [CpIrI2](2) afford only 1,2,3,4-tetraphenylnaphthalene in 10 and 35% yields, respectively. The iridium catalyzed decarboxylation of benzoic acid was analyzed by DFT calculations.
First author: Thenraj, M, Contrasting Electronic Requirements for C-H Binding and C-H Activationg in d(6) Half-Sandwich Complexes of Rhenium and Tungsten, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 1818, (2015)
Abstract: A computational study of the interaction half-sandwich metal fragments (metal=Re/W, electron count=d(6)), containing linear nitrosyl (NO+), carbon monoxide (CO), trifluorophosphine (PF3), N-heterocyclic carbene (NHC) ligands with alkanes are conducted using density functional theory employing the hybrid meta-GGA functional (M06). Electron deficiency on the metal increases with the ligand in the order NHC < CO < PF3 < NO+. Electron-withdrawing ligands like NO+ lead to more stable alkane complexes than NHC, a strong electron donor. Energy decomposition analysis shows that stabilization is due to orbital interaction involving charge transfer from the alkane to the metal. Reactivity and dynamics of the alkane fragment are facilitated by electron donors on the metal. These results match most of the experimental results known for CO and PF3 complexes. The study suggests activation of alkane in metal complexes to be facile with strong donor ligands like NHC.
First author: Xu, W, The electronic configurations of LnX (Ln = La-Eu, X = O, S, Se, Te): Ag FON-DFT investigation, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1068, 81, (2015)
Abstract: Relativistic density functional theory calculation has been carried out for lanthanide monochalcogenide molecules LnX (Ln = La-Eu, X = O, S, Se, Te). Fractional occupation number approach was applied to investigate the electronic structure. LnX are mainly ionic molecules with 5d-np (n = 2-5 for O-Te) covalent contributions. The ground state formal configuration is 4f(k)sigma(1) (k = 0-6 for La-Eu) when k <3, and 4f(k+1)sigma(0) when k >3. NdX (k = 3) molecules mostly behave as a mixture between them. Molecular orbital analysis and Mulliken population indicate orbital mixing of Ln (4f, 5d, 6s) in most molecules. Spin-orbit coupling has an increasing effect from La to Eu on bond lengths and dipole moments.
First author: Ma, ZW, First-principles study on stability and magnetism of MAln (n=2-12; M =g Cr, Mn, Fe, Co, Ni, Cu, Zn) clusters, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1068, 88, (2015)
Abstract: By using the Amsterdam Density Functional (ADF) with TZ2P basis set in conjunction with self-consistent-field (SCF), we have studied the geometric features, stabilities and magnetic properties of MAln (M = Cr, Mn, Fe, Co, Ni, Cu, Zn; n = 2-12) clusters. All the calculations have been made in the framework of the generalized gradient approximation (GGA) by means of the Becke-Perdew functional. The pronounced stabilities and magnetism of some 3d metal atom doped Al clusters can be explained by the spherical jellium model (SJM). From atom Mn to Zn, only the MAln (M = Cr, Mn, Fe; n = 2-12) clusters exhibit the large magnetic moments, especially for the MnAln (n = 2-12) clusters. And for the other MAln (M = Co, Ni, Cu, Zn; n = 2-12) clusters, only a few clusters has a total magnetic moment of less than or equal to 3 mu(B).
First author: Cazorla, C, The role of density functional theory methods in the prediction ofg nanostructured gas-adsorbent materials, COORDINATION CHEMISTRY REVIEWS, 300, 142, (2015)
Abstract: With the advent of new synthesis and large-scale production technologies, nanostructured gas-adsorbent materials (GAM) such as carbon nanocomposites and metal-organic frameworks are becoming increasingly more influential in our everyday lives. First-principles methods based on density functional theory (DFT) have been pivotal in establishing the rational design of GAM, a factor which has tremendously boosted their development. However, DFT methods are not perfect and due to the stringent accuracy thresholds demanded in modeling of GAM (e.g., exact binding energies to within similar to 0.01 eV) these techniques may provide erroneous conclusions in some challenging situations. Examples of problematic circumstances include gas-adsorption processes in which both electronic long-range exchange and nonlocal correlations are important, and systems where many-body energy and Coulomb screening effects cannot be disregarded. In this critical review, we analyze recent efforts done in the assessment of the performance of DFT methods in the prediction and understanding of GAM. Our inquiry is constrained to the areas of hydrogen storage and carbon capture and sequestration, for which we expose a number of unresolved modeling controversies and define a set of best practice principles. Also, we identify the subtle problems found in the generalization of DFT benchmark conclusions obtained in model cluster systems to real extended materials, and discuss effective approaches to circumvent them. The increasing awareness of the strengths and imperfections of DFT methods in the simulation of gas-adsorption phenomena should lead in the medium term to more precise, and hence even more fruitful, ab initio engineering of GAM.
First author: Maurer, RJ, Many-body dispersion effects in the binding of adsorbates on metalg surfaces, JOURNAL OF CHEMICAL PHYSICS, 143, 142, (2015)
Abstract: A correct description of electronic exchange and correlation effects for molecules in contact with extended (metal) surfaces is a challenging task for first-principles modeling. In this work, we demonstrate the importance of collective van der Waals dispersion effects beyond the pairwise approximation for organic-inorganic systems on the example of atoms, molecules, and nanostructures adsorbed on metals. We use the recently developed many-body dispersion (MBD) approach in the context of density-functional theory [Tkatchenko et al., Phys. Rev. Lett. 108, 236402 (2012) and Ambrosetti et al., J. Chem. Phys. 140, 18A508 (2014)] and assess its ability to correctly describe the binding of adsorbates on metal surfaces. We briefly review the MBD method and highlight its similarities to quantum-chemical approaches to electron correlation in a quasiparticle picture. In particular, we study the binding properties of xenon, 3,4,9,10-perylene-tetracarboxylic acid, and a graphene sheet adsorbed on the Ag(111) surface. Accounting for MBD effects, we are able to describe changes in the anisotropic polarizability tensor, improve the description of adsorbate vibrations, and correctly capture the adsorbate-surface interaction screening. Comparison to other methods and experiment reveals that inclusion of MBD effects improves adsorption energies and geometries, by reducing the overbinding typically found in pairwise additive dispersion-correction approaches.
First author: Hauser, SA, Iridium Complexes of the Conformationally Rigid IBioxMe(4) Ligand:g Hydride Complexes and Dehydrogenation of Cyclooctene, ORGANOMETALLICS, 34, 4419, (2015)
Abstract: A method for accessing the formally 14 VE iridium(III) hydride fragment fIr(IBioxMe,),(H)(2)}(+) (2), containing the conformationally rigid NHC ligand IBioxMe(4), is reported. Hydrogenation of trans-[Ir(IBioxMe(4))(2)(COE)C1] (1) in the presence of excess Na[BAr4F] leads to the formation of dimeric [fIr(IBioxMe(4))(2)(H)(2)Cl]-[BAr4F] (3), which is structurally fluxional in solution and acts as a reservoir of monomeric 2 in the presence of excess halogen ion abstractor. Stable dihydride complexes trans-[Ir(IBioxMe(4))(2)(2,2′-bipyridine)(H)(2)][BAr4F] (4) and [Ir(IBioxMe(4))3(H)(2)][BAr4F] (5) were subsequently isolated through in situ trapping of 2 using 2,2′-bipyridine and IBioxMe(4), respectively, and fully characterized. Using mixtures of 3 and Na[BAr4F] as a latent source of 2, the reactive monomeric fragment's reactivity was explored with excess ethylene and cyclooctene, and trans-[Ir(IBioxMe(4))(2)(C2H4)(2)][BAr4F] (6) and cis-[1r(IBioxMe(4))(2)(COD)][BAr4F] (7) were isolated, respectively, through sacrificial hydrogenation of the alkenes. Complex 6 is notable for the adoption of a very unusual orthogonal arrangement of the trans-ethylene ligands in the solid state, which has been analyzed computationally using energy and charge decomposition (EDA-NOCV). The formation of 7 via transfer dehydrogenation of COE highlights the ability to partner IBioxMe(4) with reactive metal centers capable of C H bond activation, without intramolecular activation. Reaction of 7 with CO slowly formed trans-[Ir(lBioxMe(4))(2)(CO)(2)] [BAr4F] (8), but the equivalent reaction with bis-ethylene 6 was an order of magnitude faster, quantifying the strong coordination of COD in 7.
First author: Mavrandonakis, A, Ab lnitio Study of the Adsorption of Small Molecules on Metal-Organicg Frameworks with Oxo-centered Trimetallic Building Units: The Role of theg Undercoordinated Metal Ion, INORGANIC CHEMISTRY, 54, 8251, (2015)
Abstract: The interactions of H-2, CO, CO2, and H2O with the under-coordinated metal centers of the trimetallic oxo-centered M-3(III)(mu(3)-O)(X) (COO)(6) moiety are studied by means of wave function and density functional theory. This trimetallic oxo-centered cluster is a common building unit in several metal organic frameworks (MOFs) such as MIL-100, MIL-101, and MIL-127 (also referred to as soc-MOF). A combinatorial computational screening is performed for a large variety of trimetallic oxo-centered units (M3O)-O-III (M = Al3+, Sc3+, V3+, Cr3+, Fe3+, Ga3+, Rh, In3+, Ir3+) interacting with H2O, H-2, CO, and CO2. The screening addresses interaction energies, adsorption enthalpies, and vibrational in properties. The results show that the Rh and Ir analogues are very promising so materials for gas storage and separations.
First author: Ramanantoanina, H, Prospecting Lighting Applications with Ligand Field Tools and Densityg Functional Theory: A First-Principles Account of the 4f(7)-4f(6)5d(1)g Luminescence of CsMgBr3:Eu2+, INORGANIC CHEMISTRY, 54, 8319, (2015)
Abstract: The most efficient way to provide domestic lighting nowadays is by light-emitting diodes (LEDs) technology combined with phosphors shifting the blue and UV emission toward a desirable sunlight spectrum. A route in the quest for warm-white light goes toward the discovery and tuning of the lanthanide-based phosphors, a difficult task, in experimental and technical respects. A proper theoretical approach, which is also complicated at the conceptual level and in computing efforts, is however a profitable complement, offering valuable structure property rationale as a guideline in the search of the best materials. The Eu2+-based systems are the prototypes for ideal phosphors, exhibiting a wide range of visible light emission. Using the ligand field concepts in conjunction with density functional theory (DFT), conducted in nonroutine manner, we develop a nonempirical procedure to investigate the 4f(7)-4f(6)5d(1) luminescence of Eu2+ in the environment of arbitrary ligands, applied here on the CsMgBr3:Eu2+-doped material. Providing a salient methodology for the extraction of the relevant ligand field and related parameters from DFT calculations and encompassing the bottleneck of handling large matrices in a model Hamiltonian based on the whole set of 33 462 states, we obtained an excellent match with the experimental spectrum, from first-principles, without any fit or adjustment. This proves that the ligand field density functional theory methodology can be used in the assessment of new materials and rational property design.
First author: Kvapilova, H, Electronic Excited States of Tungsten(0) Arylisocyanides, INORGANIC CHEMISTRY, 54, 8518, (2015)
Abstract: W(CNAryl)(6) complexes containing 2,6-dfisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited. states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh(OMe1))(6); CNdippPh(OMe2) = 4-(3,5-dimethoxyphenyl)-2,6-thisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198-1205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density functional theory (TDDFT); the lowest triplet state was characterized by time-resolved infrared spectroscopy (TRIR) supported by density functional theory (DFT). The intense absorption band of W(CNdipp)(6) at 460 nm and that of W(CNdippPh(OMe2))(6) at 500 nm originate from transitions of mixed pi pi*(CgN-C)/MLCT(W -> Aryl) character, whereby W is depopulat by ca. 0.4 e(-) and the electron-density changes are predominantly localized along two equatorial molecular axes. The red shift and intensity rise on going from W(CNdipp)(6) to W(CNdippPI(OMe2))(6) are attributable to more extensive delocalization of the MLCT component. The complexes also exhibit absorptions in the 300-320 nm region, owing to W -> CgN MLCT transitions. Electronic absorptions in the spectrum of W(CNXy)(6) (Xy = 2,6-dimethylphenyl), a complex with orthogonal aryl orientation, have similar characteristics, although shifted to higher energies. The relaxed lowest W(CNAryl)(6) triplet state combines pi pi* excitation of a trans pair of CgN-C moieties with MLCT (0.21 e(-)) and ligand-to-ligand charge transfer (LLCT, 0.24-0.27 el from the other four CNAryl ligands to the axial aryl and, less, to CgN groups; the spin density is localized along a single Aryl-NgC W-CgN Aryl axis. Delocalization of excited electron density on outer aryl rings in W(CNdippPh(OMe2))(6) likely promotes photoinduced electron-transfer reactions to acceptor molecules. TRIR spectra show an intense broad bleach due to upsilon(CgN), a prominent transient upshifted by 60-65 cm(-1), and a weak down-shifted feature due to antisymmetric CgN stretch along the axis of high spin density. The TRIR spectral pattern remains unchanged on the femtosecond-nanosecond time scale, indicating that intersystem crossing and electron-density localization are ultrafast (<100 fs).
First author: Lee, C, Water Splitting Processes on Mn4O4 and CaMn3O4 Model Cubane Systems, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 9325, (2015)
Abstract: Catalytic conversion of solar energy into chemical energy has been frequently investigated to develop dean energy sources in the last few decades. Metal oxide complexes show high potential for the catalytic conversion process, but the biochemical process in green plants has better efficiency than artificial photocatalysts consisting of metal oxides. In this work, the water splitting process is theoretically investigated using two synthetic model complexes whose structures are similar to the manganese-based oxygen evolving complex in photosystem II. Model A consists of four Mn atoms, and model B consists of three Mn atoms and a Ca atom in the core. Model A shows a better ability for water splitting than model B when comparing the highest reaction energy. The highest reaction energies are 2.56 and 2.99 eV for models A and B, respectively. In model B, the first oxidation in the water splitting process is exothermic, which is different from model A. In both models, the molecular oxygen generation step is endothermic by about 1.0-2.5 eV.
First author: Koch, M, Bimodal Exciplex Formation in Bimolecular Photoinduced Electron Transferg Revealed by Ultrafast Time-Resolved Infrared Absorption, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 11846, (2015)
Abstract: The dynamics of a moderately exergonic photoinduced charge separation has been investigated by ultrafast time-resolved infrared absorption with the dimethylanthracene/phthalonitrile donor/acceptor pair in solvents covering a broad range of polarity. A distinct spectral signature of an exciplex could be identified in the -CgN stretching region. On the basis of quantum chemistry calculations, the 4-5 times larger width of this band compared to those of the ions and of the locally excited donor bands is explained by a dynamic distribution of exciplex geometry with different mutual orientations and distances of the constituents and, thus, with varying charge-transfer character. Although spectrally similar, two types of exciplexes could be distinguished by their dynamics: short-lived, "tight", exciplexes generated upon static quenching and longer-lived, "loose", exciplexes formed upon dynamic quenching in parallel with ion pairs. Tight exciplexes were observed in all solvents, except in the least polar diethyl ether where quenching is slower than diffusion. The product distribution of the dynamic quenching depends strongly on the solvent polarity: whereas no significant loose exciplex population could be detected in acetonitrile, both exciplex and ion pair are generated in less polar solvents, with the relative population of exciplex increasing with decreasing solvent polarity. These results are compared with those reported previously with donor/acceptor pairs in different driving force regimes to obtain a comprehensive picture of the role of the exciplexes in bimolecular photoinduced charge separation.
First author: Dimuthu, KL, Strong Tunable Visible Absorption Predicted for Polysilo-acenes Usingg TDDFT Calculations, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 6, 3341, (2015)
Abstract: The optical properties of polysilo-acenes with two to six fused rings are studied using time-dependent density functional theory. We show that there are three spectral features in the absorption spectra analogous to alpha, beta, and p-band peaks known for carbon-based acenes. The beta peak is the most prominent feature in each spectrum, which appears in the visible region. Both alpha and beta peaks originate due to identical transitions that are polarized along the long axis of the system. The constructive interaction of quasi-degenerate configurations gives rise to the strong beta peak, while their destructive interaction results in the a peak with a low oscillator strength. Because the constructive interaction of configurations is characteristic of plasmons in acenes and noble metal nanoparticles, the beta peak can be identified as plasmonic for polysilo-acenes. The strong visible absorption and the potential for use in existing Si-technology affirm the interest in polysilo-acenes.
First author: Mavroudakis, E, On the Use of Quantum Chemistry for the Determination of Propagation,g Copolymerization, and Secondary Reaction Kinetics in Free Radicalg Polymerization, POLYMERS, 7, 1789, (2015)
Abstract: Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP) with growing interest. Nowadays, quantum chemistry (QC) can be considered a powerful and cost-effective tool for the kinetic characterization of many individual reactions in FRP, especially those that cannot yet be fully analyzed through experiments. The recent focus on copolymers and systems where secondary reactions play a major role has emphasized this feature due to the increased complexity of these kinetic schemes. QC calculations are well-suited to support and guide the experimental investigation of FRP kinetics as well as to deepen the understanding of polymerization mechanisms. This paper is intended to provide an overview of the most relevant QC results obtained so far from the investigation of FRP. A comparison between computational results and experimental data is given, whenever possible, to emphasize the performances of the two approaches in the prediction of kinetic data. This work provides a comprehensive database of reaction rate parameters of FRP to assist in the development of advanced models of polymerization and experimental studies on the topic.
First author: Kolesnikov, VI, Compatibility of chemical elements at grain boundaries in steel, DOKLADY PHYSICAL CHEMISTRY, 464, 194, (2015)
Abstract: A quantum-chemical study was performed to analyze the interaction of atoms of impurity and alloying elements with the surface of grains in steel. Atoms of elements in the first five periods of the periodic table (from hydrogen to xenon) were considered. A cluster model and a two-period slab model were used. Estimates of the compatibility of elements with iron at grain boundaries in steel were made, which agree with the known experimental data and fit the periodic low. The results of this study can be used for predicting the strength properties of polycrystalline materials into which various alloying elements are added.
First author: Kong, XQ, A solid-state O-17 NMR study of platinum-carboxylate complexes:g carboplatin and oxaliplatin, CANADIAN JOURNAL OF CHEMISTRY, 93, 945, (2015)
Abstract: We report synthesis and solid-state NMR characterization of two O-17-labeled platinum anticancer drugs: cis-diammine(1,1-cyclobutane-[O-17(4)] dicarboxylato) platinum(II) (carboplatin) and ([O-17(4)] oxalato)[(1R, 2R)-(-)-1,2-cyclohexanediamine)] platinum(II) (oxaliplatin). Both O-17 chemical shift (CS) and quadrupolar coupling (QC) tensors were measured for the carboxylate groups in these two compounds. With the aid of plane wave DFT computations, the O-17 CS and QC tensor orientations were determined in the molecular frame of reference. Significant changes in the O-17 CS and QC tensors were observed for the carboxylate oxygen atom upon its coordination to Pt(II). In particular, the O-17 isotropic chemical shifts for the oxygen atoms directly bonded to Pt(II) are found to be smaller (more shielded) by 200 ppm than those for the non-Pt-coordinated oxygen atoms within the same carboxylate group. Examination of the O-17 CS tensor components reveals that such a large (17)Ocoordination shift is primarily due to the shielding increase along the direction that is within the O=C-O-Pt plane and perpendicular to the O-Pt bond. This result is interpreted as due to the sigma donation from the oxygen nonbonding orbital (electron lone pair) to the Pt(II) empty d(yz) orbital, which results in large energy gaps between sigma(Pt-O) and unoccupied molecular orbitals, thus reducing the paramagnetic shielding contribution along the direction perpendicular to the O-Pt bond. Wefound that the O-17 QC tensor of the carboxylate oxygen is also sensitive to Pt(II) coordination, and that O-17 CS and QC tensors provide complementary information about the O-Pt bonding.
First author: Seidu, I, Applications of Time-Dependent and Time-Independent Density Functionalg Theory to Electronic Transitions in Tetrahedral d(0) Metal Oxides, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 4041, (2015)
Abstract: We present benchmark calculations on excitation energies based on time-dependent density functional theory (TDDFT) as well as orbital relaxed self-consistent and constricted variational DFT (RSCF-CV-DFT) with and without use of the Tamm-Dancoff approximation. The compilation contains results for the 3d complexes MnO4-, CrO42-, and VO43-, as well as the 4d congeners RuO4, TcO4-, and MoO42-, and 5d homologues OsO4, ReO4-, and WO42-. Considerations have been given to the local density approximation (LDA) and the functionals BP86 and PBE based on the generalized gradient approximation (GGA), as well as the hybrids B3LYP, BHLYP, and PBEO and the length corrected functional LCBP86. We find for the 3d complexes that RSCF-CV-DFT fares better than TDDFT. Thus, in the case of RSCF-CV-DFT, the average rootmean-square deviations (RMSDs) are 0.25-0.3 eV for GGAs, 0.1 eV for B3LYP, and 0.45 eV for BHLYP. TDDFT affords RiVISDs that on average range from 0.3 eV for local functionals to 0.7 eV for BHLYP with the largest fraction of Hartree-Fock (HF) exchange. TDDFT is seen to fare better among the heavier tetraoxo systems. For the 4d and 5d systems, the three functionals B3LYP, PBEO with an intermediate fraction of HF exchange, and LCBP86 have the lowest RMSD of 0.2 eV, whereas the local functionals (LDA, BP86, BPE) and BHLYP with the highest HF fraction and LCBP86* have a somewhat larger RMSD of 0.3 eV. Nearly the same performance is observed for RSCF-CV-DFT with respect to the different functionals in the case of the 4d and 5d systems. Thus, for the heavier tetraoxo systems, the two DFT schemes are comparable in accuracy.
First author: Carlson, RK, Can Multiconfigurational Self-Consistent Field Theory and Densityg Functional Theory Correctly Predict the Ground State ofg Metal-Metal-Bonded Complexes?, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 4093, (2015)
Abstract: The electronic structure of a diiron (FeFe) complex with strong metal-metal interaction and those of analogous complexes (CoCo, CoMn, CoFe, and FeMn) with much weaker metal-metal bonding are investigated with wave function-based methods and density functional theory. The delocalization and bonding between the metal centers in the diiron complex is only fully captured after inclusion of the complete set of 3d and 4d orbitals in the active space, a situation best suited for restricted active space (RAS) approaches. Truncation of the included set of 4d orbitals results in inappropriate localization of some 3d orbitals, incorrect description of the ground spin state as well as wrong spin state energetics, as compared to experiment. Using density functional theory, some local functionals are able to predict the correct ground spin states, and describe the chemical bonding and structural properties of all the metal metal complexes considered in this work. In contrast, the introduction of some exact exchange results in increased localization of 3d orbitals and wrong spin state energetics, a situation that is particularly troublesome for the diiron complex.
First author: Guda, SA, Optimized Finite Difference Method for the Full-Potential XANESg Simulations: Application to Molecular Adsorption Geometries in MOFs andg Metal-Ligand Intersystem Crossing Transients, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 4512, (2015)
Abstract: Accurate modeling of the X-ray absorption near-edge spectra ()CANES) is required to unravel the local structure of metal sites in complex systems and their structural changes upon chemical or light stimuli. Two relevant examples are reported here concerning the following: (i) the effect of molecular adsorption on 3d metals hosted inside metal-organic frameworks and (ii) light induced dynamics of spin crossover in metal organic complexes. In both cases, the amount of structural models for simulation can reach a hundred, depending on the number of structural parameters. Thus, the choice of an accurate but computationally demanding finite difference method for the ab initio X-ray absorption simulations severely restricts the range of molecular systems that can be analyzed by personal computers. Employing the FD1ViNES code [Phys. Rev. B, 2001, 63, 125120] we show that this problem can be handled if a proper diagonalization scheme is applied. Due to the use of dedicated solvers for sparse matrices, the calculation time was reduced by more than 1 order of magnitude compared to the standard Gaussian method, while the amount of required RAM was halved. Ni K-edge XANES simulations performed by the accelerated version of the code allowed analyzing the coordination geometry of CO and NO on the Ni active sites in CPO-27-Ni MOF. The Ni CO configuration was found to be linear, while Ni-NO was bent by almost 90 degrees. Modeling of the Fe K-edge XANES of photoexcited aqueous [Fe(bpy)(3)](2+) with a 100 Ps delay we identified the Fe-N distance elongation and bipyridine rotation upon transition from the initial low-spin to the final high-spin state. Subsequently, the X-ray absorption spectrum for the intermediate triplet state with expected 100 fs lifetime was theoretically predicted.
First author: Holzmann, N, Bonding situation in silicon complexes [(L)(2)(Si-2)] and [(L)(2)(Si)]g with NHC and cAAC ligands, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 792, 139, (2015)
Abstract: The equilibrium geometries of the silicon carbene complexes [(cAAC)(2)(Si-2)1, [(NHC)(2)(Si-2)1, [(cAAC)(2)(Si)], [(NFIC)(2)Sil and [(NHC-CH2-NHC)(Si)] have been calculated with gradient-corrected density functional theory (DFT) at the BP86/def2-TZVPP level of theory. A detailed bonding analysis of the five molecules was carried out with the NBO method and with the help of the EDA-NOCV method which provides a detailed and quantitative insight into the nature of the interactions between Sin and the carbene ligands. The silicon atom in L2Si is more strongly bonded than diatomic Si-2 in L2Si2. The cAAC ligands are stronger donors and stronger acceptors than NHC. The relative contribution of the cAAC Sin cAAC TLbackdo nation to the total orbital interactions is higher than the NHC < Sin > NHC 7-backdonation which agrees with the general assessment that cAAC is a stronger 7-acceptor than NHC. Silicon-carbene bonding in [(NHC CH2 NHC)(Si)] is stronger than in [(NHC)(2)Sil mainly because of stronger 7-backdonation but weaker than in [(cAAC)(2)(Si)]. The calculated charge distribution of the NBO method agrees with the EDA-NOCV data.
First author: Jin, X, Structure and bonding in a bimetallic endohedral cage, [Co-2@Ge-16](z-), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 792, 149, (2015)
Abstract: We report here mass spectrometric evidence for the new bimetallic cluster, [Co-2@Ge-16](z) which is observed as a mono-anion in the mass spectrum but as a tetra-anion in the solid state. Density functional theory suggests that at both oxidation levels it adopts a D-2h-symmetric structure based on two pentagonal bipyramids. The 3-connected vertices of the cage are characteristic of an electron-precise (5n = 80) count, but assigning 80 of the 86 valence electrons to the cage would imply an unrealistic degree of charge separation. We resolve this dilemma by showing that many of the electron pairs fulfill a dual role, contributing to the stable 80-electron count at the cage and to the 18-electron count at each metal. Thus it is not possible in this case to partition the charge into mutually exclusive subsets on the metal and on the cluster.
First author: Goncalves, IS, Comparing spectroscopic and electrochemical properties of complexes ofg type Cp'M(eta(3)-C3H5)(CO)(2) (Cp' = Cp, Ind, Flu): A complementaryg experimental and DFT study, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 792, 154, (2015)
Abstract: A series of allyl complexes of the general formula [Cp'Mo(eta(3)-C3H5)(CO)(2)], where Cp' = Cp, CpMe, Cp*, Ind, IndMe, IndMe2, Flu, and three tungsten analogues, has been prepared and characterized by H-1, C-13, and Mo-95 NMR, cyclic voltammetry, and the structure of [IndMo(eta(3)-C3H5)(CO)(2)] was determined by Xray single crystal analysis. Two conformers, corresponding to the two extreme orientations of the allyl ligand (endo and exo), have been identified in solution by H-1 and Mo-95 NMR for all the complexes, except for [FluMo(eta(3)-C3F15)(CO)(2)], which only presents an exo conformation in solution.
First author: Cardoso, BD, Preference for sulfoxide S- or O-bonding to 3d transition metals – DFTg insights, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 792, 167, (2015)
Abstract: Complexes of 3d transition metals with sulfoxide ligands bound by sulfur were searched on the Cambridge Structural Database. DFT calculations reproduced the experimental geometries and the lowest energy isomer (S or O bound) matched the experimentally observed one. Distances, Wiberg indices and charges (Mulliken, Atomic Polar Tensor and Natural Population Analysis) were compared, showing an elongation and weakening of the S-O bond with O-coordination. Metal charges became more positive with 0-coordination, accompanied by a more negative sulfur charge. Examples of 0-bound sulfoxides were studied for comparison. An Energy Decomposition Analysis was performed in a series of more relevant complexes, in order to compare the two isomers and identify the reason for the structural preference. In complexes with one S-bound sulfoxide, the attractive interaction terms (electrostatic and orbital) compensate the large Pauli repulsion by a larger amount in the S- than in the 0-bound isomer. In the complex with O-bound sulfoxide this tendency was reversed by a very large reorganization energy (to bring fragments from their preferred geometry to the geometry they have in the complex). In the complexes with two ligands, S,S or 0,0 binding was preferred, and in one example they coexist. The mixed S,O coordination type led to a large orbital stabilization, but required large reorganization energies.
First author: Bharathi, K, Structural, electronic and magnetic properties of some early vs lateg transition dimetallaborane clusters – A theoretical investigation, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 792, 220, (2015)
Abstract: The strength of DFT methods in analyzing the electronic and magnetic properties of a series of dimetallaboranes of varied stoichiometry and architectural core, namely M2B3, M2B4 and M2B5 with both early-and late-transition metals is demonstrated. In particular, the observed H-1 and B-11 chemical shifts of most of the studied compounds are reproduced with a good accuracy of a few ppm at the DFT-GIAO BP86/TZ2P/SC level for the compounds with first-row transition metal elements and at the B3LYP/TZ2P/SO level for those with second-and third-row transition metal elements. This allows structural applications in elucidating the number and the location of bridging hydrogen atoms in experimentally poorly characterized metallaboranes such as (Cp*Cr)(2)B4H8.
First author: Shi, YR, A theoretical study about three organic semiconductor based ong oligothiophenes, JOURNAL OF ATOMIC AND MOLECULAR SCIENCES, 6, 179, (2015)
Abstract: Three derivatives based on oligothiophenes were theoretically investigated about the electronic and charge transport properties using density functional (DFT) theory based on the Marcus-Hush theory. The predicted highest hole mobility is 0.218 cm(2)V(-1)s(-1), and the highest electron mobility is 0.373 at 300 K. The calculated data demonstrated that the compound 1 should be a high-performance n-type organic material candidate and compound 3 may well be potential p-type materials with high mobility values. Our work also indicates that the face-to-face pi-pi interaction and S-S interactions is favorable for the molecular stacking and charge transport behaviors. The calculated results provide an additional possibility to be able to improve the origin semiconductor performance and design new electronic devices.
First author: Francisco, H, Dissociation of N2O promoted by Rh-6 clusters. A ZORA/DFT/PBE study, JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 406, 238, (2015)
Abstract: The interaction of Rh-6 clusters with the nitrous oxide (N2O) molecule was studied by means of density functional theory (DFT) calculations through the zero-order-regular approximation (ZORA), which includes relativistic effects explicitly. The purpose of this work is to characterize the N2O reduction to N-2 and O by Rhs clusters. The identified low-lying and degenerate states of Rh-6, octahedron with multiplicities of I and 7, and a triangular prism with a septet, present many active sites of reduction. The initial steps of the N2O + Rh-6 reaction were studied through different adsorption modes, each one having different multiplicities. The Rh Rh bonds define the active sites to produce N2O dissociation. The most successful reaction pathway originates when the linear N=N-O molecule is approached parallel to the Rh Rh bonds, being this active site the most numerous in the systems. The N-O bond breaks in five addressed multiplicities, with 2 and 3 degenerate energy cases in the octahedron. Other approaches studied are: N2O pointing toward the triangular or square face bisectors or to the surface between two Rh Rh bonds. In these two cases, the N2O molecule moves toward one of the Rh Rh bonds dissociating over it. Overall, to reduce N2O, the prism structure presents a greater number of different active sites, but the octahedron has more edges, in which the oxide can break. For each calculation, many parameters were obtained and are included in the text: vibrational frequencies, distances between atoms, binding energies, total electronic charges, as well as optimized geometries. An important result of this work is the feature that Rh-6 is the smallest nanoparticle having several structures at the ground state, which greatly increases the number of active sites being able to reduce the nitrous oxide contaminant.
First author: Zhang, SF, Rational design of bio-inspired high-performance ambipolar organicg semiconductor materials based on indigo and its derivatives, ORGANIC ELECTRONICS, 24, 12, (2015)
Abstract: Indigoids have received much attention as the candidates of sustainable ambipolar organic semiconductor. However, the low charge carrier mobilities extremely limit their practical applications. Therefore, in-depth understanding of their electronic-structure properties and rational molecular modifications are urgently required. Here, we propose a promising strategy to design ambipolar organic semiconductors based on indigo fragments. Moreover, we predicted the organic crystal structures by evolutionary algorithm combined with DFT-D method. Charge transport properties have been significantly improved for the designed molecules, such as narrower energy gaps, higher electron affinity, larger transfer integrals as well as much smaller reorganization energies for hole and electron. Thusly, remarkable ambipolar charge transport behavior has been predicted, for example, the charge carrier mobilities are up to mu(h)/mu(e) = 7.71/5.42 cm(2) V-1 s(-1) for NN-indigo-6,6′-2CN and mu(h)/mu(e) = 5.15/2.13 cm(2) V-1 s(-1) for C-9-NN-indigo-6,6′-2CN respectively.
First author: Mehmood, U, Hybrid TiO2-multiwall carbon nanotube (MWCNTs) photoanodes for efficientg dye sensitized solar cells (DSSCs), SOLAR ENERGY MATERIALS AND SOLAR CELLS, 140, 174, (2015)
Abstract: Dye sensitized solar cells (DSSCs) based on TiO2/MWCNTs composite with varying concentrations of CNTs (0, 0.03, 0.06, 0.09, 0.15, and 0.21 wt%), fabricated using N3 dye as a sensitizer. Transmission electron microscopy was used to confirm the dispersion of carbon nanotubes in TiO2. UV-visible absorption spectroscopy, photocurrent-voltage characteristics, and electrochemical impedance spectroscopic measurements were conducted to characterize the DSSCs. The results show that the photo conversion efficiency is highly dependent on the concentration of CNTs in the photoanode. A solar cell based on a photoanode containing 0.03 wt% MWCNTs has a power conversion efficiency which is about 30% greater than that of the unmodified photoanode. A quantum modeling technique based on the density functional theory was used to investigate the thermodynamic aspects of the charge transport processes in DSSCs. Simulation results support the experimental data.
First author: Fernando, A, Ligand Exchange Mechanism on Thiolate Monolayer Protected Au-25(SR)(18)g Nanoclusters, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 20179, (2015)
Abstract: Ligand exchange reactions are important to functionalize and modify the optical and electronic properties of thiolate-protected gold nanoparticles. A theoretical investigation of the kinetics of the ligand exchange process was performed for the Au-25(SH)(18)(-) nanoduster with CH3SH as the incoming thiol ligand. Three possible ligand exchange sites were investigated: between the core gold atom and the terminal -SH unit, between the staple gold atom and the terminal -SH unit, and between a staple gold atom and the central -SH unit. We found that the most favorable ligand exchange takes place between terminal -SH units and staple gold atoms.
First author: Smalley, AP, Mechanistic Insights into the Palladium-Catalyzed Aziridination ofg Aliphatic Amines by C-H Activation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 10632, (2015)
Abstract: Detailed kinetic studies and computational investigations have been performed to elucidate the mechanism of a palladium-catalyzed C-H activation aziridination. A theoretical rate law has been derived that matches with experimental observations and has led to an improvement in the reaction conditions. Acetic acid was found to be beneficial in controlling the formation of an off-cycle intermediate, allowing a decrease in catalyst loading and improved yields. Density functional theory (DFT) studies were performed to examine the selectivities observed in the reaction. Evidence for electronic-controlled regioselectivity for the cyclopalladation step was obtained by a distortion interaction analysis, whereas the aziridination product was justified through dissociation of acetic acid from the palladium(IV) intermediate preceding the product-forming reductive elimination step. The understanding of this reaction mechanism under the synthesis conditions should provide valuable assistance in the comprehension and design of palladium-catalyzed reactions on similar systems.
First author: Zhao, LL, Reaction Mechanism of the Symmetry-Forbidden [2+2] Addition of Ethyleneg and Acetylene to Amido-Substituted Digermynes and Distannynesg Ph2N-EE-NPh2, (E=Ge, Sn): A Theoretical Study, CHEMISTRY-A EUROPEAN JOURNAL, 21, 12405, (2015)
Abstract: Quantum chemical calculations of reaction mechanisms for the formal [2+2] addition of ethylene and acetylene to the amido-substituted digermyne and distannyne Ph2N-EE-NPh2 (E=Ge, Sn) have been carried out by using density functional theory at the BP86/def2-TZVPP level. The nature and bonding situations were studied with the NBO method and with the charge and energy decomposition analysis EDA-NOCV. The addition of ethylene to Ph2N-EE-NPh2 takes place through an initial [2+1] addition to one metal atom and consecutive rearrangement to four-membered cyclic species, which feature a weak E-E bond. Rotation about the C-C bond with concomitant rupture of the E-E bond leads to the 1,2-disubstituted ethanes, which have terminal E(NPh2) groups. The overall reaction Ph2N-EE-NPh2+C2H4 ->(Ph2N)E-C2H4-E(NPh2) has very low activation barriers and is slightly exergonic for E=Ge but slightly endergonic for E=Sn. The analysis of the electronic structure shows that there is charge donation of nearly one electron to the ethylene moiety already in the first part of the reaction. The energy partitioning analysis suggests that the HOMO(Ph2N-EE-NPh2)-> LUMO(C2H4) interaction has a similar strength as the HOMO(C2H4)-> LUMO(Ph2N-EE-NPh2) interaction. The [2+2] addition of acetylene to Ph2N-EE-NPh2 also takes place through an initial [2+1] approach, which eventually leads to 1,2-disubstituted olefins (Ph2N)E-C2H2-E(NPh2). The formation of the energetically lowest lying conformations of cis-(Ph2N)E-C2H2-E(NPh2), which occurs with very low activation barriers, is clearly exergonic for the germanium and the tin compound. The trans-coordinated isomers of (Ph2N)E-C2H2-E(NPh2) are slightly lower in energy than the cis form but they are separated by a substantial energy barrier for the rotation about the C-C bond. The energy decomposition analysis indicates that the initial reaction takes place under formation of electron-sharing bonds between triplet fragments rather than HOMO-LUMO interactions.
First author: Luo, YF, Exploration of phosphorescent platinum(II) complexes functionalized byg distinct main-group units to search for highly efficient blue emittersg applied in organic light-emitting diodes: A theoretical study, INORGANICA CHIMICA ACTA, 435, 109, (2015)
Abstract: In this study, five cyclometalated Pt(II) complexes were chosen as research subjects to investigate the effects of main-group moieties on the electronic structure, photophysical properties and radiative deactivation processes of the phosphorescent metal complexes. Density functional theory (DFT)/time-dependent DFT investigation was conducted to gain a better understanding of the properties of these Pt(II) complexes, including the ground and triplet state geometries, absorption spectra and emission wavelength. Moreover, the self-consistent spin-orbit coupling TDDFT (SOC-TDDFT) was used to calculate zero-field splitting (ZFS), radiative rate and radiative lifetime to unveil the radiative deactivation processes for these complexes. The results reveal that the different main-group moieties added on the 40-position of the phenyl ring in [Pt(ppy)(acac)] could not only dramatically affect molecular and electronic structure, absorption and luminescence properties, but also radiative deactivation processes. And the emission wavelengths of five complexes are in the range from 434 to 562 nm. Furthermore, among the studied complexes, the designed complex 4 shows great potential to serve as an efficient deep-blue-light emitter in OLED.
First author: Abreu, MB, Making sense of the conflicting magic numbers in WSin clusters, JOURNAL OF CHEMICAL PHYSICS, 143, 109, (2015)
Abstract: First principles studies on the geometric structure, stability, and electronic structure of WSin clusters, n = 6-16, have been carried out to show that the observed differing "magic sizes" for WSin clusters are associated with the nature of the growth processes. The WSi12 cluster, observed as a magic species in experiments reacting transition metal ions with silane, is not stable due to a filled shell of 18 electrons, as previously proposed, but due to its atomic structure that arrests further growth because of an endohedral transition metal site. In fact, it is found that all of these clusters, n = 6-16, have filled 5d shells except for WSi12, which has a 5d(8) configuration that is caused by crystal field splitting. The stability of WSi15+, observed as highly stable in clusters generated by vaporizing silicon and metal carbonyls, is shown to be associated with a combination of geometric and electronic features. The findings are compared with previous results on CrSin clusters.
First author: Nguyen, TT, Evaluation of Mo-95 Nuclear Shielding and Chemical Shift of [Mo6X14](2-)g Clusters in the Liquid Phase, INORGANIC CHEMISTRY, 54, 7673, (2015)
Abstract: [Mo6X14](2-) octahedral molybdenum clusters are the main building blocks of a large range of materials. Although Mo-95 nuclear magnetic resonance was proposed to be a powerful tool to characterize their structural and dynamical properties in solution, these measurements have never been complemented by theoretical studies which can limit their interpretation for complex systems. In this Article, we use quantum chemical calculations to evaluate the Mo-95 chemical shift of three clusters: [Mo6Cl,4](2-), [Mo6Br14](2-), and [Mo6I14](2-). In particular, we test various computational parameters influencing the quality of the results: size of the basis set, treatment of relativistic and solvent effects. Furthermore, to provide quantum chemical calculations that are directly comparable with experimental data, we evaluate for the first time the Mo-95 nuclear magnetic shielding of the experimental reference, namely, MoO42- in aqueous solution. This is achieved by combining ab initio molecular dynamics simulations with a periodic approach to evaluate the Mo-95 nuclear shieldings. The results demonstrate that, despite the difficulty to obtain accurate Mo-95 chemical shifts, relative values for a cluster series can be fairly well-reproduced by DFT calculations. We also show that performing an explicit solvent treatment for the reference compound improves by similar to 50 ppm the agreement between theory and experiment. Finally, the standard deviation of –,70 ppm that we calculate for the Mo-95 nuclear shielding of the reference provides an estimation of the accuracy we can achieve for the calculation of the Mo-95 chemical shifts using a static approach. These results demonstrate the growing ability of quantum chemical calculations to complement and interpret complex experimental measurements.
First author: Rohrmuller, M, The Cu2O2 torture track for a real-life system: [Cu-2(btmgp)(2)O-2](2+)g oxo and peroxo species in density functional calculations(dagger), JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 1672, (2015)
Abstract: Density functional theory (DFT) calculations of the equilibrium geometry, vibrational modes, ionization energies, electron affinities, and optical response of [Cu-2(btmgp)(2)(-O)(2)](2+) (oxo) and [Cu-2(btmgp)(2)(-(2):(2)-O-2)](2+) (peroxo) are presented. Comprehensive benchmarking shows that the description of the oxo-peroxo energetics is still a torture track for DFT, but finds the molecular geometry to be comparatively robust with respect to changes in the exchange-correlation functionals and basis sets. Pure functionals favor the oxo core found experimentally, whereas hybrid functionals shift the bias toward the peroxo core. Further stabilization of peroxo core results from relaxing the spin degrees of freedom using the broken-symmetry (BS) approach. Dispersion effects, conversely, tend to favor the oxo configuration. Triple-zeta basis sets are found to represent a sensible compromise between numerical accuracy and computational effort. Particular attention is paid to the modification of the electronic structure, optical transitions, and excited-state energies along the transition path between the oxo and peroxo species. The excited-state potential energy surface calculations indicate that two triplet states are involved in the transition that stabilize the BS solution. Charge decomposition and natural transition orbital analyses are used for obtaining microscopic insight into the molecular orbital interactions. Here, the crucial role of guanidine -interactions is highlighted for the stabilization of the Cu2O2 core.
First author: Landman, M, E versus Z isomers of Fischer aminocarbene complexg [Mo(CO)(4)(PPh3){C(NHCy)(2-furyl)}]: N-H center dot center dot centerg dot O versus C-H center dot center dot center dot O intramolecularg hydrogen bonds,JOURNAL OF MOLECULAR STRUCTURE, 1094, 36, (2015)
Abstract: A density functional theory (DFT) calculated conformation analysis of the twelve possible conformations of [Mo(CO)(4)(PPh3){C(NHCy)(2-furyl)}], 1, utilizing different DFT methods, showed that both the cis-syn,Z (2), 1-Z, and the cis-syn,Z (2), 1-E, conformations of this aminocarbene complex have similar electronic and Gibbs free energies. The solid-state crystal structure of the 1-Z is presented in this study and compared to the structure of the 1-E conformation. The stability of 1-Z, versus the previously published solid-state structure of conformer 1-E, is ascribed to stabilization of the N-H center dot center dot center dot O-Fu intramolecular bond. This is evidenced by a shorter H center dot center dot center dot O intramolecular bond in the experimental crystal structure of 1-Z. The stability of the 1-Z and 1-E conformations were analyzed and compared by density functional theory, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) methods. The NBO analysis reveals similar but stronger donor-acceptor interactions in 1-Z than in 1-E. QTAIM calculations indicate 6 and 5 bond critical points related to intramolecular bonds stabilizing the orientation of 2-furyl and NHCy in 1-Z and 1-E respectively.
First author: Stojanovic, M, The effect of steric repulsion on the torsional potential of n-butane: ag theoretical study, TETRAHEDRON, 71, 5119, (2015)
Abstract: The origin of the rotational barriers in n-butane and gauche conformational energy, the prototypes of steric repulsion, has been re-examined by using energy decomposition analysis. The Pauli repulsion was found to be an important factor, but not the source of the barriers and gauche/anti energy difference. Rather, it should be considered as a driving force for structural changes accompanying the rotation. The repulsion (steric) energy partly transfers into the deformation energy of ethyl fragments and also affects a decrease in electrostatic, orbital and dispersion interactions by inducing the structural changes, particularly the central CC bond lengthening, while it becomes less destabilizing during the anti-butane rotation.
First author: Plessow, PN, Selective Carbon-Carbon Bond Activation of Oxirane by a Bisphosphineg Pt(0) Complex-A Theoretical Study, ORGANOMETALLICS, 34, 3764, (2015)
Abstract: Platinum(0) complexes with the chelate ligand bis(di-tert-butylphosphino)methane, (Bu2P)-Bu-t-CH2-(PBu2)-Bu-t (dtbpm), generated in solution from appropriate precursors, are the only known transition metal species that selectively activate epoxides (codranes) by inserting the Pt fragment into their carbon-carbon bond. The mechanism of this unprecedented reaction is studied theoretically using the random phase approximation. We find that the reaction is kinetically controlled and is caused by the formation of a monocoordinate (dtbpm-kappa P-1)Pt(0) fragment rather than a (dtbpm-kappa P-2)Pt(0) chelate complex. Insertion into epoxide C-C bonds occurs without energy barrier. Conceivable competing reactions, oxirane C-O and C-H activation, both proceed via formation of a sigma-complex, followed by small but significant barriers for insertion steps. A reversible formation of the sigma-complexes would perfectly explain the observed reactivity. For an irreversible formation, we find that intramolecular rearrangement of these sigma-complexes toward C-C activation products is faster than both C-O and C-H activation. In principle, the same reactivity should be expected for other monocoordinated platinum(0) phosphine complexes. However, only the specific properties of dtbpm cause the subsequent, rapid, and irreversible closing of the chelate ligand yielding stable, square-planar Pt(II) C-C activation products.
First author: Oeschger, RJ, Gas-Phase Investigations on the Transmetalation Step in Sonogashirag Reactions, ORGANOMETALLICS, 34, 3888, (2015)
Abstract: The microscopic reverse of the transmetalation step in the Pd/M (M = Cu, Ag, Au) catalyzed Sonogashira-type reactions has been observed in the gas phase upon collision-induced dissociation (CID) of the heterobimetallic complexes. Measuring the activation energies by quantitative energy-resolved CID experiments provides an upper bound for the internal rearrangement energies. The potential-energy surface is investigated by density functional theory calculations and compared to the experimental values.
First author: Ponzi, A, Photoionization of endohedral atoms: Molecular and interchannel-couplingg effects, PHYSICAL REVIEW A, 92, 3888, (2015)
Abstract: Calculations of the photoionization cross section of the 2p and 3s subshells of free Ar and Ar@C-60 as examples have been performed using the molecular structure of the confined system and time-dependent density functional theory for the dynamical quantities. The results for Ar 2p in the combined system exhibit significant confinement resonances with the lower-energy ones being quite sharp, in contrast to the results of jellium-model calculations. In addition, calculations done with and without interchannel coupling between the photoionization channels of the 2p subshell of the Ar atom and the 1s subshell of the C-60 shell show that, in this case, the coupling is of negligible importance, even though the C 1s cross section is more than an order of magnitude larger than that of Ar 2p in the 300 eV range. The Ar 3s, which is not hybridized, also exhibits confinement resonances, but is very strongly affected by interchannel coupling with photoionization channels from the C-60 shell. The phenomenology of both 2p and 3s subshells is explained in terms of the interchannel-coupling matrix elements. These results should be applicable to inner-shell ionization of essentially any endohedral fullerene system.
First author: Mehmood, U, Co-sensitization of TiO2-MWCNTs hybrid anode for efficientg dye-sensitized solar cells, ELECTROCHIMICA ACTA, 173, 607, (2015)
Abstract: Co-sensitization of dyes on hybrid TiO2- MWCNTs photoanode is an effective approach to enhance the performance of a dye-sensitized solar cell (DSSC). In this work, N719 sensitizer is co-sensitized with N3. The co-sensitized device showed enhanced V-OC and J(SC) in comparison to single-dye sensitized devices. Upon optimization, the device made of the 0.1Mm N-3 + 0.4 mM N719 yielded J(SC) = 12.5 mA cm (2), V-oc = 0.73 V, FF = 0.45 and eta = 4.1 %. This performance is superior to that of either of the individual DSSCs sensitized with N3 (3.69%) and N719 (3.51 %) under the same conditions of fabrication. The efficiency of DSSCs was further improved to 4.46% by the incorporation of MWCNTs in TiO2. The hybrid TiO2/MWCNTs photoanodes with different concentrations of CNTs (0.04. 0.08, 0.12, 0.16 wt. %) were prepared using mixing technique. The optimized molar ratio of N3/N719 was used for the sensitization of hybrid photonodes. Density functional theory (DFT) was used to compute the band gaps of TiO2 and CNT-TiO2 clusters.
First author: Nowak, P, Determination of acid dissociation constants of warfarin andg hydroxywarfarins by capillary electrophoresis, JOURNAL OF PHARMACEUTICAL AND BIOMEDICAL ANALYSIS, 112, 89, (2015)
Abstract: In this work the acid dissociation constants – pK(a) of warfarin and its all important oxidative metabolites have been determined by capillary electrophoresis-based methods. It has resulted in a complete description of two acid-base dissociation equilibria, yet not investigated experimentally for phase I metabolites of warfarin. The capillary electrophoresis (CE) method based on the relation between effective electrophoretic mobilities and pH has proven to be a suitable tool for pKa determination, while the spectrophotometric (CE-DAD) and the internal standard methods (IS-CE), have appeared to be promising alternative approaches. The CE-DAD approach based on the change in absorbance spectra between the acidic and basic forms is a combination between capillary electrophoresis and spectrophotometric titration, and yields very consistent values of pK(a1) with CE. The IS-CE, in turn, enables an estimation of pK(a1) and pK(a2) from only two analytical runs, however, less accurate than CE and CE-DAD. The Debye-Huckel model has been confirmed experimentally as a good predictor of pKa values at various ionic strengths. Therefore, it has been used in determination of thermodynamic pK(a1) and pK(a2), referring to the zero ionic strength. The results are important from the analytical, pharmacological, and theoretical points of view.
First author: Breton, GW, \ Substituted 2-(Dimethylamino)biphenyl-2 '-carboxaldehydes asg Substrates for Studying n ->pi* Interactions and as a Promisingg Framework for Tracing the Burgi-Dunitz Trajectory, JOURNAL OF ORGANIC CHEMISTRY, 80, 7375, (2015)
Abstract: The Burgi-Dunitz trajectory traces points along the pathway of bond formation between a nucleophile and electrophile. Previous X-ray crystallographic studies of some molecules containing a nucleophilic nitrogen atom and electrophilic carbonyl group provided some initial evidence for various degrees of bond formation via initial n ->pi* interactions. Observation of a complete set of points along the trajectory, however, has not yet been attained. In this paper, we present a DFT computational study investigating substituted 2-(dimethylamino)biphenyl-2′-carboxaldehydes as substrates for further examination of n ->pi* interactions and as a potential framework for more complete tracing of the Burgi-Dunitz trajectory. These compounds are particulary suitable for study because of the rotational freedom granted by the C-C bond connecting the two aromatic rings allowing the molecule to choose the degree of interaction between the two complementary groups. The extent of interaction is measured by interatomic distance, NBO second-order perturbative analysis energies, volume of transferred electron density as provided by ETS-NOCV analysis, and differences in energies between models that allow for n ->pi* interactions and those that do not. A series of substituted biphenyls are ultimately identified as future synthetic targets that have maximum potential for providing improved tracing of the Burgi-Dunitz trajectory.
First author: Fihey, A, Toward an Enhancement of the Photoactivity of Multiphotochromic Dimersg Using Plasmon Resonance: A Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 6, 3067, (2015)
Abstract: Building dimers of organic photochromic compounds paves the way to multifunctional switches, but such architectures often undergo partial photoreactivity only. Combining photochromism of molecules and plasmon resonance of gold nanoparticles (NPs) is known to affect the photochromism of monomers, yet the impact on multimers remains unknown. Here we propose a theoretical study of dimers of dithienylethenes by the mean of a hybrid calculation scheme (discrete-interaction model/quantum mechanics). We aim to assess how the optical properties of multiphotochromes are tuned by the influence of the plasmon resonances. We show that, for a typical chemisorption orientation on the NP, the absorption bands responsible for the photochromism are significantly enhanced for both the doubly open and mixed closed-open isomers of the dyad, hinting that plasmon resonance could be used to boost the generally poor photoactivity of dithienylethene dyads.
First author: Jiang, N, Theoretical Studies on Hexanuclear Oxometalates [M6L19](q-) (M = Cr, Mo,g W, Sg, Nd, U). Electronic Structures, Oxidation States, Aromaticity, andg Stability, INORGANIC CHEMISTRY, 54, 7171, (2015)
Abstract: We here report a systematic theoretical study on geometries, electronic structures, and energetic stabilities of six hexanuclear polyoxometalates [M6O19](2-) of the six-valence-electron metals including the d-elements M = Cr, Mo, W, Sg from group 6 and the f-elements M = Nd, U. Scalar relativistic density functional theory was applied to these clusters in vacuum and in solution. It is shown that the O-h Lindqvist structure of the isolated [M6O19](2-) units with hexavalent M elements (M+6) is only stable for the three heavy transition metals M = Mo, W, and Sg. The rare T-h symmetry is predicted for M = U both in vacuum and in solution, owing to pseudo-Jahn-Teller distortion of these closed-shell systems. The O-h and T-h structures correspond to cyclic "aromatic" U+O-U and alternating U-O-U bonding of cross-linked U4O4 rings, respectively. The reduced [U6O19](8-) duster with pentavalent U+5 also shows T-h symmetry in vacuum, but O-h symmetry in a dielectric environment. The occurrence of different structures for varying fractional oxidation states in different environments is rationalized. Theoretical investigation of the recently synthesized U+5 complex [U6O13L6](0) (L-6 = tetracydopentadienyl dibipyridine) shows a distorted T-h-type symmetry, too. The stabilities of these complexes of different metal oxidation states are consistent with the general periodic trends of oxidation states.
First author: Du, WGH, Broken Symmetry DFT Calculations/Analysis for Oxidized and Reducedg Dinuclear Center in Cytochrome c Oxidase: Relating Structures,g Protonation States, Energies, and Mossbauer Properties in ba(3) Thermusg thermophilus,INORGANIC CHEMISTRY, 54, 7272, (2015)
Abstract: The Fe-a3(3%)center dot center dot center dot Cu-B(2+) dinuclear center (DNC) structure of the as-isolated oxidized ba(3) cytochrome c oxidase (CcO) from Therms-thermophilus (Tt) is still not fully understood. When the proteins are initially crystallized in the oxidized state, they typically become radiolyticly reduced through X-ray irradiation. Several X-ray crystal structures of reduced ba(3) CcO from Tt are available. However, depending On whether the crystals were prepared in a lipidic cubic phase environment or in detergent micelles, and whether the CcO's were chemically or radiolyticly reduced, the X-ray diffraction analysis of the crystals showed different Fe-a3(2+)center dot center dot center dot-Cu-B(+) DNC structures. On the other hand, Mossbauer spectroscopic experiments on reduced and Oxidized ba(3) CcOs from Tt (Zimmermann et al., Proc. Natl. Acad. Sei. USA 1988, 85, 5779-5783) revealed multiple Fe-57(a3)2+ and Fe-57(a3)3+ components. Moreover, one of the Fe-57(a3)3+ components observed at 4.2 K transformed from a proposed "low-spin" state to a different high-spin species when the temperature was increased above 190 K, whereas the other high-spin. Fe-57(a3)3+ component remained unchanged. In the current Article; in order to understand the heterogeneities of the DNC in both Mossbauer spectra and X-ray crystal structures, the span crossover of one of the Fe-57(a3)3+ components, and how the coordination and spin states of the Fe-a3(3+/2+) and Cu2+/1+ sites relate to the heterogeneity of the DNC structures, we have applied density functional OLYP calculations to the DNC clusters established based on the different X-ray crystal structures of ba3 CcO from Tt. As a result, specific oxidized and reduced DNC structures related to the observed Mossbauer spectra and to spectral changes with temperature have been proposed. Our calculations also show that, in certain intermediate states, the His233 and His283 ligand side chains may dissociate from the Cu-B(+) site, and they may become potential proton loading sites during the catalytic cycle.
First author: Alegret, N, Different Factors Govern Chlorination and Encapsulation in Fullerenes:g The Case of C-66, INORGANIC CHEMISTRY, 54, 7562, (2015)
Abstract: C-66 is one of the smallest fullerenes that is able to encapsulate more than one metal atom, as in Sc-2@C-66, as well as to get chlorinated at a low level, C66Cl10 or C66Cl6. We show here, with the help of computations at density functional theory level, that these two means of obtaining derivatives of non-isolated pentagon rule fullerenes are dictated by different factors. Chlorination takes place at temperatures lower than 2000 K, once the neutral fullereries are formed: Encapsulation is, however, mainly governed by the charge transfer, although the Sc center dot center dot center dot Sc distance is also playing a tole in the stability of Sc-2@C-66.
First author: Brovarets, OO, The significant role of the intermolecular CHMIDLINE HORIZONTALg ELLIPSISO/N hydrogen bonds in governing the biologically important pairsg of the DNA and RNA modified bases: a comprehensive theoreticalg investigation, JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS, 33, 1624, (2015)
Abstract: This paper is a logical continuation of the theoretical survey of the CHMIDLINE HORIZONTAL ELLIPSISO/N specific contacts in the nucleobase pairs using a wide arsenal of the modern methods, which was initiated in our previous study [J. Biomol. Struct. & Dynam., 2014, 32, 993-1022]. It was established that 34 CHMIDLINE HORIZONTAL ELLIPSISO and 7 CHMIDLINE HORIZONTAL ELLIPSISN interactions, that were detected by quantum-chemical calculations in the 39 biologically important pairs involving modified nucleobases, completely satisfy all geometrical, vibrational, electron-topological, in particular Bader's and "two-molecule" Koch and Popelier's, Grunenberg's compliance constants theory and natural bond orbital criteria indicating that they can be identified as true H-bonds. The geometrical criteria of the H-bond formation are fulfilled for all considered CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds without any exception. It was shown that the classical rule of the stretching vibration shifts does not work in the ~95% cases of the CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds. Furthermore, significant increase in the frequency of the out-of-plane deformation modes gamma(CH) under the formation of CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds and corresponding changes of their intensities can be also considered as reliable indicators of the H-bonding. We revealed high linear mutual correlations between the electron density, Laplacian of the electron density, H-bond energy at the (3, -1) bond critical points of the CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds, and different physico-chemical parameters of the CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds. We suggested that the electron density rho and the interaction energy E-(2) of the lone orbital pairs are the most reliable descriptors of the H-bonding. The linear dependence of the H-bond energy E-CHMIDLINE HORIZONTAL ELLIPSISO/N on the electron density rho was established: E-CHMIDLINE HORIZONTAL ELLIPSISO = 250.263 center dot rho – .380/258.255 center dot rho – .396 and E-CHMIDLINE HORIZONTAL ELLIPSISN = 196.800 center dot rho – .172/268.559 center dot rho – .703 obtained at the density functional theory (DFT)/Moller-Plesset (MP2) levels of theory, respectively. The studies of the interaction energies show that the contribution of the CHMIDLINE HORIZONTAL ELLIPSISO and CHMIDLINE HORIZONTAL ELLIPSISN H-bonds into the base pairs stability varies from 3.0/4.2 to 35.1/31.2% and from 3.0/4.3 to 44.4/46.5% at the DFT/MP2 levels of theory, accordingly. Energy decomposition analysis performed for all base pairs involving canonical and modified nucleobases defines the electrostatic attraction and Pauli repulsion as dominant stabilizing forces in all complexes. This observation was additionally confirmed by the results of the QTAIM delocalization indexes analysis. The studies reported here advance our understanding of the biological role of the weak CHMIDLINE HORIZONTAL ELLIPSISO/N H-bonds, that dictates the requirements for the structural and dynamical similarity of the canonical and mismatched pairs with Watson-Crick (WC) geometry, which facilitates their enzymatic incorporation into the DNA double helix during DNA replication. Thus, these H-bonds in the base pairs with WC geometry may be also considered as "the last drop" at the transmission of the electronic signal that launches the chemical incorporation of the incoming nucleoside triphosphate into DNA.
First author: Radunsky, C, Dioxygen Activation by an in situ Reduced Cu-II Hydrazone Complex, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 33, 4006, (2015)
Abstract: A Cu-II hydrazone complex has been synthesized that can be reduced in situ in boiling methanol to give the corresponding Cu-I complex. The latter complex readily activates dioxygen under ambient conditions, as was unambiguously shown by isotopic labeling studies. As a consequence of the dioxygen activation, the thienyl moiety appended to the hydrazone ligand is easily oxidized in position (C-HC-O), finally leading to a change in the coordination environment of the central metal ion. All relevant complexes have been structurally characterized by single-crystal X-ray diffraction analyses. The hydrazone ligand applied in this study does not mimic a biologically relevant coordination motif in copper-containing oxygenases. Nonetheless, the reactivity of the Cu-I complex resembles that found in many oxygenases, indicating that hydrazone ligands may be well-suited for the generation of novel bioinspired oxidation catalysts.
First author: Conradie, J, Mechanisms of Oxygen Atom Transfer between Main-Group Elements, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 33, 4138, (2015)
Abstract: Oxygen atom transfer (OAT) between main-group elements is pivotal to a number of industrial processes such as the synthesis of thionyl chloride (SO3 + SCl2SO2 + SOCl2) and sodium chlorate (3 NaOClNaClO3 + 2 NaCl), as well as the historic method of CO detection in mines via its reaction with I2O5 (I2O5 + 5 COI2 + 5 CO2). Surprisingly, little is known about the mechanisms of these and other OAT reactions involving main-group elements. Even the basic question as to whether such reactions are one-step, S(N)2-like displacements or multistep, involving oxo-bridged intermediates, remains largely unanswered. Extensive density functional theory calculations reported herein indicate a direct, S(N)2-like pathway as the norm for such processes.
First author: Christe, KO, Are DTTO and iso-DTTO Worthwhile Targets for Synthesis?, PROPELLANTS EXPLOSIVES PYROTECHNICS, 40, 463, (2015)
Abstract: Theoretical calculations were carried out for the isomeric di-1,2,3,4-tetrazine tetraoxides (DTTO and iso-DTTO). The most important explosion performance parameters, the detonation pressure and detonation velocity, are dominated by the densities and not by the heats of formation of these compounds. Since DTTO and iso-DTTO are unknown, reliable predictions of their crystal densities are crucial for an evaluation of the potential of these materials as explosives. In this study, the crystal densities were predicted using both Ammon's Atom/Functional Group and Atom Code Volume Additivity Parameters and Quantum Mechanical molecular Volume methods, resulting in similar densities and explosion parameters. Although the likely uncertainties in our predicted density values are difficult to assess due to a lack of experimental data for closely related known compounds, our results demonstrate that Shechter's originally proposed densities and performance parameters were grossly overestimated. Furthermore, it is shown that, based on our predicted density value ranges, DTTO and iso-DTTO could match or substantially outperform the best state of the art explosives, such as CL-20. Therefore, the synthesis of DTTO and iso-DTTO should be further pursued.
First author: Chiriki, S, Structural evolution of nucleobase clusters using force field models andg density functional theory, CHEMICAL PHYSICS LETTERS, 634, 166, (2015)
Abstract: We report global minima for all nucleobase clusters (nucleobase)(n), with 2 <= n <= 4. The global minima are predicted using force field based global optimization methods followed by local optimizations using the dispersion corrected DFT method. In this study, we use both non-polarizable (OPLS-AA) and polarizable (AMOEBA) force fields for global optimization. Here we emphasize on the reliability of AMOEBA force field used for predicting accurate global minima of nucleobase clusters. The average deviation in binding energies using AMOEBA is 3 kcal/mol from the DFT while the average deviation using OPLS-AA is 8 kcal/mol from DFT.
First author: Stevenson, JM, Solvation of nitrogen compounds in Titan's seas, precipitates, andg atmosphere, ICARUS, 256, 1, (2015)
Abstract: Saturn's moon Titan, dominated by its low, 90-95 K, surface temperature and methane seas, is shaped by physical and chemical processes unparalleled in any environment on Earth. Titan's upper atmosphere produces a rain of compounds such as acetonitrile, acrylonitrile, and acetylene, more familiar to chemical processing plants than to nature. The interaction of these compounds with Titan's seas is, to a large extent, unknown. As an important first step towards understanding these interactions, we investigate the solvation properties of many of these compounds in methane using multiple theoretical approaches, including cubic equations of state, Statistical Associating Fluid Theory, the Conductor like Screening Model for Real Solvents, and all-atom Molecular Dynamics.
First author: Stasyuk, OA, Theoretical study of electron-attracting ability of the nitro group:g classical and reverse substituent effects, STRUCTURAL CHEMISTRY, 26, 905, (2015)
Abstract: This study presents a quantum chemistry modeling of the substituent effect. For this purpose, a uniform approach-the model termed as "charge of substituent active region" (cSAR, defined as a sum of atomic charges at the substituent and the ipso carbon atom)-has been used. Its reliability has been confirmed by a quantitative description of the electron-attracting ability of the nitro group, and finally, the reverse substituent effect, showing the influence of reaction site (Y) on the properties of substituent (X), has been introduced and documented. The cSAR model has been applied to para-substituted nitrobenzene derivatives in which the nitro group acts either as a reaction site (classical substituent effect, with X = NO2, CN, CHO, COOMe, COMe, CF3, Cl, H, Me, OMe, NH2 and NHMe) or as a substituent (reverse substituent effect, with Y = NH-, NH2, H and NH3+). Calculation was performed using BLYP functional with DFT-D3 correction and TZ2P basis set. Application of different assessments of atomic charges (Voronoi, Hirshfeld, Bader, Weinhold and Mulliken) leads to good correlation between calculated cSAR values.
First author: Baranac-Stojanovic, M, Theoretical analysis of the rotational barrier in ethane: cause andg consequences, STRUCTURAL CHEMISTRY, 26, 989, (2015)
Abstract: On the basis of energy decomposition analysis, the rotational energy profile of ethane is explained by using two models: rigid rotation with instantaneous geometry relaxations of the eclipsed and staggered conformations and relaxed rotation with continuous geometry relaxations. Both models can be applied to the real system. A distinction between the cause of an initial energy rise and energetic consequences of structural changes accompanying the rotation is made. It is concluded that the increased Pauli repulsion is the main cause for the initial energy rise and geometry changes. However, after the structural changes take place, the Pauli repulsion is not responsible for the higher energy of the eclipsed state. It then originates from energetic consequences of geometry changes, which include decrease in electrostatic and orbital stabilization energies, mainly due to the C-C bond lengthening, and an energy rise due tomethyl groups bending.
First author: Chen, L, Strong Core@Shell Dependence in Surface-Enhanced Raman Scattering ofg Pyridine on Stable 13-Atom Silver-Caged Bimetallic Clusters, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 17429, (2015)
Abstract: On the basis of calculations using time-dependent density functional theory, we conducted detailed analyses of the surface-enhanced Raman scattering (SERS) of pyridine adsorbed on 13-atom icosahedral M@Auiz and M@Ag-12 (M = Mo, W) clusters in this article. Surprisingly, we find that, although the SERS enhancements for all complexes can reach the order of 104, the signals of pyridine on M@Ag-12 at charge transfer (CT) transition excitations are twice as much as that of pyridine on M@Au-12, and the corresponding energies used for SERS excitations are significantly different in the low-energy region of 1.63-2.10 eV. The interactive modulation between the core and shell can produce varying strong CT transitions from metal clusters to pyridine, which tunes the SERS enhancements with altered optical properties. The complexes of pyridine on silver-caged clusters are more easily influenced by the tunability of the core than that of pyridine on gold-caged clusters. Our analyses are expected to provide a theoretical basis for experimentally synthesizing multicomponent SERS substrates and exploring the dependence of SERS enhancement on the synergies between the different components in core@shell binary metal clusters.
First author: Frisenda, R, Single-Molecule Break Junctions Based on a Perylene-Diimideg Cyano-Functionalized (PDI8-CN2) Derivative, NANOSCALE RESEARCH LETTERS, 10, 17429, (2015)
Abstract: In this letter, we report the single-molecule conductance properties of a cyano-functionalized perylene-diimide derivative (PDI8-CN2) investigated with gold nano-electrodes. This molecule is of large interest for the fabrication of high-performance and air-stable n-type organic field-effect transistors. Low-bias experiments performed on mechanically controllable break junctions reveal the presence of two different values of the single-molecule conductance, which differ by about two orders of magnitudes. Up to date, this feature was never observed for other perylene-diimide compounds having alternative chemical moieties attached to the basic aromatic core. Theoretical calculations suggest that the highest single-molecule conductance value here observed, comprised between 10(-2) and 10(-3) G(0), is related to a charge transport path directly linking the two cyano groups.
First author: Yang, T, Sc2O@T-d(19151)-C-76: Hindered Cluster Motion inside a Tetrahedralg Carbon Cage Probed by Crystallographic and Computational Studies, CHEMISTRY-A EUROPEAN JOURNAL, 21, 11110, (2015)
Abstract: A new cluster fullerene, Sc2O@T-d(19151)-C-76, has been isolated and characterized by mass spectrometry, UV/Vis/NIR absorption, Sc-45 NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously assigned the cage structure as T-d(19151)-C-76, which is the first tetrahedral fullerene cage characterized by single-crystal X-ray diffraction. This study also demonstrated that the Sc2O cluster has a much smaller Sc-O-Sc angle than that of Sc2O@C-s(6)-C-82 and the Sc2O unit is fully ordered inside the T-d(19151)-C-76 cage. Computational studies further revealed that the cluster motion of the Sc2O is more restrained in the T-d(19151)-C-76 cage than that in the C-s(6)-C-82 cage. These results suggest that cage size affects not only the shapes but also the cluster motion inside fullerene cages.
First author: Dresselhaus, T, Part and whole in wavefunction/DFT embedding, THEORETICAL CHEMISTRY ACCOUNTS, 134, 11110, (2015)
Abstract: Density functional theory (DFT)-based subsystem and embedding methods have found a widespread use in Quantum Chemistry. The combination of correlated wavefunction (WF) methods and density-based embedding methods is particularly promising for accurate descriptions of complex systems. Here, we address some conceptual issues in such WF/DFT methods concerning (1) the interpretation of wavefunctions and densities in these frameworks, (2) the interpretation of subsystem and supersystem density changes as a polarization of the electronic system, and (3) non-orthogonality effects between wavefunctions of ground and excited states in WF/DFT embedding making use of state-specific embedding potentials. Illustrative examples are provided to analyze the significance of these issues in practical calculations. We find that physically reasonable subsystem densities and subsystem dipole moments can often be obtained from subsystem calculations making use of typical setups in practice, in spite of formal issues that are in principle in conflict with such interpretations. For excited-state WF/DFT calculations, we demonstrate that orthogonality violations due to state-specific embedding potentials are usually small.
First author: Lu, JS, Solid-State O-17 NMR of Oxygen-Nitrogen Singly Bonded Compounds:g Hydroxylammonium Chloride and Sodium Trioxodinitrate (Angeli's Salt), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 8133, (2015)
Abstract: We report a solid-state NMR study of O-17-labeled hydroxylammonium chloride ([(HO)-O-17-NH3]Cl) and sodium trioxodinitrate monohydrate (Na-2[(ONNO2)-O-17]center dot H2O, Angelis salt). The common feature in these two compounds is that they both contain oxygen atoms that are singly bonded to nitrogen. For this class of oxygen-containing functional groups, there is very limited solid-state O-17 NMR data in the literature. In this work, we experimentally measured the O-17 chemical shift and quadrupolar coupling tensors. With the aid of plane-wave DFT computation, the O-17 NMR tensor orientations were determined in the molecular frame of reference. We found that the characteristic feature of an ON single bond is that the O-17 nucleus exhibits a large quadrupolar coupling constant (13-15 MHz) but a rather small chemical shift anisotropy (100-250 ppm), in sharp contrast with the nitroso (O=N) functional group for which both quantities are very large (e.g., 16 MHz and 3000 ppm, respectively).
First author: Karimova, NV, Time-Dependent Density Functional Theory Investigation of the Electronicg Structure and Chiroptical Properties of Curved and Helical Silverg Nanowires, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 8163, (2015)
Abstract: Time-dependent density functional theory methods are employed to examine the evolution of the absorption and circular dichroism (CD) spectra of neutral bare silver helical nanostructures as a function of their geometrical parameters. Calculations of excited states to determine optical absorption and CD spectra were performed using the SAOP/TZP level of theory. In our model, the geometry of the helical silver chain is dependent on the Ag-Ag-Ag bond angle and the Ag-Ag-Ag-Ag dihedral angle. The influence of different geometrical structures on the optical absorption and CD spectra were studied for helical and planar Ag-8. Silver nanowires Ag-n (n = 4, 6, 8, 10, 12) were examined to determine the effect of the helical chain length on the electronic properties. The results show that when the metal atomic chain loses planarity, strong CD signals arise; the intensities of the CD peaks for these structures are strongly affected by the shape and length of the silver nanowires. The theoretically predicted CD spectra of the nonplanar Ag-4 and Ag-6 model systems show good agreement in spectral shapes and reasonable agreement in peak locations compared to experimental data for silver-DNA clusters. However, the theoretical and experimental results for the longer Ag-12 wire show larger differences in the peak locations, which could potentially be caused by effects such as the presence of DNA and cationic silver atoms in the experimental system.
First author: Wachtler, E, Metallophilic Contacts in 2-C6F4PPh2 Bridged Heterobinuclear Complexes:g A Crystallographic and Computational Study, INORGANIC CHEMISTRY, 54, 6947, (2015)
Abstract: Treatment of the bis(chelate) complex trans-[Pd(kappa(2)-2-C6F4PPh2)(2)] (7) with PMe3 gave trans-[Pd(kappa C-2-C6F4PPh2)(2)(PMe3)(2)] (13) as a mixture of syn- and anti-isomers. Reaction of 13 with CuCl, AgCl, or [AuCl(tht)] (tht = tetrahydrothiophene) gave the heterobinuclear complexes [(Me3P)(2)Pd(mu-2-C6F4PPh2)(2)MCl] [M = Cu (14), Ag (15), Au (16)] from which the corresponding salts [(Me3P)(2)Pd(mu-2-C6F4PPh2)(2)M]PF6 [M = Cu (17), Ag (18), Au (19)] could be prepared by abstraction of the chloro ligand with TlPF6; 18, as well as its triflato (20) and trifluoroacetato (21) analogues, were also prepared directly from 13 and the appropriate silver salt. Reaction of 13 with [AuCl(PMe3)] gave the zwitterionic complex [(Me3P)PdCl(mu-2-C6F4PPh2)(2)Au] (24) in which the 2-C6F4PPh2 ligands are in a head-to-head arrangement. In contrast, the analogous reaction with [AuCl(PPh3)] gave [(Ph3P)PdCl(mu-2-C6F4PPh2)(2)Au] (25) with a head-to-tail ligand arrangement. Single crystal X-ray diffraction studies of complexes 14-21 show short metal metal separations [2.7707(11)-2.9423(3) angstrom] suggestive of attractive noncovalent (dispersion) interactions, a conclusion that is supported by theoretical calculations of the electron localization function and the noncovalent interactions descriptor.
First author: Park, YC, On the relation between adiabatic time dependent density functionalg theory (TDDFT) and the Delta SCF-DFT method. Introducing a numericallyg stable Delta SCF-DFT scheme for local functionals based on constrictedg variational DFT, MOLECULAR PHYSICS, 113, 1636, (2015)
Abstract: In Delta SCF density functional theory studies of a i -> a transition one performs separate fully self-consistent field calculations on the ground state configuration (i)(n) (n = 1,2) and the excited state configuration (i)(n – 1)a. The excitation energy for the transition i -> a is subsequently determined as the Kohn-Sham energy difference Delta E-i -> a = E[i(n – 1)a] – E[i(n)] between the ground state (i)(n) and the excited state configuration (i)(n – 1)a. The Delta SCF scheme has been applied extensively and works well for lower energy excitations provided that they can be represented by a single orbital replacement or transition i -> a. However, for excitations of higher energy Delta SCF tends to become numerically unstable with a variational collapse to transitions of lower energy. We demonstrate here a numerically stable Delta SCF scheme for local functionals that is guaranteed not to collapse on excited configurations of lower energy as well as the ground state. The new scheme is based on constricted variational density functional theory in which the canonical ground state orbitals are allowed to relax (R-CV(infinity)-DFT). Since it is restricted to a single orbital replacement i -> a it is termed SOR-R-CV(infinity)-DFT.
First author: Cimpoesu, F, On exchange coupling and bonding in the Gd-2@C-80 and Gd-2@C79Ng endohedral dimetallo-fullerenes, MOLECULAR PHYSICS, 113, 1712, (2015)
Abstract: A series of computational experiments performed with various methods belonging to wave-function and density functional theories approaches the issue of bonding regime and exchange coupling in the title compounds. Gd-2@C-80 is computed with a very weak exchange coupling, the sign depending on the method, while Gd-2@C79N has resulted with a strong coupling and ferromagnetic ground state, irrespective of the computational approach. The multi-configuration calculation and broken symmetry estimation are yielding closely coincident coupling constants, of about J similar to 400 cm(-1). No experimental estimation exists, but the ferromagnetic ground state of Gd-2@C79N is confirmed from paramagnetic resonance data. The different behaviour is due to particularities of electron accommodation in the orbital scheme. The exchange effects localised on atom lead to preference for parallel alignment of the electrons placed in the 4f and 5d lanthanide shells, determining also a ferromagnetic inter-centre coupling. The structural insight is completed with a ligand field analysis of the density functional theory results in the context of frozen density embedding. The energy decomposition analysis of bonding effects is also discussed. Finally, with the help of home-made codes (named Xatom+Xsphere), a model for the atom encapsulated in a cage is designed, the exemplified numeric experiments showing relevance for the considered endohedral metallo-fullerene issues.
First author: Frisenda, R, Electrical properties and mechanical stability of anchoring groups forg single-molecule electronics, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 1558, (2015)
Abstract: We report on an experimental investigation of transport through single molecules, trapped between two gold nano-electrodes fabricated with the mechanically controlled break junction (MCBJ) technique. The four molecules studied share the same core structure, namely oligo(phenylene ethynylene) (OPE3), while having different aurophilic anchoring groups: thiol (SAc), methyl sulfide (SMe), pyridyl (Py) and amine (NH2). The focus of this paper is on the combined characterization of the electrical and mechanical properties determined by the anchoring groups. From conductance histograms we find that thiol anchored molecules provide the highest conductance; a single-level model fit to current-voltage characteristics suggests that SAc groups exhibit a higher electronic coupling to the electrodes, together with better level alignment than the other three groups. An analysis of the mechanical stability, recording the lifetime in a self-breaking method, shows that Py and SAc yield the most stable junctions while SMe form short-lived junctions. Density functional theory combined with non-equlibrium Green's function calculations help in elucidating the experimental findings.
First author: Ding, WJ, Performance of Twelve Density Functional Theory Methods in theg Characterization of Three Trivalent Uranium Complexes, ACTA PHYSICO-CHIMICA SINICA, 31, 1283, (2015)
Abstract: We report a comparative study on the characterization of three trivalent uranium complexes using 12 density functional theory (DFT) methods, i.e., BP86, PBE, B3LYP, B3PW91, BHandHLYP, PBE0, X3LYP, CAM-B3LYP, TPSS, M06L, M06, and M06-2X, representing (meta-)GGA and hybrid (meta-)GGA levels of treatment of molecular systems. The MP2 method was used in single-point calculations to provide an ab initio view of the electronic structure. Three model systems in the experimental work on the activation of CO2 and CS2 by a trivalent uranium complex (Tp*)(2)U-eta(1)-CH2Ph (Cpd2) were used i.e., (Tp*)(2)U-eta(1)-CH2Ph (Cpd2), (Tp*)(2)U-kappa(2)-O2CCH2Ph (Cpd3), and (Tp*)(2)U-kappa(2)-S2CCH2Ph (Cpd4) (Tp=hydrotris(3,5-dimethylpyrazolyl)borate). The hybrid functionals, B3LYP and B3PW91, displayed good performance in view of both the geometrical and electronic structures. The MP2 method generated consistent results as OFT methods for Cpd2 and Cpd3, while provided an odd picture of the electronic structure of Cpd4 that may be due to its single determinant feature, leading to its capture of an electronic configuration of Cpd4 different from the one with the DFT methods. The use of a quasi-relativistic 5f-in-core ECP (LPP) treatment for U(III) in the thermodynamic calculations was supported by the calculations with a small-core ECP treatment (SPP) for U. Owing to increasing interests in low-valent actinide molecular systems, this work complements previous comparative studies, which mainly focus on high-valent actinide complexes, and provides timely information on the performance of 12 widely used DFT methods in studying low-valent actinide systems. It is expected to contribute to a more sensible selection of DFT methods in the study of low-valent actinide molecular systems.
First author: Zhao, YX, Understanding the Effect of Monomeric Iridium(III/IV) Aquo Complexes ong the Photoelectrochemistry of IrOx center dot nH(2)O-Catalyzedg Water-Splitting Systems, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 8749, (2015)
Abstract: Soluble, monomeric Ir(III/IV) complexes strongly affect the photoelectrochemical performance of IrOx.nH(2)O-catalyzed photoanodes for the oxygen evolution reaction (OER). The synthesis of IrOx.nH(2)O colloids by alkaline hydrolysis of Ir(III) or Ir(IV) salts proceeds through monomeric intermediates that were characterized using electrochemical and spectroscopic methods and modeled in TDDFT calculations. In air-saturated solutions, the monomers exist in a mixture of Ir(III) and Ir(IV) oxidation states, where the most likely formulations at pH 13 are [Ir(OH)(5)(H2O)](2) and [Ir(OH)(6)](2-), respectively. These monomeric anions strongly adsorb onto IrOx.nH(2)O colloids but can be removed by precipitation of the colloids with isopropanol. The monomeric anions strongly adsorb onto TiO2, and they promote the adsorption of ligand-free IrOx.nH(2)O colloids onto mesoporous titania photoanodes. However, the reversible adsorption/desorption of electroactive monomers effectively short-circuits the photoanode redox cycle and thus dramatically degrades the photoelectrochemical performance of the cell. The growth of a dense TiO2 barrier layer prevents access of soluble monomeric anions to the interface between the oxide semiconductor and the electrode back contact (a fluorinated tin oxide transparent conductor) and leads to improved photoanode performance. Purified IrOx.nH(2)O colloids, which contain no adsorbed monomer, give improved performance at the same electrodes. These results explain earlier observations that IrOx.nH(2)O catalysts can dramatically degrade the performance of metal oxide photoanodes for the OER reaction.
First author: Rampino, S, Gold-superheavy-element interaction in diatomics and cluster adducts: Ag combined four-component Dirac-Kohn-Sham/charge-displacement study, JOURNAL OF CHEMICAL PHYSICS, 143, 8749, (2015)
Abstract: The chemistry of superheavy elements (Z >= 104) is actively investigated in atom-at-a-time experiments of volatility through adsorption on gold surfaces. In this context, common guidelines for interpretation based on group trends in the periodic table should be used cautiously, because relativistic effects play a central role and may cause predictions to fall short. In this paper, we present an all-electron four-component Dirac-Kohn-Sham comparative study of the interaction of gold with Cn (Z = 112), Fl (Z = 114), and Uuo (Z = 118) versus their lighter homologues of the 6th period, Hg, Pb, and Rn plus the noble gas Xe. Calculations were carried out for Au-E (E = Hg, Cn, Pb, Fl, Xe, Rn, Uuo), Au-7- and Au-20-E (E = Hg, Cn, Pb, Fl, Rn) complexes, where Au-7 (planar) and Au-20 (pyramidal) are experimentally determined clusters having structures of increasing complexity. Results are analysed both in terms of the energetics of the complexes and of the electron charge rearrangement accompanying their formation. In line with the available experimental data, Cn and more markedly Fl are found to be less reactive than their lighter homologues. On the contrary, Uuo is found to be more reactive than Rn and Xe. Cn forms the weakest bond with the gold atom, compared to Fl and Uuo. The reactivity of Fl decreases with increasing gold-fragment size more rapidly than that of Cn and, as a consequence, the order of the reactivity of these two elements is inverted upon reaching the Au-20-cluster adduct. Density difference maps between adducts and fragments reveal similarities in the behaviour of Cn and Xe, and in that of Uuo and the more reactive species Hg and Pb. These findings are given a quantitative ground via charge-displacement analysis.
First author: van Weerdenburg, BJA, Computational (DFT) and Experimental (EXAFS) Study of the Interaction ofg [Ir(IMes)(H)(2)(L)(3)] with Substrates and Co-substrates Relevant forg SABRE in Dilute Systems, CHEMISTRY-A EUROPEAN JOURNAL, 21, 10482, (2015)
Abstract: Signal amplification by reversible exchange (SABRE) is an emerging hyperpolarization method in NMR spectroscopy, in which hyperpolarization is transferred through the scalar coupling network of para-hydrogen derived hydrides in a metal complex to a reversibly bound substrate. Substrates can even be hyperpolarized at concentrations below that of the metal complex by addition of a suitable co-substrate. Here we investigate the catalytic system used for trace detection in NMR spectroscopy with [Ir(IMes)(H)(2)(L)(3)](+) (IMes=1,3-dimesitylimidazol-2-ylidene) as catalyst, pyridine as a substrate and 1-methyl-1,2,3-triazole as co-substrate in great detail. With density functional theory (DFT), validated by extended X-ray absorption fine structure (EXAFS) experiments, we provide explanations for the relative abundance of the observed metal complexes, as well as their contribution to SABRE. We have established that the interaction between iridium and ligands cis to IMes is weaker than that with the trans ligand, and that in mixed complexes with pyridine and triazole, the latter preferentially takes up the trans position.
First author: Faucher, A, Spin-Spin Coupling between Quadrupolar Nuclei in Solids: B-11-As-75 Sping Pairs in Lewis Acid-Base Adducts, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 6949, (2015)
Abstract: Solid-state B-11 NMR measurements of Lewis acid base adducts of the form R3AsBR3′ (R = Me, Et, Ph; R' = H, Ph, C6F5) were carried out at several magnetic field strengths (e.g., B-0 = 21.14, 11.75, and 7.05 T). The B-11 NMR spectra of these adducts exhibit residual dipolar coupling under MAS conditions, allowing for the determination of effective dipolar coupling constants, R-eff(As-75, B-11) as well as the sign of the As-75 nuclear quadrupolar coupling constants. Values of R-eff(As-75, B-11) range from 500 to 700 Hz. Small isotropic I-couplings are resolved in some cases, and the sign of (1)J(As-75, B-11) is determined. Values of C-Q(As-75) measured at B-0 = 21.14 T for these triarylborane Lewis acid base adducts range from -82 ± 2 MHz for Et3AsB(C6F5)(3) to -146 ± 1 MHz for Ph3AsBPh3. For Ph3AsBH3, two crystallographically nonequivalent sites are identified with C-Q(As-75) values of -153 and -151 ± 1 MHz. For the uncoordinated Lewis base, Ph3As, four As-75 sites with C-Q(As-75) values ranging from 193.5 to -194.4 ± 2 MHz are identified. At these applied magnetic field strengths, the As-75 quadrupolar interaction does not satisfy high-field approximation criteria, and thus, an exact treatment was used to describe this interaction in B-11 and As-75 NMR spectral simulations. NMR parameters calculated using the ADF and CASTEP program packages support the experimentally derived parameters in both magnitude and sign. These experiments add to the limited body of literature on solid-state As-75 NMR spectroscopy and serve as examples of spin spin-coupled quadrupolar spin pairs, which are also rarely treated in the literature.
First author: Blachly, PG, Broken-Symmetry DFT Computations for the Reaction Pathway of IspH, ang Iron-Sulfur Enzyme in Pathogenic Bacteria, INORGANIC CHEMISTRY, 54, 6439, (2015)
Abstract: The recently discovered methylerythritol phosphate (MEP) pathway provides new targets for the development of antibacterial and antimalarial drugs. In the final step of the MEP pathway, the [4Fe-4S] IspH protein catalyzes the 2e(-)/2H(+) reductive dehydroxylation of (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) to afford the isoprenoid precursors isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Recent experiments have attempted to elucidate the IspH catalytic mechanism to drive inhibitor development. Two competing mechanisms have recently emerged, differentiated by their proposed HMBPP binding modes upon 1e(-) reduction of the [4Fe-4S] cluster: (1) a Birch reduction mechanism, in which HMBPP remains bound to the [4Fe-4S] cluster through its terminal C-4-OH group (ROH-bound) until the OH is cleaved as water; and (2) an organometallic mechanism, in which the C-4-OH group rotates away from the [4Fe-4S] cluster, allowing the HMBPP olefin group to form a metallacycle complex with the apical iron (eta(2)-bound). We perform broken-symmetry density functional theory computations to assess the energies and reduction potentials associated with the ROH- and eta(2)-bound states implicated by these competing mechanisms. Reduction potentials obtained for ROH-bound states are more negative (-1.4 to 1.0 V) than what is typically expected of [4Fe-4S] ferredoxin proteins. Instead, we find that eta(2)-bound states are lower in energy than ROH-bound states when the [4Fe-4S] cluster is 1e(-) reduced. Furthermore, eta(2)-bound states can already be generated in the oxidized state, yielding reduction potentials of ca. -700 mV when electron addition occurs after rotation of the HMBPP C-4-OH group. We demonstrate that such eta(2)-bound states are kinetically accessible both when the IspH [4Fe-4S] cluster is oxidized and 1e(-) reduced. The energetically preferred pathway gives 1e(-) reduction of the cluster after substrate conformational change, generating the 1e(-) reduced intermediate proposed in the organometallic mechanism.
First author: Matsumoto, A, Tetrabenzoperipentacene: Stable Five-Electron Donating Ability and ag Discrete Triple-Layered -Graphite Form in the Solid State, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 8175, (2015)
Abstract: An oxidative ring-closure reaction of a tetranaphthylpyrene derivative led to the synthesis of a 56 all-carbon conjugated tetrabenzoperipentacene. In the single-crystal X-ray structure, three molecules make a triple-layered cluster by -stacking, wherein each layer rotates by 120 degrees, and is thus considered a petit -graphite. As for the optical properties, the Stokes shift is extremely small (10cm(-1)), thus indicating its remarkably rigid framework. The tetrabenzoperipentacene exhibits reversible five-electron oxidation waves in cyclic voltammetry, and is regarded as a counterpart to the fullerene C-60 in terms of stable multicharge-storage nanocarbon materials.
First author: Rogachev, AY, Molecular CsF5 and CsF2+, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 8275, (2015)
Abstract: D-5h star-like CsF5, formally isoelectronic with known XeF5- ion, is computed to be a local minimum on the potential energy surface of CsF5, surrounded by reasonably large activation energies for its exothermic decomposition to CsF+2F(2), or to CsF3(three isomeric forms)+F-2, or for rearrangement to a significantly more stable isomer, a classical Cs+ complex of F-5(-). Similarly the CsF2+ ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs.
First author: Wang, B, Correlation between electron delocalization and structural planarizationg in small water rings, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 115, 817, (2015)
Abstract: The discovery of the covalent-like character of the hydrogen bonding (H-bonding) system [Science342, 611(2013)] has promoted a renewal of our understanding of the electronic and geometric structures of water clusters. In this work, based on density functional theory calculations, we show that the preferential formation of a stable quasiplanar structure of (H2O)(n)(n=3-6) is closely related to three kinds of delocalized molecular orbitals (MOs; denoted as MO-I, II, and III) of water rings. These originate from the 2p lone pair electrons of oxygen (O), the 2p bond electrons of O and the 1s electrons of H and the 2s electrons of O and 1s electrons of H, respectively. To maximize the orbital overlaps of the three MOs, geometric planarization is needed. The contribution of the orbital interaction is more than 30% in all the water rings according to our energy decomposition analysis, highlighting the considerable covalent-like characters of H-bonds.
First author: Yildirim, MH, Synthesis, structural and computational characterization ofg 2-amino-3,5-diiodobenzoic acid and 2-amino-3,5-dibromobenzoic acid, SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 146, 50, (2015)
Abstract: The benzoic acid compounds 2-amino-3,5-dibromobenzoic acid (2A35Br) and 2-amino-3,5-diiodobenzoic (2A35I) acid have been synthesized and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, UV-Vis spectroscopy and computational methods. Molecular geometry, intra- and inter-molecular interactions have been investigated by using X-ray diffraction technique. Fundamental vibrational bands of the title compounds were founded by FT-IR and UV-Vis method was used to obtain electronic bands. Geometry optimizations and the calculation of IR frequencies were performed both Gaussian type orbitals at Gaussian 09W and Slater type orbitals at ADF2009.01 software. The calculations are compatible with the experiment results. In addition, geometrical parameters, energies, HOMO-LUMO gaps and electrophilicity indexes have been calculated for thirty possible positional isomers of 2A35Br and 2A35I. Calculations show that 2A35Br and 2A35I isomers have the lowest energy, the narrowest HOMO-LUMO gap and the highest electrophilicity index values. Molecular electrostatic potential maps, Fukui indices, natural bond orbital analysis, thermodynamic parameters and non-linear optical properties of the 2A35Br and 2A35I were also investigated by theoretical calculations.
First author: Nasiri, R, The effects of internal molecular dynamics on theg evaporation/condensation of n-dodecane, THEORETICAL CHEMISTRY ACCOUNTS, 134, 50, (2015)
Abstract: The effects of conformerisation and internal molecular dynamics of n-dodecane conformers on energy transfers between gas and liquid phases are investigated. Bond energies, Gibbs free energies of internal dynamics of a set of n-dodecane conformers, and energies of the molecules colliding with the surface of an n-dodecane nanodroplet are studied using quantum chemical calculations (DFT with omega B97X-D/cc-pVTZ and semi-empirical PM7) and ReaxFF method. The results of the analysis show that the accuracy of the methods increases as we move from the application of PM7 to the application of ReaxFF and then to DFT. Different temperature dependencies of internal Gibbs free energies of conformers in the gas and liquid phases are expected to affect the heat and mass transfer processes between them. The calculations for the gas and liquid (using the quantum solvation model; SMD) phases show significant differences in the internal dynamics of conformers and demonstrate an entropy-enthalpy competition in the evaporation/condensation of an ensemble of the conformers.
First author: Alvarado-Soto, L, A Theoretical Study of the Binding of [Re6Se8(OH)(2)(H2O)(4)] Rheniumg Clusters to DNA Purine Base Guanine, MATERIALS, 8, 3938, (2015)
Abstract: Hexanuclear rhenium complexes are promising candidates for use as antitumor drugs. However, to date, there has been no investigation into the nature of their binding to DNA. In this study, density functional theory (DFT) was used to examine the binding of [Re6Se8(OH)(2)(H2O)(4)] to the DNA purine base guanine. The geometrical structures of cluster-guanine adducts in water were modeled at the zero order regular approximation (ZORA)-PW91 level. Calculating the bond energies allowed us to compare the cis and trans forms of the cluster, and a possible manners of interaction between [Re6Se8(OH)(2)(H2O)(3)] clusters and DNA was obtained and explained.
First author: Dicks, JP, Synthesis, Structure and Redox Properties of Asymmetricg (Cyclopentadienyl)(ene-1,2-dithiolate)cobalt(III) Complexes Containingg Phenyl, Pyridyl and Pyrazinyl Units, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 8, 3550, (2015)
Abstract: The compounds [(eta(5)-C5H5)Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized and characterized by elemental analysis, H-1 NMR, mass spectrometry and X-ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH2Cl2 solution each compound undergoes a reversible one-electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5: 1 excess of trifluoroacetic acid the one-electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [1](y), [2](y) and [3](y) (y = 0 or -1) and the monoprotonated forms [2H](z) and [3H](z) (z = +1 or 0), and this has provided insight into the nature of the redox-active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene-1,2-dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring-opened form of the molybdenum cofactor of oxygen-atom-transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle.
First author: Chulhai, DV, Frozen Density Embedding with External Orthogonality in De localizedg Covalent Systems, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 3080, (2015)
Abstract: Frozen density embedding (FDE) has become a popular subsystem density functional theory (DFT) method for systems with weakly overlapping Charge densities. The failure of this method for strongly interacting and covalent systems is due to the approximate kinetic energy density functional (KEDF), although the need for approximate KEDFs may be eliminated if each subsystem's Kohn Sham (KS) orbitals are orthogonal to the other, termed external orthogonality (EO). We present an implementation of EO into the FDE framework within the Amsterdam denSity fiinctionaI program package, using the level-shift projection Ioperator method. We generalize this method to remove the need for orbital localization schemes and to include multiple subsystems, and we show that the exact KS-DFT energies and densities may be reproduced through, iterative freeze-and-thaw cycles for a number of systems, including a charge delocalized benzene molecule starting from atomic subsystems. Finally, we examine the possibility of a truncated basis for systems with and without charge delocalization, and found that subsystems require a basis that allows them to correctly describe the supermolecular delocalized orbitals.
First author: Hu, JZ, Investigation of the Structure and Active Sites of TiO2 Nanorodg Supported VOx Catalysts by High-Field and Fast-Spinning V-51 MAS NMR, ACS CATALYSIS, 5, 3945, (2015)
Abstract: Supported VOx/TiO2-rod catalysts were studied by V-51 MAS NMR at high field using a sample spinning rate of 55 kHz. The superior spectral resolution allows for the observation of at least five vanadate species. The assignment of these vanadate species was carried out by quantum chemical calculations of V-51 NMR chemical shifts of model V surface structures. Methanol oxidative dehydrogenation (ODH) was used to establish a correlation between catalytic activity and the various surface V sites. It is found that monomeric V species are predominant at low vanadium loadings with two V-51 NMR peaks observed at about -502 and -529 ppm. V dimers with two bridged oxygens result in a peak at about -555 ppm. Vanadate dimers and polyvanadates connected by one bridged oxygen atom between two adjacent V atoms resonate at about -630 ppm. A positive correlation is found between the V dimers, giving rise to the -555 ppm peak, and the ODH rate, and an even better correlation is obtained by including V monomer contributions. This result suggests that surface V dimers related to the -555 ppm peak and monomers are the primary active sites for the methanol ODH reaction. Furthermore, a portion of the V species is found to be invisible to NMR and the level of such invisibility increases with decreasing V loading levels, suggesting the existence of paramagnetic V species at the surface. These paramagnetic V species are also found to be much less active in methanol ODH.
First author: Ciborska, A, The Syntheses and Crystal Structures of the First Disiloxane-1,3-dithiolg and Its Cadmium Complex, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 5, 3059, (2015)
Abstract: The silicon-sulfur compound bis-1,3-[di(2,6-diisopropylphenoxy)]disiloxane-1,3-dithiol was obtained from silicon disulfide and 2,6-diisopropylphenol in a reaction catalyzed by imidazole or 4-(dimethylamino)pyridine (DMAP). The disiloxane-1,3-dithiol is produced in a low yield but in a repeatable manner and can be isolated as colorless crystals. The X-ray crystal structure of the compound reveals a linear or close-to-linear Si-O-Si angle and a mutual trans position of the two hydrosulfido groups. The compound forms a chelating mononuclear complex with cadmium ions. In the complex, the sulfido groups adopt a cis conformation, and the Si-O-Siangle deviates from linearity. The molecular structure of the compound is discussed on the basis of DFT calculations.
First author: Wolters, LP, The activation strain model and molecular orbital theory, WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE, 5, 324, (2015)
Abstract: The activation strain model is a powerful tool for understanding reactivity, or inertness, of molecular species. This is done by relating the relative energy of a molecular complex along the reaction energy profile to the structural rigidity of the reactants and the strength of their mutual interactions: Delta E(zeta) = Delta E-strain(zeta) + Delta E-int(zeta). We provide a detailed discussion of the model, and elaborate on its strong connection with molecular orbital theory. Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms. This methodology may reveal intriguing parallels between completely different types of chemical transformations. Thus, the activation strain model constitutes a unifying framework that furthers the development of cross-disciplinary concepts throughout various fields of chemistry. We illustrate the activation strain model in action with selected examples from literature. These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process.
First author: Powell, BJ, Theories of phosphorescence in organo-transition metal complexes – Fromg relativistic effects to simple models and design principles for organicg light-emitting diodes, COORDINATION CHEMISTRY REVIEWS, 295, 46, (2015)
Abstract: We review theories of phosphorescence in cyclometalated complexes. We focus primarily on pseudooctahedrally coordinated t(2g)(6). metals (e.g., [Os(II)(bpy)(3)](2+), Ir(III)(ppy)(3) and Ir(III)(ptz)(3)) as, for reasons that are explored in detail, these show particularly strong phosphorescence. We discuss both first principles approaches and semi-empirical models, e.g., ligand field theory. We show that together these provide a clear understanding of the photophysics and in particular the lowest energy triplet excitation, T-1. In order to build a good model relativistic effects need to be included. The role of spin-orbit coupling is well-known, but scalar relativistic effects are also large – and are therefore also introduced and discussed. No expertise in special relativity or relativistic quantum mechanics is assumed and a pedagogical introduction to these subjects is given. Once both scalar relativistic effects and spin-orbit coupling are included, time dependent density functional theory (TDDFF) provides quantitatively accurate predictions of the radiative decay rates of the substates of T-1 in phosphorescent organotransition-metal complexes. We describe the pseudo-angular momentum model, and show that it reproduces the key experimental findings. For example, this model provides a simple explanation of the relative radiative rates of the substates of T-1, which differ by orders of magnitude. Special emphasis is placed on materials with potential applications as active materials in organic light-emitting diodes (OLEDs) and principles for the design of new complexes are identified on the basis of the insights provided by the theories reviewed. We discuss the remaining theoretical challenges, which include deepening our understanding of solvent effects and, vitally, understanding and predicting non-radiative decay rates.
First author: Mehmood, U, Theoretical study of benzene/thiophene based photosensitizers for dyeg sensitized solar cells (DSSCs), DYES AND PIGMENTS, 118, 152, (2015)
Abstract: Complex organic compounds with benzene/thiophene as pi-segments are inspected as photosensitizers for applications in dye sensitized solar cells. To better understand the charge transport process involved in the dye sensitized solar cells, we used the results of Kohn Sham density functional theory and time-dependent density functional theory (DFT) studies of benzene/thiophene based sensitizers as well as the dye bound to a TiO2 nano cluster. We investigated the electronic structures and UV-Vis spectra of the sensitizers alone and linked to the cluster. We also showed energy level diagrams, the major transitions of molecular orbitals and free energy calculation of the electron transfer from, the sensitizer to the conduction band of the TiO2. The results show that LUMO of the dyes is greater than the conduction band of TiO2 indicating that a full charge transfer from dyes to the conduction band of TiO2 is thermodynamically allowed. The calculated results also indicate that D3 is the most plausible sensitizer due to the most negative Delta G(inject) (0.91 eV) and a larger LHE value (0.95), which results in a higher IPCE.
First author: Feldmann, KO, [P3Se4](+): A Binary Phosphorus-Selenium Cation, CHEMISTRY-A EUROPEAN JOURNAL, 21, 9697, (2015)
Abstract: Although a fairly large number of binary group 15/16 element cations have been reported, no example involving phosphorus in combination with a group 16 element has been synthesized and characterized to date. In this contribution is reported the synthesis and structural characterization of the first example of such a cation, namely a nortricyclane-type [P3Se4](+). This cation has been independently discovered by three groups through three different synthetic routes, as described herein. The molecular and electronic structure of the [P3Se4](+) cage and its crystal properties in the solid state have been characterized comprehensively by using X-ray diffraction, Raman, and nuclear magnetic resonance spectroscopies, as well as quantum chemical calculations.
First author: Saha, R, Comparative Study on the Noble-Gas Binding Ability of BeX Clusters (X =g SO4, CO3, O), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 6746, (2015)
Abstract: Ab initio computations ate tarried out to assess the noble gas (Ng) binding capability of BeSO4 cluster. We have further compared the stability of NgBeSO(4) with that of the recently detected NgBeCO(3) cluster. The Ng-Be bond in NgBeCO(3) is somewhat weaker than that in NgBeO cluster. In NgBeSO(4), the Ng-Be bond is found to be stronger compared with not only the Ng-Be bond in NgBeCO(3) but also that in NgBeO, except the He case. The Ar-Rn-bound BeSO4 analogues are viable even at room temperature. The Wiberg bond indices of Be-Ng bonds and the degree of electron transfer from Ng to Be are somewhat larger in NgBeSO(4) than those in NgBeCO(3) and NgBeO. Electron density and energy decomposition analyses are performed in search of the nature of interaction in the Be-Ng bond in NgBeSO(4). The orbital energy term (Delta E-orb) contributes the maximum (ca. 80-90%) to the total attraction energy. The Ar/Kr/Xe/Rn-Be bonds in NgBeSO(4) could be of partial covalent type with a gradual increase in covalency along Ar to Rn.
First author: Jakobsen, HJ, High-Field O-17 MAS NMR Reveals (1)J(O-17-I-127) with its Sign and theg NMR Crystallography of the Scheelite Structures for NaIO4 and KIO4, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 14434, (2015)
Abstract: High-field, ambient-temperature (AT) O-17 MAS NMR spectra of the tetraoxoanion IO4 in NaIO4- and KIO4 exhibit unusual line-shape features for the central transition (CT), which so far have not been observed in any second-order broadened line shape for the CT of a quadrupolar nucleus. These features are caused by an unusually large isotropic (1)J(O-17-I-127) spin coupling (similar to 500 Hz) and appear like teeth-on-a-saw. This study reports interesting results obtained from optimized fitting of the spectra using our recently described XSTARS software. The results include determination of a positive sign for (1)J(O-17-I-127) (= +500 Hz), an unusual observation in solid-state NMR. NMR crystallography shows a very precise correlation between extraordinary small changes for the O-17 asymmetry parameter (eta(Q)) and changes for a tetrahedral O-I-O angle upon distortion from an ideal tetrahedron. Similarly, the spectral analysis shows that the NMR crystallography requires the principal axes V-zz(O-17) and delta(zz)(O-17) of the PAS for these tensors are both almost along the I-O bond. All the experimental data are in excellent agreement with our ADF and CASTEP calculations.
First author: D'Elia, V, Cooperative Effect of Monopodal Silica-Supported Niobium Complex Pairsg Enhancing Catalytic Cyclic Carbonate Production, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 7728, (2015)
Abstract: Recent discoveries highlighted the activity, and the intrig-uing, mechanistic features of NIDCl5 as a molecular catalyst for the cycloaddffion, of CO2 and epoxides under ambient cooditions. This hag inSpired the preparation, of novel silica-supported Nb species by reacting a molecular niobium precursor, [NbCf5 center dot OEt2], with Silica dehydroxylated at 700 degrees C (SiO2-700) or at 200 degrees C (SiO2-200) to generate diversetrface complexes. The product of the reaction between SiO2-700 and [NbCl5 center dot OEt2] was identified as a monopodal supported surface species, [equivalent to SiONbCl4 center dot OBt(2)] (1a). The reactions, of SiO2-200 with the niobium precursor, according to two different protocols, generated surface complexes 2a. and 3a, presenting significant, but different,, populations of the monopodal surface complex along with bipodal [(equivalent to SiO)(2)NbCl3 center dot OEt2]. Nb-93 solid-state NMR spectra of 1a-3a and P-31 solid-state NMR On their PMe3 derivatives 1b-3b led to the unambiguous assignment of 1a as a single-site monopodal Nb species, while 2a and 3a were found to present two distinct surface-supported components, with 2a being mostly monopodal [equivalent to SiONbCl4 center dot OEt2] and 3a being mostly bipodal [(equivalent to SiO)(2)NbCl3 center dot OEt2]. A double-quantum/single-quantum 3113 NMR correlation experiment carried out on 2b supported the existence of vicinal Nb centers on the silica surface- for this species. 1a-3a were active heterogeneous catalysts for the synthesis of propylene carbonate from CO, and propylene Oxide under mild catalytic conditions,: the performance of 2a was found to significantly surpass that of la and 3a. With the support of a syStetnatic DFT study Carried' out model silica surfaces, the observed differences in catalytic efficiency were correlated with an unprecedented cooperative effect between two neighboring Nb centers on the surface of 2a. This is in an excellent agreement with our previbils discoveries regarding the mechanism Of NbCl5-catalyzed cycloaddition in the homogeneous phase.
First author: Kilina, S, Light-Driven and Phonon-Assisted Dynamics in Organic and Semiconductorg Nanostructures, CHEMICAL REVIEWS, 115, 5929, (2015)
First author: Werle, C, Stabilization of an Electron-Unsaturated Pd(I)-Pd(I) Unit by Doubleg Hemichelation, ORGANOMETALLICS, 34, 3055, (2015)
Abstract: The competition between conventional coordination and hemichelation of a Pd(II) center of three different palladacycles was probed by reacting the tricarbonyl(eta(6)-3-phenylprop-1-enyl)chromium anion with mu-chloro-bridged palladacycles. Structural X-ray diffraction analysis indicates that the main products of the reaction are conventional (eta(3)-allyl)Pd(II) complexes. The latter display significant dynamic behavior in solution, as suggested by H-1 NMR spectroscopy. According to DFT calculations this dynamic behavior can be related to conformational equilibria and to possible chemical exchanges leading to Pd(II) hemichelates. The (eta(3)-allyl)Pd(II) complexes convert readily to homoleptic bis-chelates of Pd(II) and to a bis-hemichelate of a Pd(I)-Pd(I) unit via a reductive disproportionation reaction. The latter Pd(I)-Pd(I) complex bears structural features very similar to those of electron-saturated bis(mu-allyl)-bridged Pd(I) complexes in the literature: the Pd-Pd interaction is only weakly covalent and is dominated by noncovalent attractive interactions, as revealed by NCI analyses. The incipient covalent interaction of the Pd(I) centers with CO ligands of the Cr(CO)(3) moieties is too weak to significantly hinder the motion of the metalcarbonyl rotor in solution, which leaves each Pd center formally unsaturated with a 14-valence-electron count. DFT investigations sustained by QTAIM, NCI, ELF, and ETS-NOCV analyses suggest the predominance of noncovalent attractive forces in the stabilization of the bis(mu-allyl)-bridged Pd(I) Pd(I) complex.
First author: Bazzi, S, Designing a New Class of Bases for Nucleic Acid Quadruplexes andg Quadruplex-Active Ligands, CHEMISTRY-A EUROPEAN JOURNAL, 21, 9414, (2015)
Abstract: A new class of quadruplex nucleobases, derived from 3-deazaguanine, has been designed for various applications as smart quadruplex ligands as well as quadruplex-based aptamers, receptors, and sensors. An efficient strategy for modifying the guanine quadruplex core has been developed and tested by using quantum chemistry methods. Several potential guanine derivatives modified at the 3- or 8-position or both are analyzed, and the results compared to reference systems containing natural guanine. Analysis of the formation energies (BLYP-D3(BJ)/def2-TZVPP level of theory, in combination with the COSMO model for water) in model systems consisting of two and three stacked tetrads with Na+/K+ ion(s) inside the internal channel indicates that the formation of structures with 3-halo-3-deazaguanine bases leads to a substantial gain in energy, as compared to the corresponding reference guanine complexes. The results cast light on changes in the noncovalent interactions (hydrogen bonding, stacking, and ion coordination) in a quadruplex stem upon modification of the guanine core. In particular, the enhanced stability of the modified quadruplexes was shown to originate mainly from increased – stacking. Our study suggests the 3-halo-3-deazaguanine skeleton as a potential building unit for quadruplex systems and smart G-quadruplex ligands.
First author: Artiukhin, DG, Excitation energies from frozen-density embedding with accurateg embedding potentials, JOURNAL OF CHEMICAL PHYSICS, 142, 9414, (2015)
Abstract: We present calculations of excitation energies within the time-dependent density functional theory (TDDFT) extension of frozen-density embedding (FDE) using reconstructed accurate embedding potentials. Previous applications of FDE showed significant deviations from supermolecular calculations; our current approach eliminates one potential error source and yields excitation energies of generally much better agreement with Kohn-Sham-TDDFT. Our results demonstrate that the embedding potentials represent the main error source in FDE-TDDFT calculations using standard approximate kinetic-energy functionals for excitations localized within one subsystem.
First author: Alvarez, JR, DNA/RNA transverse current sequencing: intrinsic structural noise fromg neighboring bases, FRONTIERS IN GENETICS, 6, 9414, (2015)
Abstract: Nanopore DNA sequencing via transverse current has emerged as a promising candidate for third-generation sequencing technology. It produces long read lengths which could alleviate problems with assembly errors inherent in current technologies. However, the high error rates of nanopore sequencing have to be addressed. A very important source of the error is the intrinsic noise in the current arising from carrier dispersion along the chain of the molecule, i.e., from the influence of neighboring bases. In this work we perform calculations of the transverse current within an effective multi-orbital tight-binding model derived from first-principles calculations of the DNA/RNA molecules, to study the effect of this structural noise on the error rates in DNA/RNA sequencing via transverse current in nanopores. We demonstrate that a statistical technique, utilizing not only the currents through the nucleotides but also the correlations in the currents, can in principle reduce the error rate below any desired precision.
First author: Noguchi, Y, Pressure Modulation of Backbone Conformation and Intermolecular Distanceg of Conjugated Polymers Toward Understanding the Dynamism ofg pi-Figuration of their Conjugated System, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 7219, (2015)
Abstract: Continuous tuning of the backbone conformation and interchain distance of a pi-conjugated polymer is an essential prerequisite to unveil the inherent electrical and optical features of organic electronics. To this end, applying pressure in a hydrostatic medium or diamond anvil cell is a facile approach without the need for side-chain synthetic engineering. We report the development of high-pressure, time-resolved microwave conductivity (HP-TRMC) and evaluation of transient photoconductivity in the regioregular poly(3-hexylthiophene) (P3HT) film and its bulk hetero-junction blend with methanofullerene (PCBM). X-ray diffraction experiments under high pressure were performed to detail the pressure dependence of pi-stacking and interlamellar distances in P3HT crystallites and PCBM aggregates. The HP-TRMC results were further correlated with high-pressure Raman spectroscopy and density functional theory calculation. The increased HP-TRMC conductivity of P3HT under pressure was found to be relevant to the planarity of the backbone conformation and intramolecular hole mobility. The effects of pressure on the backbone planarity are estimated to be similar to 0.3 kJ mol(-1) based on the compressibility derived from the X-ray diffraction under high pressure, suggesting the high enough energy to cause modulation of the planarity in terms of the Landau-de Gennes free energy of isolated P3HT chains as 0.23 kJ mol(-1). In contrast, the P3HT:PCBM blend showed a simple decrease in photoconductivity irrespective of the identical compressive behavior of P3HT. A mechanistic insight into the interplay of intra- and intermolecular mobilities is a key to tailoring the dynamic pi-figuration associated with electrical properties, which may lead to the use of HP-TRMC for exploring divergent pi-conjugated materials at the desired molecular arrangement and conformation.
First author: Ramos, P, Performance of Frozen Density Embedding for Modeling Hole Transferg Reactions, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 7541, (2015)
Abstract: We have carried out a thorough benchmark of the frozen density-embedding (FDE) method for calculating hole transfer couplings. We have considered 10 exchange correlation functionals, 3 nonadditive kinetic energy functionals, and 3 basis sets. Overall, we conclude that with a 7% mean relative unsigned error, the PBE and PW91 functionals coupled with the PW91k nonadditive kinetic energy functional and a TZP basis set constitute the most stable and accurate levels of theory for hole transfer coupling calculations. The FDE-ET method is found to be an excellent tool for computing diabatic couplings for hole transfer reactions.
First author: Koldemir, U, Molecular Design for Tuning Work Functions of Transparent Conductingg Electrodes, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 6, 2269, (2015)
Abstract: In this Perspective, we provide a brief background on the use of aromatic phosphonic acid modifiers for tuning work functions of transparent conducting oxides, for example, zinc oxide (ZnO) and indium tin oxide (ITO). We then introduce our preliminary results in this area using conjugated phosphonic acid molecules, having a substantially larger range of dipole moments than their unconjugated analogues, leading to the tuning of ZnO and ITO electrodes over a 2 eV range as derived from Kelvin probe measurements. We have found that these work function changes are directly correlated to the magnitude and the direction of the computationally derived molecular dipole of the conjugated phosphonic acids, leading to the predictive power of computation to drive the synthesis of new and improved phosphonic acid ligands.
First author: Mastrorilli, P, Multinuclear Solid-State NMR and DFT Studies on PhosphanidoBridgedg Diplatinum Complexes, INORGANIC CHEMISTRY, 54, 5855, (2015)
Abstract: Multinudear (P-31, Pt-195, F-19) solid-state NMR experiments on (nBu(4)N)(2)[C6F5)(2)Pt(mu-PPh2)(2)Pt(C6F5)(2)] (1), [(C6F5)(2)Pt(mu-PPh2)(2)Pt(C6F5)(2)] (Pt-Pt) (2), and cis-Pt(C6F5)(2)(PHPh2)(2) (3) were carried out under cross-polarization/magic-angle-spinning conditions or with the crosspolarization/Carr Purcell Meiboom Gill pulse sequence. Analysis of the principal components of the P-31 and Pt-195 chemical shift (CS) tensors of 1 and 2 reveals that the variations observed comparing the isotropic chemical shifts of 1 and 2, commonly referred to as "ring effect", are mainly due to changes in the principal components oriented along the direction perpendicular to the Pt2P2 plane. DFT calculations of P-31 and Pt-195 CS tensors confirmed the tensor orientation proposed from experimental data and symmetry arguments and revealed that the different values of the isotropic shieldings stem from differences in the paramagnetic and spin-orbit contributions.
First author: Suresh, D, Luminescent Di- and Trinuclear Boron Complexes Based on Aromaticg Iminopyrrolyl Spacer Ligands: Synthesis, Characterization, andg Application in OLEDs, CHEMISTRY-A EUROPEAN JOURNAL, 21, 9133, (2015)
Abstract: New bis- and tris(iminopyrrole)-functionalized linear (1,2-(HNC4H3-C(H)N)(2)-C6H4 (2), 1,3-(HNC4H3-C(H)N)(2)-C6H4 (3), 1,4-(HNC4H3-C(H)N)(2)-C6H4 (4), 4,4-(HNC4H3-C(H)N)(2)-(C6H4-C6H4) (5), 1,5-(HNC4H3C-(H)N)(2)-C10H6 (6), 2,6-(HNC4H3C-(H)N)(2)-C10H6 (7), 2,6-(HNC4H3C-(H)N)(2)-C14H8 (8)) and star-shaped (1,3,5-(HNC4H3-C(H)N-1,4-C6H4)(3)-C6H3 (9)) -conjugated molecules were synthesized by the condensation reactions of 2-formylpyrrole (1) with several aromatic di- and triamines. The corresponding linear diboron chelate complexes (Ph2B[1,3-bis(iminopyrrolyl)-phenyl]BPh2 (10), Ph2B[1,4-bis(iminopyrrolyl)-phenyl]BPh2 (11), Ph2B[4,4-bis(iminopyrrolyl)-biphenyl]BPh2 (12), Ph2B[1,5-bis(iminopyrrolyl)-naphthyl]BPh2 (13), Ph2B[2,6-bis(iminopyrrolyl)-naphthyl]BPh2 (14), Ph2B[2,6-bis(iminopyrrolyl)-anthracenyl]BPh2 (15)) and the star-shaped triboron complex ([4,4,4-tris(iminopyrrolyl)-1,3,5-triphenylbenzene](BPh2)(3) (16)) were obtained in moderate to good yields, by the treatment of 3-9 with B(C6H5)(3). The ligand precursors are non-emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the -conjugation length. The photophysical properties of the luminescent polyboron compounds were measured, showing good solution fluorescence quantum yields ranging from 0.15 to 0.69. DFT and time-dependent DFT calculations confirmed that molecules 10 and 16 are blue emitters, because only one of the iminopyrrolyl groups becomes planar in the singlet excited state, whereas the second (and third) keeps the same geometry. Compound 13, in which planarity is not achieved in any of the groups, is poorly emissive. In the other examples (11, 12, 14, and 15), the LUMO is stabilized, narrowing the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), and the two iminopyrrolyl groups become planar, extending the size of the -system, to afford green to yellow emissions. Organic light-emitting diodes (OLEDs) were fabricated by using the new polyboron complexes and their luminance was found to be in the order of 2400cdm(-2), for single layer devices, increasing to 4400cdm(-2) when a hole-transporting layer is used.
First author: Mingos, DMP, A theoretical analysis of ambivalent and ambiphilic Lewis acid/basesg with symmetry signatures, COORDINATION CHEMISTRY REVIEWS, 293, 2, (2015)
Abstract: This review provides a theoretical underpinning of previously published definitions of ambidentate, ambivalent and ambiphilic ligands. The study encompasses ambivalent ligands such as NO, NR, N2R; ambiphilic molecules such as SO2, I-2 and ambiphilic transition metal complexes, e.g. [Pt(PCy3)(2)]. These ambivalent molecules adopt alternative geometries which depend primarily on the number of electrons which they formally donate or accept. The theoretical analysis focuses initially on those complexes where the same ligand displays ambivalent properties within the same molecule in order to define the energetics of their interconversion. These square-pyramidal complexes provide a test-bed for generating data which throws light on the relative abilities of ambivalent ligands to adopt linear or bent geometries. The ligands were compared with NO and their relative abilities were placed in the following order PO> PH2 > N2H >SO2 > NO >NH2 > NS. The linear nitrosyl ligand does not exert a trans-influence and this property has been contrasted with the nitrido-ligand which shows a large trans-influence. The conversion of NO to a non-linear geometry results in a strong trans-influence and this has significant catalytic and biological importance. Calculations on octahedral palladium complexes have been used to order the trans-influences of ambivalent ligands when they adopt their alternative symmetry signatures. The relative trans-influences are NO> PH2 >NS > N2H > NH2. The interconversion of linear and bent dinitrosyls provides an interesting inorganic example of valence tautomerism and this is noted as a general characteristic of ambivalent and ambiphilic ligands. The soft energy surface associated with these interconversions leads to the experimentally verified fluxional process. The energetics of adduct formation by ambiphilic ligands has been studied using a series of SO2 complexes of palladium and platinum and the results contrasted with adducts of SO2 with main group Lewis acids and bases. The isomers {(PH3)(2)M(SO2)p}(16) and {(PH3)(2)M(SO2)np)(14) are calculated to have very similar energies and the relative stabilities of analogous isomers may be manipulated by varying the bite angle of the phosphine ligands in {[(PH2)(2)CnH2n]M(SO2)}.
First author: Sundberg, J, Accessing iron amides from dimesityliron, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 786, 40, (2015)
Abstract: A new phase of dimesityliron has been crystallized from diethylether; the crystal structure shows a dinuclear complex with co-crystallized solvent. Crystalline [Fe-2(mes)(2)(mu(2)-mes)(2)]center dot Et2O is a convenient starting material and reacts with di(2-pyridyl) amine to yield rare iron di(2-pyridyl) amido complexes. Crystal structures of air-sensitive [Fe-2(mes)(2)(dpa)(2)], [Fe-2(dpa)(3)Cl] and [Fe-4(dpa)(6)O] were determined. [Fe-4(dpa)(6)O] is known, and the dinuclear complexes [Fe-2(mes)(2)(dpa)(2)] and [Fe-2(dpa)(3)Cl] represent only the second and third reports of homometallic iron dpa(-) complexes. Long Fe. Fe distances of 3.043(1) and 3.104(2) angstrom in [Fe-2(mes)(2)(dpa)(2)] and [Fe-2(dpa)(3)Cl], respectively, and very unsymmetrically coordinated amido groups, indicate that the iron atoms are not involved in M-M bonding. This fact, and the relatively low coordination numbers of the high spin Fe(II) atoms are consistent with sensitivity of these compounds towards O-2. DFT calculations were employed to rationalize the formation of the unusual architectures displayed by the dpa(-) complexes of iron.
First author: McCready, MS, The Platinum Center is a Stronger Nucleophile than the Free Nitrogeng Donors in a Dimethylplatinum Complex with a Dipyridylpyridazine Ligand, ORGANOMETALLICS, 34, 2261, (2015)
Abstract: The ligand 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine (6-dppd) contains two potential chelate groups, but it coordinates to only one dimethylplatinum group in forming the complex [PtMe2(6-dppd)], 1. Complex 1 contains a free pyridyl and a free pyridazine nitrogen donor, but it fails to coordinate to ZnCl2 or to CuCl to give a bimetallic complex. Complex I reacted with mercury(II) salts HgX2 (X = Cl, Br, OAc), not by coordination but by oxidative addition to the dimethylplatinum(II) center to give the platinum(IV) complexes [PtX(HgX)Me-2(6-dppd)]. Complex 1 reacted with bromine or iodine by trans oxidative addition to give [PtX2Me2(6-dppd)], X = Br or I, but, when X = I, a more complex sequence of reactions also gave rise to products of cis oxidative addition and to the products [PtIMe3(6-dppd)] and [PtI3Me(6-dppd)], which arise through a methyl group transfer reaction. Complex 1 reacted with alkyl halides RX by trans oxidative addition to give [PtXRMe2(6-dppd)], R = Me, X = I; R = CH2Ph, X = Br; R = CH2-4-C6H4-CH2Br, X = Br. The cleavage of methyl groups from complex 1 by DCl gave a mixture of all isotopomers of methane, CH4-nDn, indicating ready equilibration between hydrido(methyl)platinum(IV) and methaneplatinum(II) complex intermediates.
First author: Evans, DA, Aggregation-Induced Emission of Bis(imino)acenaphthene Zinc Complexes:g Photophysical Tuning via Methylation of the Flanking Aryl Substituents, ORGANOMETALLICS, 34, 2422, (2015)
Abstract: Bis(imino)acenaphthene zinc complexes with methylated aryl substituents have been examined from the standpoint of their photoluminescent properties. Although complexes 1-4 proved to be nonemissive in solution, complexes 1 and 2 were found to emit via an aggregation-induced emission pathway. On the other hand, complexes 3 and 4 were found to be nonemissive in the solid state. Detailed crystallographic studies of complexes 1-4 provided valuable insights into the structural differences between the emissive (1 and 2) and nonemissive complexes (8 and 4), particularly with respect to their molecular Structures and crystal-packing environments. TD-DFT theoretical calculations were carried out and were found to support the hypothesis that the phosphorescent emissions of 1 and 2 are due to the existence of intermolecular pi-stacking interactions within the crystal lattices. Finally, a series of solvatomorphs of complexes 1 and 2 were synthesized and their emissive properties were studied.
First author: Taylor, MJ, beta-Diketiminato Organolead Complexes: Structures, Pb-207 NMR, andg Hammett Correlations, ORGANOMETALLICS, 34, 2515, (2015)
Abstract: The synthesis, structure, and spectroscopic details of a series of beta-diketiminato lead(II) alkyl complexes are described. The Hammett correlation between the Pb-207 NMR. chemical shifts sigma(para). Hammett constant was examined computationally and found to be due to the paramagnetic shielding contribution, whereas the diamagnetic and spin-orbit coupling contributions remained fairly constant across this series of compounds.
First author: Vlahovic, F, Assessment of TD-DFT and LF-DFT for study of d – d transitions in firstg row transition metal hexaaqua complexes, JOURNAL OF CHEMICAL PHYSICS, 142, 2515, (2015)
Abstract: Herein, we present the systematic, comparative computational study of the d – d transitions in a series of first row transition metal hexaaqua complexes, [M(H2O)(6)](n+) (M2+/3+ = V2+/3+, Cr2+/3+, Mn2+/3+, Fe2+/3+, Co2+/3+, Ni2+) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d(2), d(4), and low-spin d(6) complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d(5) complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.
First author: Priyanka, B, Toward Designing Efficient Multifunctional Bipolar Molecules: DFT Studyg of Hole and Electron Mobilities of 1,3,4-Oxadiazole Derivatives, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 12251, (2015)
Abstract: With a general aim to analyze molecules containing 1,3,4-oxadiazole moiety for charge transport in organic light-emitting diode devices, in this study we use density functional theory methods to compute reorganization energies, transfer integrals, and hole and electron mobilities of a very large number of symmetrically substituted small and large oxadiazole derivatives retrieved from Cambridge Structural Database. The study reveals that for the majority of small planar molecules, the reorganization energies are large, and the transfer integral plays a crucial role in the charge transport. In the case of large planar molecules, small reorganization energies leading to large drift mobility for both hole and electron transport is observed. The detailed analyses of the geometry and molecular orbitals of the molecules along with the pathways in the solid state were performed, which should be helpful for improving the design of oxadiazole derivatives for multifunctional bipolar properties
First author: Azpiroz, JM, First-Principles Modeling of Core/Shell Quantum Dot Sensitized Solarg Cells, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 12739, (2015)
Abstract: We report on the density functional theory (DFT) modeling of core/shell quantum dot (QD) sensitized solar cells (QDSSCs), a device architecture that holds great potential in photovoltaics but has not been fully exploited so far. To understand the working mechanisms of this kind of solar cells, we have investigated ZnSe- and ZnSe/CdS-sensitized TiO2 models. Both the core-only and the core/shell QDs are predicted to strongly adsorb on the oxide surface, driven by the electrostatic interaction between the metal atoms on the QD surface and the O atoms exposed by the oxide substrate. Accordingly, the QD conduction states are strongly mixed with the TiO2 acceptor states, giving rise to bridge states that should funnel the interfacial electron transfer. Accordingly, quite fast electron injection processes are predicted, with computed rates of 135 and 163 fs. The back-electron transfer is much slower for ZnSe/CdS, due to the weak coupling between the newly injected charge and the holes trapped in the sensitizer core. Therefore, the core/shell QDs deliver much better efficiencies. Moreover, the interfacial dipole established between the TiO2-injected electrons and the holes confined in the QD are found to shift the conduction band edge of the oxide, which further improves the performance of the device in terms of the open circuit voltage (V-oc). We believe that this work sets the ground for future computational works in the field, which could in turn guide the fabrication of new device architectures with improved efficiencies.
First author: Kravtsova, AN, Atomic and electronic structure of CdS-based quantum dots, JOURNAL OF STRUCTURAL CHEMISTRY, 56, 517, (2015)
Abstract: The ab initio computer design of the CdS-based quantum dots and the cobalt doped CdS quantum dots is carried out. The characteristics features of the atomic and electronic structures of semiconductor colloidal quantum dots on CdS of different sizes are studied, and the effect of cobalt impurity atoms is estimated. We have proved the sensitivity of the X-ray absorption near-edge structure (XANES) method for the verification of the nanosized atomic structural parameters calculated by the methods of computer modeling for small-scale quantum dots of the CdS family, and for the determination of the local environment parameters of the cobalt atom in the quantum dot.
First author: Guillaumes, L, The Role of Aromaticity, Hybridization, Electrostatics, and Covalency ing Resonance-Assisted Hydrogen Bonds of Adenine-Thymine (AT) Base Pairs andg Their Mimics, CHEMISTRYOPEN, 4, 318, (2015)
Abstract: Hydrogen bonds play a crucial role in many biochemical processes and in supramolecular chemistry. In this study, we show quantum chemically that neither aromaticity nor other forms of assistance are responsible for the enhanced stability of the hydrogen bonds in adenine-thymine (AT) DNA base pairs. This follows from extensive bonding analyses of AT and smaller analogs thereof, based on dispersion-corrected density functional theory (DFT). Removing the aromatic rings of either A or T has no effect on the Watson-Crick bond strength. Only when the smaller mimics become saturated, that is, when the hydrogen-bond acceptor and donor groups go from sp(2) to sp(3), does the stability of the resulting model complexes suddenly drop. Bonding analyses based on quantitative Kohn-Sham molecular orbital theory and corresponding energy decomposition analyses (EDA) show that the stronger hydrogen bonds in the unsaturated model complexes and in AT stem from stronger electrostatic interactions as well as enhanced donor-acceptor interactions in the sigma-electron system, with the covalency being responsible for shortening the hydrogen bonds in these dimers.
First author: Gavara, R, Thermodynamic Aspects of Aurophilic Hydrogelators, INORGANIC CHEMISTRY, 54, 5195, (2015)
Abstract: The complexes [Au(4-pyridylethynyl)(phosph)] (phosph = PTA (1), DAPTA (2)) are known to produce supramolecular aggregates and gels in water. We studied the impact of these aggregation processes in the absorption spectra, (1)H NMR (at different temperatures and concentrations), and DLS and estimated the equilibrium constant for a single step aggregation of the molecule (K = 26760 and 2590 M-1 for 1 and 2, respectively, at 25 degrees C). We present spectroscopic evidence for the presence of (AuAu)-Au-… contacts in the aggregates: the recorded changes on H-1 NMR and the appearance of new absorption bands assigned to (sigma*(AU….AU-)sigma*) have been attributed to the short ((AuAu)-Au-…) average distances in the aggregates. Relativistic density functional theory computations support the existence of short (AuAu)-Au-… distances and reveal charge-transfer in the aurophilic interactions. The free energy for a single step aggregation was calculated from the experimental data, and the value obtained (Delta G similar to -20 kJ/mol) is in good agreement with the expected values in the order of the energies found for hydrogen bonds. The DFT computations confirm the experimental findings that aggregation of monomer 1 is stronger than the aggregation of monomer 2 and the existence of aurophilic interactions.
First author: Yao, J, Highly Valence-Diversified Binuclear Uranium Complexes of a Schiff-Baseg Polypyrrolic Macrocycle: Prediction of Unusual Structures, Electronicg Properties, and Formation Reactions, INORGANIC CHEMISTRY, 54, 5438, (2015)
Abstract: On the basis of relativistic density functional theory Calculations, homo- and heterovalent binuclear,uranium :complexes of a polypyrrolic macrocycle in a U-O-U bridging fashion have been investigated. These complexes show a Variety of oxidation states for uranium ranging from III to VI, which have been confirmed by the calculated electron-spin density on each metal center. An equatorially 5-fold uranyl coordination mode is suitable for hexavalent uranium complexes, while silylation of the uranyl oxo is favored by pentavalent uranium. Uranyl oxo ligands are not required anymore for the coordination environment of tetra- and trivalent uranium because of their replacement by strong donors such as tetrahydrofuran and iodine. Optimization, of binuclear U-VI-U-III complexes with various,coordinating modes of U-III, donor and-donor types reveals that 0.5-1.0 electron his been transferred from U-III to U-VI. Consequently, U-V-U-IV complexes are more favorable. Electronic structures and formation reactions of several representative uranium complexes were calculated. For example, a 5f-based sigma(U-U) bonding Orbital is found in the diuranium(IV) complex, rationalizing that fact that it shows the shortest U-U distance (3.82 angstrom) among the studied binuclear complexes.
First author: Morrison, G, Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study ofg Uranium(IV)-Containing A(2)USi(6)O(15) (A = K, Rb) with an Intriguingg Green-to-Purple, Crystal-to-Crystal Structural Transition in the Kg Analogue,INORGANIC CHEMISTRY, 54, 5504, (2015)
Abstract: The flux growth of uranium(IV) oxides presents several challenges, and to the best of our knowledge, only one example has ever been reported. We succeeded in growing two new reduced uranium silicates A(2)USi(6)O(15) (A = K,. Rh) under flux growth conditions in sealed copper tubes. The compounds crystallize hi a new structure type with space group C2/c and lattice parameters a = 24.2554(8) angstrom, b = 7.0916(2) angstrom, c = 17.0688(6) angstrom, beta = 97.0860(6)degrees (K) and a = 24.3902(8) angstrom, b = 7.1650(2) angstrom, c = 17.2715(6) angstrom, beta = 96.8600(6)degrees (Rb). A(2)USi(6)O(13) (A = K, Rb) are isocompositional to a previously reported Cs2USi6O15, and the two structures are compared K2USi6O15 undergoes an interesting crystal-to-crystal structural phase transition at T approximate to 225 K to a triclinic structure, which is accompanied by an intense color change. The magnetic properties of A(2)USi(6)O(15) (A = K, Rh, Cs) ate reported and differ from the magnetism observed in other U4+ compounds. Calculations are performed on the (UO6)(-8) clusters of K2USi6O15 to study the cause of these unique magnetic properties.
First author: Gil, A, How the Intercalation of Phenanthroline Affects the Structure,g Energetics, and Bond Properties of DNA Base Pairs: Theoretical Studyg Applied to Adenine-hymine and Guanine-ytosine Tetramers, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 2714, (2015)
Abstract: The effects of phenanthroline (phen) intercalation on the structure, energetics, and bonding of adenine-thymine and guanine-cytosine tetramers (A-T/T-A and G-C/C-G) were studied through density functional theory (DFT) using functionals that were recently improved to consider the effect of dispersion: forces. Our results given by energy decomposition analysis Show that the dispersion contribution, Delta E-disp, is the most important contribution to the interaction energy, Delta E-int. However,, it is not enough to compensate the Pauli repulsion term, Delta E-Pauli, and the roles of the orbital contribution, Delta E-orb, and, in particular, the electrostatic contribution, Delta E-elstat, become crucial for the stabilization of the structures in the intercalation process. On the other hand, for G-C/C-G systems, hydrogen-bonding (HB) interactions are more important than stacking (S) interactions, whereas for A-T/T-A systems, HB and S become competitive. Moreover, intercalation produces important changes not only in the hydrogen bonds of base pairs, because S and HB are deeply connected, but also in other characteristic geometric parameters of the base pairs.
First author: Cominetti, A, Polymer solar cells based on poly(3-hexylthiophene) and fullerene:g Pyrene acceptor systems, MATERIALS CHEMISTRY AND PHYSICS, 159, 46, (2015)
Abstract: The replacement of widely used fullerene derivatives, e.g. [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), with unfunctionalized C60 and C70 is an effective approach to reduce the costs of organic photovoltaics. However, solubility issues of these compounds have always represented an obstacle to their use. In this study, bulk-heterojunction solar cells made of poly(3-hexylthiophene) donor polymer, C60 or C70 acceptors and a pyrene derivative (1-pyrenebutiric acid butyl ester) are reported. Butyl 1-pyrenebutirate limits the aggregation of fullerenes and improves the active layer morphology, plausibly due to the formation of pyrene-fullerene complexes which, in the case of pyrene-C70, were also obtained in a crystalline form. Maximum power conversion efficiencies of 1.54% and 2.50% have been obtained using, respectively, C60 or C70 as acceptor. Quantum mechanical modeling provides additional insight into the formation of plausible supermolecular structures via pi-pi interactions and on the redox behaviour of pyrene-fullerene systems.
First author: Vent-Schmidt, T, Investigation of thorium hydride fluorides by matrix-isolationg spectroscopy, JOURNAL OF FLUORINE CHEMISTRY, 174, 2, (2015)
Abstract: Following the successful preparation of HUF through the reaction of laser ablated uranium atoms with HF in excess noble gases, we continue the investigation of actinide atom reactions with HF. Herein we report the reaction products of laser ablated thorium atoms with HF as well as supporting quantum chemical calculations and a discussion of the bonding in HThF and higher oxidation state molecules. The results of this study are compared to previous results obtained in similar uranium reactions.
First author: Chistyakov, VA, Physical consequences of the mitochondrial targeting of single-walledg carbon nanotubes probed computationally, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 70, 198, (2015)
Abstract: Experiments by F. Zhou and coworkers (2010) [16] showed that mitochondria are the main target of the cellular accumulation of single walled carbon nanotubes (SWCNTS). Our in silica experiments, based on geometrical optimization of the system consisting of SWCNT + proton within Density Functional Theory, revealed that protons can bind to the outer side of SWCNT so generating a positive charge. Calculation results allow one to propose the following mechanism of SWCNTs mitochondria! targeting. SWCNTs enter the space between inner and outer membranes of mitochondria, where the excess of protons has been formed by diffusion. In this compartment SWCNTs are loaded with protons and acquire positive charges distributed over their surface. Protonation of hydrophobic SWCNTs can also be carried out within the mitochondrial membrane through interaction with the protonated ubiquinone. Such "charge loaded" particles can be transferred as "Sculachev ions" through the inner membrane of the mitochondria due to the potential difference generated by the inner membrane. Physiological consequences of the described mechanism are discussed.
First author: Seidu, I, Applications of Time-Dependent and Time-Independent Density Functionalg Theory to Rydberg Transitions, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 5107, (2015)
Abstract: We have benchmarked the performance of time,independent density functional theory (Delta SCF and. RSCF-CV-DFT) in Studies on Rydberg transitions employing five different standard functionals and a diffuse basis. Our survey is based on 71 triplet or singlet Rydberg transitions distributed over nine different Species: CO (7), CH2O (8), C2H2 (8), H2O (10), C2H4 (13), Be (6), Mg (6), and Zn (8). The best performance comes from the long-range corrected functional LCBP86 (omega = 0.4.) with an average root-mean-square deviation (RMSD) of 0.23 eV. Of similar accuracy are LDA and B3LYP, both with a RMSD of 0.24 eV. The largest RMSD of 0.32 eV comes from BP86 and LCBP86* (omega = 0:75). The performance of Delta SCF is considerably better than that of adiabatic time-dependent density functional theory (ATDDFT) and matches that of highly optimized long-range corrected functionals. However, it is not as accurate as ATDDFT based on highly tuned functionals: The reasonable success of Delta SCF is based on its well-documented ability to afford good estimates of ionization potentials (IP) and electron affinities (EA) even for simple local functionals after orbital relaxation has been taken into account. In ATDDFT based on semilocal functionals, both IP and -EA are poorly described, with errors of up to 5 eV. In the transition energy (Delta E = IP – EA), these errors are canceled to some degree. However, Delta E still carries an error exceeding 1 eV.
First author: Chulhai, DV, Plasmonic Circular Dichroism of 310-and alpha-Helix Using a Discreteg Interaction Model/Quantum Mechanics Method, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 5218, (2015)
Abstract: Plasmonic circular dichroism (CD)of chiral molecules in the near field of plasmonic nanoparticles (NPs) May be used to enhance molecular CD signatures or to induce a CD signal at the plasmon resonance. A recent few-states theory explored these effects for model systems and showed an orientation dependence of the Sign of the induced pp signal for spherical NPs. Here, we use the discrete interaction model/quantum. mechanical (DIM/QM) method to simulate the CD and plasmonic CD of the and alpha-helix conformations of a short alanine peptide. We find that the interactions between the molecule and the plasm:on lead to significant changes in the CD spectra. In the plasmon region, we find that the sign of the CD depends strongly on the orientation of the molecule as well: as specific interactions with the NP through image dipole effects. A small enhancement of the CD is found in the molecule region of the spectrum, however, the molecular signatures maybe significantly altered through interactions with the NP. We also show that the image dipole effect can result in induced plasmonic CD even for achiral molecules. Overall, we find that the specific interactions with the NP can lead to large changes to the CD spectrum that complicates the interpretation of the results.
First author: Chen, X, Why Do Boron and Nitrogen Doped alpha- and gamma-Graphyne Exhibitg Different Oxygen Reduction Mechanism? A First-Principles Study, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 11493, (2015)
Abstract: The oxygen reduction reaction mechanisms catalyzed by B, N doped alpha- and gamma-graphyne were investigated in detail by DFT methods, in which doped graphynes with different configurations could exhibit different oxygen reduction reaction activities. The B or N single-doped alpha-B(1)G and a-N(2)G and co-doped alpha-B(1)N(2)G and alpha-B(1)N(3)G show relatively low catalytic activities, owing to their unfavorable reversible potential in oxygen reduction steps, while the co-doped alpha-B(1)N(4)G with separated B, N and single-doped gamma-NG show relatively high activities. With the further increasing of the N content, the onset potential is largely enhanced to 0.413 V for alpha-B-1(N-4)(3)G. The origin of activity of alpha-B-1(N-4)(3)G and gamma-NG is attributed to the higher energy levels of the highest occupied molecular orbital and/or more positive charge (spin) density distributions.
First author: Biasiolo, L, Diffusion NMR measurements on cationic linear gold(I) complexes, POLYHEDRON, 92, 52, (2015)
Abstract: In the last years, it has been demonstrated that the anion plays a key role in gold(I) catalysis, affecting yield, regio- and stereo-selectivity of processes. In order to perform such activity, necessarily the anion has to locate itself close to the reaction center. In this contribution, the level of aggregation of cationic linear gold complexes bearing different ligands, such as phosphines and carbenes, is studied by diffusion PGSE (Pulsed field Gradient Spin Echo) NMR spectroscopy as a function of concentration and solvent. It is found that functional groups, which establish specific interactions with the anion, such as -NH or polarized -CH moieties, strongly influence the self-aggregation of gold(I) complexes: ion pairs are the predominant species in solution, but ion quadruples also form in apolar solvents only when -NH or polarized -CH moieties are present in the ligand. In the absence of those functional groups free ions are present in solution with a small amount of ion pairs. Interestingly, the presence of an extended aromatic group on the cation leads to dicationic adducts and ion triples, which are held together by pi-pi stacking interactions. When more than one functional group is present, F-19, H-1 HOESY (Heteronuclear Overhauser Effect SpectroscopY) NMR experiments and DFT coulomb potential maps are used to check which group establishes the strongest interaction with the anion.
First author: Jupp, AR, Exploiting the Bronsted Acidity of Phosphinecarboxamides for theg Synthesis of New Phosphides and Phosphines, CHEMISTRY-A EUROPEAN JOURNAL, 21, 8015, (2015)
Abstract: We demonstrate that the synthesis of new N-functionalized phosphinecarboxamides is possible by reaction of primary and secondary amines with PCO- in the presence of a proton source. These reactions proceed with varying degrees of success, and although primary amines generally afford the corresponding phosphinecarboxamides in good yields, secondary amines react more sluggishly and often give rise to significant decomposition of the 2-phosphaethynolate precursor. Of the new N-derivatized phosphinecarboxamides available, PH2C(O)NHCy (Cy=cyclohexyl) can be obtained in sufficiently high yields to allow for the exploration of its BrOnsted acidity. Thus, deprotonating PH2C(O)NHCy with one equivalent of potassium bis(trimethylsilyl)amide (KHMDS) gave the new phosphide [PHC(O)NHCy](-). In contrast, deprotonation with half of an equivalent gives rise to [P{C(O)NHCy}(2)](-) and PH3. These phosphides can be employed to give new phosphines by reactions with electrophiles, thus demonstrating their enormous potential as chemical building blocks.
First author: Raupach, M, A periodic energy decomposition analysis method for the investigation ofg chemical bonding in extended systems, JOURNAL OF CHEMICAL PHYSICS, 142, 8015, (2015)
Abstract: The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the bonding energy between two fragments (e.g., the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic, Pauli repulsion, and orbital relaxation energies. This is complemented by consideration of dispersion interactions via a pairwise scheme. One major extension toward a previous implementation [Philipsen and Baerends, J. Phys. Chem. B 110, 12470 (2006)] lies in the separate discussion of electrostatic and Pauli and the addition of a dispersion term. The pEDA presented here for an implementation based on atomic orbitals can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy, and k-space sampling. Four typical bonding scenarios for surface-adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H-2 on M(001), M = Pd, Cu), and semiconducting (CO and C2H2 on Si(001)) substrates. These examples cover diverse substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence that the pEDA will be a powerful tool for the analysis of surface-adsorbate bonding in the future, enabling the transfer of concepts like ionic and covalent bonding, donor-acceptor interaction, steric repulsion, and others to extended systems.
First author: Schweicher, G, Bulky End-Capped [1]Benzothieno[3,2-b]benzothiophenes: Reachingg High-Mobility Organic Semiconductors by Fine Tuning of the Crystallineg Solid-State Order, ADVANCED MATERIALS, 27, 3066, (2015)
First author: Steenbock, T, Photoswitching Behavior of a Cyclohexene-Bridged versus ag Cyclopentene-Bridged Dithienylethene System, CHEMPHYSCHEM, 16, 1491, (2015)
Abstract: Photoswitching is an intriguing way of incorporating functionality into molecules or their subunits. Dithienylethene switches are particularly promising, but have so far mostly been studied with five-membered ring (cyclopentenyl) backbones. We aim at comparing the switching properties of backbones with five and six carbon atoms in the ring. A major advantage is that cyclohexenyl rings offer new options for chiral functionalization. A slight change in the reaction conditions of a McMurry ring closure reaction leads to the formation of dithienyl derivatives with a cyclohexene backbone in reasonable yield. Density functional theory calculations were carried out, demonstrating the similarity of both compounds. Experimental results confirm the theoretical outcomes.
First author: Cheng, Y, First-principle study of the structural, electronic and opticalg properties of defected amorphous silica, JOURNAL OF NON-CRYSTALLINE SOLIDS, 416, 36, (2015)
Abstract: The oxygen-excess structures include oxygen dangling bond, peroxy linkage (POL), peroxy radical (FOR) and interstitial oxygen molecule or ozone molecule defects, while the oxygen-deficient structures include neutral oxygen vacancy, E' center and oxygen double-bond. For both the undefected and the various defected structures, the electronic and optical properties are calculated by plane-wave pseudo potential density functional theory. The oxygengdeficient defected structures lead to the remarkable increases in the density of states (DOS) at.the top of valence band and near the bottom of the conduction band. The oxygen-excess defected structures change the distribution of defect levels and there appear new levels between the valence band and conduction band. All the defects lead to the increase of static dielectric constants and the enhancing absorption in the low energy range. Absorption peaks can be observed below 2 eV for NBOHC defected structures. Though the energy loss is generated at the lower energy region, the loss strength below 2 eV for oxygen-excess defected structures is stronger than oxygen-deficient defected structures. During the calculation the dangling bond in the structures are neutralized by hydrogen atoms. This work may give insights into the laser induced damage towards to vitreous silica.
First author: Nasser, N, Quadruple cyclometalation of a diphosphine-dicarboxamide ligand atg platinum(II), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 784, 88, (2015)
Abstract: This work has established the double and quadruple cyclometalation of the ligands 1,3- or 1,4-C6H4(CONHCH2CH2PPh2)(2) (dpipa or dppeta respectively) by either reagent [Pt2Me4(mu-SMe2)(2)], 1, or [Pt(O2CCF3)(2)(SMe2)(2)], 2b, to give complexes containing new PNC-pincer ligands. The major product formed depends primarily on the stoichiometry of the reaction, but also on the reaction conditions. Reaction of a 1:1 mixture of dppeta and 1 followed by crystallization from a solvent mixture containing dmso, gave remarkable quadruple metalation of dppeta in the product [Pt-2(dmso)(2)(mu-kappa(6)-C,C',N,N',P,P'-(CH2)-H-6{C(=O)N(CH2)(2)PPh2}(2))], which contains two PNC-pincer groups. Reaction of a 1:1 mixture of dpipa and 2b gave double metalation of dpipa in the dimeric product [Pt-2{mu-kappa(4)-C,N,P,P'-C6H3(CONH(CH2)(2)PPh2)(CON(CH2)(2)PPh2)}(2)], which contains one PNC-pincer group for each dpipa ligand used. Related reactions were monitored by NMR spectroscopy and gave insight into the reaction sequences involved in the cyclometalation steps. It is argued that phosphine coordination directs a first N-H bond activation and then, in a faster step, that the amido group formed in this step directs an aryl C-H bond activation step, to give double cyclometalation of one arm of the dicarboxamide-diphosphine ligand and that, if stoichiometry allows, this can be followed by similar double cyclometalation of the second arm to give the quadruply cyclometalated ligand.
First author: Luo, HF, Synthesis and Characterization of Gallium-Doped CdSe Quantum Dots, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 10749, (2015)
Abstract: Developing electronic doping of colloidal quantum dots is important for basic science and technology. In this article, the doping of colloidal CdSe quantum dots with gallium atoms is reported. Gallium doping of CdSe quantum dots produces important changes in electronic and optical properties of the material. The gallium doping shows a significant impact on the growth kinetics of quantum dots, which reveals important clues about the mechanism of the gallium dopant incorporation into the CdSe. The results show that the gallium doping significantly impacts the conductivity of CdSe thin film made of the quantum dots as well as the photoluminescence and chemical reactivity of the quantum dots, in agreement with the expected n-type character.
First author: Benhamada, N, Molecular structure, bonding analysis and redox properties of transitiong metal-Hapca [bis(3-aminopyrazine-2-carboxylic acid)] complexes: Ag theoretical study, POLYHEDRON, 91, 59, (2015)
Abstract: Density functional theory (DFT) calculations were carried out on M(Hapca)(2)(H2O)(2) (M = Mn, Fe, Co, Ni and Hapca = bis(3-aminopyrazine-2-carboxylic acid) by means of the BP86 and B3LYP functional using the TZP basis set. The optimized structures were obtained by imposing C-2 or C-i symmetries. The C-i structural arrangement consists of a slightly distorted octahedron centered by a transition-metal with bidentate Hapca ligands situated in equatorial positions and water molecules in axial ones. However, the C-2 structure consists of a distorted arrangement with n con-planar Hapca ligands. The influence induced by including double polarized functions in the (TZ2P) basis set is small on the geometrical parameters. A bonding analysis of these species showed the weakness of M-O(H2O) bonds compared to M-O(Hapca) ones. The obtained MO diagrams showed substantial HOMO-LUMO gaps for the 18-MVE closed-shell configuration. Reduction of M(Hapca)(2)(H2O)(2) led to the loss of the two water molecules, inducing four electrons downwards for [Co](-) and [Ni] species. The calculated ionization potentials (IPs) and electronic affinities (EAs) showed the oxidation and reduction ease of the manganese species contrarily to the cobalt ones. A diffuse function in the basis set (QZ3P-ndiffuse, n = 1 or 2) reduces remarkably the adiabatic electron affinities (AEAs).
First author: Lasser, L, Energy Level Alignment at Titanium Oxide-Dye Interfaces: Implicationsg for Electron Injection and Light Harvesting, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 9899, (2015)
Abstract: We have performed density functional theory calculations to describe the changes in the electronic structure of oligothiophene derivatives equipped with carboxylic acid anchoring groups upon chemical grafting on TiO2 clusters. The adsorption promotes a partial pinning effect for the lowest unoccupied molecular orbital of the dye, i.e., a LUMO energy level alignment with respect to the TiO2 conduction band edge (CBE) irrespective of the oligothiophene length, which we ascribe to a strong hybridization between the dye discrete (LUMO) level and the cluster conduction band (CB). This is borne out by the fact that no pinning is observed, when decoupling the conjugated segment from the metal oxide substrate, e.g., by introducing a phenylene (PTn-Ph) or vinylene phenylene (PTn-Vi-Ph) moiety in a meta configuration or when there is a large energy mismatch between the dye frontier levels and the oxide conduction band, as is the case for oligothiophene-S,S-dioxides (with LUMO levels deep below the oxide CBE). Implications for electron injection into the titania and the optical absorption properties of the oxidedye hybrids are discussed.
First author: Fihey, A, Plasmon-Excitation Coupling for Dithienylethene/Gold Nanoparticle Hybridg Systems: A Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 9995, (2015)
Abstract: We present a theoretical study dedicated to the optical response properties of a photochromic dithienylethene molecule physisorbed on gold nanoparticles (NPs). The absorption spectra are obtained with the discrete interaction model/quantum mechanics scheme recently developed by Jensen and coworkers. This hybrid scheme relies on an atomistic electrodynamics model of the metal NP and a time-dependent density functional theory description of the molecule. The first two absorption bands, S-1 and S-2, of the closed-ring dithienylethene, overlap with the plasmon resonance band of the metallic part. These bands are found to be highly impacted by the localized enhanced electric field generated by the external field applied (the plasmon band) and, to a lesser extent, by the dipolar environment created by the gold atoms. The coupling between the molecular excitations and the plasmon is observed up to distances of the order of the NP diameter. This coupling is highly dependent on the orientation of the molecule with respect to the surface and on the adsorption site. These findings can actually be rationalized by the orientation of the transition dipole moment of S-1 and S-2 electronic excitations. A fine-tuning of the molecular position on top of the NP can thus enhance the intensity of the electronic excitation involved in the photochromic reaction.
First author: Pastore, M, First-Principles Modeling of a Dye-Sensitized TiO2/IrO2 Photoanode forg Water Oxidation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 5798, (2015)
Abstract: We present a first-principle computational modeling investigation, based on density functional theory (DFT) and time-dependent DFT, on the structural, electronic, optical, and charge generation properties of the semiconductor/dye/catalyst heterointerfaces in a prototypical dye-sensitized photoanode for water oxidation. The investigated architecture comprises a Ru(II) dye-sensitized TiO2 substrate tethered to an IrO2 nanoparticle catalyst. Our realistic modeling strategy and quantitative analysis of the relevant interfacial hole/electron transfer reactions indicates the slow hole injection into IrO2 and the fast dye excited-state quenching to IrO2 as the primary sources of the relatively poor cell efficiency experimentally observed. On the basis of this atomistic and electronic structure information, we propose and computationally test, against a prototype dye, a new class of Ru(II) sensitizers, which show potentially improved photoelectrochemical performances. This study constitutes a first step toward the computer-assisted design of new and more efficient materials for solar fuels production through dye-sensitized photoelectrochemical cells.
First author: Dillen, J, The Topology of the Ehrenfest Force Density Revisited. A Differentg Perspective Based On Slater-Type Orbitals, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 883, (2015)
Abstract: The topology of the Ehrenfest force density was studied with Slater-type orbitals (STO). At larger distances from the nuclei, STOs generate similar artefacts as noticed before with Gaussian-type orbitals. The topology of the Ehrenfest force density was found to be mainly homeomorphic with the topology of the electron density. For the first time, reliable integrations of several properties over force density atomic basins were performed successfully. Integration of the electron density of a number of hydrides, fluorides, and chlorides of first row elements over force density basins indicate substantial differences between the partial charges of the atoms as compared with those obtained from electron density basins. Calculations on saturated hydrocarbons confirm that the electronegativity of carbon atoms increases with increasing geometrical strain. Atomic interaction lines are observed to exist in the Ehrenfest force density between the hydrogen atoms of several so-called congested molecules, and also in some inclusion complexes of alkanes with helium. However, interaction lines are lacking in several other controversial cases.
First author: Kolesnikov, VI, Properties of Puma and Buksol lubricants modified by inorganic additivesg of binary polyphosphates, JOURNAL OF FRICTION AND WEAR, 36, 205, (2015)
Abstract: Results of investigations of tribotechnical and physicochemical properties of plastic lubricants, which are based on Puma and Buksol and used in heavy duty friction units of railway equipment, are presented. The search for new multipurpose polymeric additives of the inorganic nature was carried out based on physicochemical studies of phase diagrams of multicomponent systems. The influence of Puma and Buksol with the synthesized additives on characteristics of the process of friction is studied. Judgments about the mechanism of antifrictional and antiwear effect during work with these greases are stated. The base of this mechanism is the interaction of flexible links of anions of polyphosphate chains with a surface of metal. As a result, the layer of secondary structures is formed on the surface that protects the metal from wear.
First author: El Osta, R, Supramolecular Frameworks Built up from Red-Phosphorescent trans-Re-6g Cluster Building Blocks: One Pot Synthesis, Crystal Structures, and DFTg Investigations, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 641, 1156, (2015)
Abstract: The reaction of a K-4[{Re6S8i}(OH)(6)(a)]center dot 8H(2)O rhenium cluster salt with 4,4′-bipyridine (bpy) or 4-aminopyridine (apy) in an aqueous solution at mild temperature and pressure conditions lead to cluster functionalization and to the formation of two new compounds [{Re6S8i}(OH)(2)(a)(bpy)(4)(a)]center dot bpy center dot 4H(2)O (1) and [{Re6S8i}(OH)(2)(a)(apy)(4)(a)]center dot 2apy center dot 2H(2)O (2). Their crystal structures are built up from trans-[{Re6S8i}(OH)(2)(a)(L)(4)(a)] neutral units and the cohesions of both supramolecular frameworks are based on p-p stacking as well as hydrogen bonds, involving the cluster units trans[{Re6S8i}(OH)(2)(a)(L)(4)(a)], interstitial L ligands and water molecules. 1 and 2 present 2D and 3D cluster frameworks, respectively. Both compounds show red-NIR luminescence in the solid states. DFT calculations demonstrate that association of face capped Re-6 clusters with bpy and apy ligands enabled to form supramolecular frameworks that retain luminescent properties of the cluster units.
First author: Raju, M, Reactive Force Field Study of Li/C Systems for Electrical Energy Storage, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 2156, (2015)
Abstract: Graphitic carbon is still the most ubiquitously used anode material in Li-ion batteries. In spite of its ubiquity, there are few theoretical studies that fully capture the energetics and kinetics of Li in graphite and related nanostructures at experimentally relevant length, time-scales, and Li-ion concentrations. In this paper, we describe the development and application of a ReaxFF reactive force field to describe Li interactions in perfect and defective carbon-based materials using atomistic simulations. We develop force field parameters for Li-C systems using van der Waals-corrected density functional theory (DFT). Grand canonical Monte Carlo simulations of Li intercalation in perfect graphite with this new force field not only give a voltage profile in good agreement with known experimental and DFT results but also capture the in-plane Li ordering and interlayer separations for stage I and II compounds. In defective graphite, the ratio of Li/C (i.e., the capacitance increases and voltage shifts) both in proportion to the concentration of vacancy defects and metallic lithium is observed to explain the lithium plating seen in recent experiments. We also demonstrate the robustness of the force field by simulating model carbon nanostructures (i.e., both 0D and 1D structures) that can be potentially used as battery electrode materials. Whereas a 0D defective onion-like carbon facilitates fast charging/discharging rates by surface Li adsorption, a 1D defect-free carbon nanorod requires a critical density of Li for intercalation to occur at the edges. Our force field approach opens the opportunity for studying energetics and kinetics of perfect and defective Li/C structures containing thousands of atoms as a function of intercalation. This is a key step toward modeling of realistic carbon materials for energy applications.
First author: Groppo, E, XAS and XES Techniques Shed Light on the Dark Side of Ziegler-Nattag Catalysts: Active-Site Generation, CHEMCATCHEM, 7, 1432, (2015)
Abstract: The local structure and the electronic properties of the active Ti sites in heterogeneous Ziegler-Natta catalysts, generated insitu by interaction of the precatalyst with different Al-alkyl activators, were investigated by combining X-ray absorption and valence-to-core X-ray emission spectroscopy (XAS and vtc-XES), coupled with UV/Vis, FTIR, and DFT theoretical calculations. Irrespective of the activator used, the active system was found to be a highly dispersed TiCl3-like phase in which the Ti sites are surrounded, not only by bridged chlorine ligands (with the same bond length of bulk TiCl3), but also by terminal chlorine ligands, at a much shorter distance. These results set Ziegler-Natta catalysts in the category of complex nanomaterials. Despite the observation that the investigated catalysts polymerize ethylene, cutting-edge XAS and XES techniques do not yet offer unequivocal proof for the presence of any alkyl chain attached to the Ti sites, as a consequence of the small fraction of the active sites.
First author: Germer, W, Phase Separated Methylated Polybenzimidazole (O-PBI) Based Aniong Exchange Membranes, MACROMOLECULAR MATERIALS AND ENGINEERING, 300, 497, (2015)
Abstract: Methylated polybenzimidazole (O-PBI) based anion exchange membranes with a degree of methylation of ca. 78% were prepared in the iodide, chloride, carbonate, bicarbonate, and hydroxide form. Swelling in water showed a high anisotropy for chloride and carbonate exchangedmembranes and a strong plasticizing effect of water was confirmed by DMA. Carbonate and bicarbonate exchanged membranes revealed an ionomer peak around 0.25 angstrom(-1) in SAXS measurements suggesting a phase separated morphology. Theoretical DFT calculations were used to characterize geometries and electronic structure of polymer models and interactions with different anions, and to rationalize the water uptake/swelling behavior.
First author: Mansouri, L, Substitution effects and electronic properties of the azo dyeg (1-phenylazo-2-naphthol) species: a TD-DFT electronic spectrag investigation, CANADIAN JOURNAL OF CHEMISTRY, 93, 509, (2015)
Abstract: DFT/B3LYP and ab initio Hartree-Fock calculations with full geometry optimization have been carried out on hydrazo and azo forms of 1-phenylazo-2-naphthol and their substituted derivatives. The predicted geometries show that a small energy difference of 1.8 kcal/mol might tune the equilibrium between both forms. Depending on the electron donating and electron accepting of the different used substituents (CF3, NH2, CH3, Cl, and NO2), the various obtained isomers show small energy differencies between meta and para substitution except for the NH2 one, indicating the coexistence of the tautomers in solution. The ortho(C-12) position was found to be the less favored substitution in all cases, while the second ortho(C-16) position for different substituents provides isomers competing with the most stable meta and para ones. The obtained results suggest that a judicious choice in the substituents' use on the phenyl ring should lead to stabilization. The TD-DFT theoretical study performed on the optimized geometry allowed us to identify quite clearly the spectral position and the nature of the different electronic transitions according to their molecular orbital localization, hence, reproducing the available UV-Vis spectra. The increase in the wavelength values is in perfect agreement with red shifts and the Delta E (E-LUMO -E-HOMO) decreasing. Thus, from the point of view of both substitution and the used solvent, the obtained electronic spectra appear to behave quite differently.
First author: Mirzadeh, N, Formation of heterobinuclear Pt-Au complexes by chelate ring-opening ofg cis-[Pt(kappa(2)-C6R4PPh2)(2)] (R = H, F), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 783, 130, (2015)
Abstract: Mixed metal complexes of the type [Pt(kappa(2)-2-C6R4PPh2) (PPh3) (mu-2-C6R4PPh2)AuCl] (R = H, F) can be prepared by treatment of cis-[Pt(kappa(2)-C6R4PPh2)(2)] with [AuCl(PPh3)]. Under similar reaction conditions, the trans isomer of [Pt(kappa(2)-C6F4PPh2)(2)] is unreactive. Computational studies have been performed to provide insights into the reasons for this difference in reactivity. Density Functional Theory (DFT) calculations show that formation of an AuCl adduct of [Pt(kappa(2)-2-C6R4PPh2)(2)] is favoured over nucleophilic addition of PPh3 to Pt as the initial step of the reaction, and reveal the required energy of the cis and trans isomers of the bis-chelate [Pt(kappa(2)-2-C6R4PPh2)(2)] in forming the mixed metal Pt-Au compounds. NBO analysis sheds more light on the bonding orbitals of the cis and trans isomers, suggesting that the Pt-P bonds in the cis isomer are more labile.
First author: Li, P, Mechanistic aspects of the reaction of uranium atom with H2O in the gasg phase, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, 304, 489, (2015)
Abstract: The gas phase reaction of U atom with water molecule was investigated by means of the density functional theory calculations. Taking different possible spin states into account, a close description of the reaction mechanisms is presented. The nature of the chemical bonding evolution was investigated using diverse topological analyses including electron localization function and atoms in molecules.
First author: Petrie, S, Rationalising the Geometric Variation between the A and B Monomers ing the 1.9 angstrom Crystal Structure of Photosystem II, CHEMISTRY-A EUROPEAN JOURNAL, 21, 6780, (2015)
Abstract: Density functional theory calculations are reported on a set of models of the water-oxidising complex (WOC) of photosystem II (PSII), exploring structural features revealed in the most recent (1.9 angstrom resolution) X-ray crystallographic studies of PSII. Crucially, we find that the variation in the Mn-Mn distances seen between the A and B monomers of this crystal structure can be entirely accounted for, in the low oxidation state (LOS) paradigm, by consideration of the interplay between two hydrogen-bonding interactions involving proximate amino acid residues with the oxo bridges of the WOC, that is, His337 with O3 (which leads to a general elongation in the Mn-Mn distances between Mn1, Mn2 and Mn3) and Arg357 with O2 (which results in a specific elongation of the Mn2-Mn3 distance).
First author: Yao, SA, Electronic Structure of Ni2E2 Complexes (E = S, Se, Te) and a Globalg Analysis of M2E2 Compounds: A Case for Quantized E-2(n-) Oxidationg Levels with n=2, 3, or 4, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137, 4993, (2015)
Abstract: The diamagnetic compounds Cp'2Ni2E2 (1: E = S, 2: E = Se, 3: E = Te; Cp' = 1,2,3,4,-tetraisopropylcyclopentadienyl), first reported by Sitzmann and co-workers in 2001 [Sitzmann, H.; Saurenz, D.; Wolmershauser, G.; Klein, A.; Boese, R. Organometallics 2001, 20, 700], have unusual E center dot center dot center dot E distances, leading to ambiguities in how to best describe their electronic structure. Three limiting possibilities are considered: case A, in which the compounds contain singly bonded E-2(2)- units; case B, in which a three-electron E-E half-bond exists in a formal E-2(3-) unit; case C, in which two E-2(-) ions exist with no formal E-E bond. One-electron reduction of 1 and 2 yields the new compounds [Cp*Co-2][Cp'2Ni2E2] (1red: E = S, 2red: E = Se; Cp* = 1,2,3,4,5-pentamethylcyclopentadieyl). Evidence from X-ray crystallography, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy suggest that reduction of 1 and 2 is Ni-centered. Density functional theory (DFT) and ab initio multireference methods (CASSCF) have been used to investigate the electronic structures of 1-3 and indicate covalent bonding of an E23- ligand with a mixed-valent Ni-2(II,III) species. Thus, reduction of 1 and 2 yields Ni2(II,II) species 1red and 2red that bear unchanged E-2(3-) ligands. We provide strong computational and experimental evidence, including results from a large survey of data from the Cambridge Structural Database, indicating that M2E2 compounds occur in quantized E-2 oxidation states of (2 x E2-), E-2(3-), and E-2(2-), rather than displaying a continuum of variable E-E bonding interactions.
First author: Zheng, T, Probing the Influence of Phosphonate Bonding Modes to Uranium(VI) ong Structural Topology and Stability: A Complementary Experimental andg Computational Investigation, INORGANIC CHEMISTRY, 54, 3864, (2015)
Abstract: Systematic control of the reactions between U(VI) and 1,4-phenylenebis(methylene))bis(phosphonic acid) (pmbH(4)) allows for alterations in the bonding between these constituents and affords three uranyl phosphonate compounds with chiral one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) structures, namely, [TPA][UO2(pmbH(3))(pmbH(2))H2O]center dot 2H(2)O (1), [NH4](2)[UO2(pmb)] (2), UO2(pmbH(2)) (3), and the first uranyl mixed phosphite/phosphonate compound [TMA](2)[(UO2)2(pmb)(HPO3)] (4) (TPA = NPr4+, TMA = NMe4+). These compounds crystallize in the space groups P2(1)2(1)2(1), P (1) over bar, P2(1)/c, and Cmcm, respectively. Further investigation of the local uranyl coordination environment reveals that in 1 only oxygen atoms from P-O moieties ligate the uranium centers; whereas in 2 only P-O- oxygen atoms are involved in bonding and yield a layered topology. Compound 3 differs sharply from the first two in that conjugated P-O and P-O- oxygen atoms chelate the uranium centers resulting in a 3D framework. In compound 4, a phosphonate group bridges three uranyl centers further coordinated with a phosphite ligand HPO32-, which is a product of pmbH(4) decomposing, forming a 2D layered structure. Compounds 3 and 4 also contain a different coordination environment for U(VI) than that found in 1 or 2. In this case, tetragonal bipyramidal UO6 units occur instead of the far more common UO7 pentagonal bipyramids found in 1 and 2. Interestingly, 1 converts to 3 at elevated reaction temperatures, indicating that the formation of 1 is likely under kinetic control. This is supported by thermal analysis, which reveals that 3 has higher thermal stability than 1 or 2. UV-vis-near-IR absorption and fluorescence spectroscopy show that the absorption and photoluminescence intensity increases from 1 to 4. Density functional theory electronic structure calculations provide insight into the nature of the interactions between U(VI) and the phosphonate ligands.
First author: Hu, HX, A series of novel sandwich complexes: MQ(eta(4)-E-4)(2) (M = Be or Mg; Qg = C or Si; E = P, As, Sb or Bi) with donor-acceptor bonds, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1058, 41, (2015)
Abstract: A series of sandwich-like compounds MQ(eta(4)-E-4)(2) (M = Be or Mg; Q = Cot Si; E = P, As, Sb, or Bi) with centered donor acceptor bond Q M are investigated at the B3LYP/6-311+G(d)/SDD and M06-2x/6-311+G(d)/SDD levels of theory. The C-4v staggered conformations are predicted to be more stable than the eclipsed ones. Wiberg bond index, electron density and Laplacian of electron density were computed, which can provide an indication of the strength and the character of the bonds. The results indicate that the donor-acceptor Q-M bonds in these complexes (with Wiberg bond index values 0.153-0.203, small electron density values less than 0.1 au and positive Laplacian of electron density) are all ionic, and the C-Be bonds with relatively larger electron density are stronger than the Si Mg bonds. The bonds between M and E-4(2-) are ionic, whereas the Q-ligand bonds are covalent. The dissociation reactions show that these complexes are stable, and BeC(eta(4)-E-4)(2) with C-Be bond dissociation energies (DE) close to the Zn-Zn bond DE in the synthesized Zn-2(eta(5)-C5Me5)(2), may be synthesized in future experiments. Nucleus-independent chemical shift values suggest that the rings bonded to the donor atom have strong pi aromaticity.
First author: Huang, JD, Electronic Structure and Microscopic Charge-Transport Properties of ag New-Type Diketopyrrolopyrrole-Based Material, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 695, (2015)
Abstract: Recently, diketopyrrolopyrrole (DPP)-based materials have attracted much interest due to their promising performance as a subunit in organic field effect transistors. Using density functional theory and charge-transport models, we investigated the electronic structure and microscopic charge transport properties of the cyanated bithiophene-functionalized DPP molecule (compound 1). First, we analyzed in detail the partition of the total relaxation (polaron) energy into the contributions from each vibrational mode and the influence of bond-parameter variations on the local electron-vibration coupling of compound 1, which well explains the effects of different functional groups on internal reorganization energy (). Then, we investigated the structural and electronic properties of compound 1 in its isolated molecular state and in the solid state form, and further simulated the angular resolution anisotropic mobility for both electron- and hole-transport using two different simulation methods: (i) the mobility orientation function proposed in our previous studies (method 1); and (ii) the master equation approach (method 2). The calculated electron-transfer mobility (0.00003-0.784 cm(2) V-1 s(-1) from method 1 and 0.02-2.26 cm(2) V-1 s(-1) from method 2) matched reasonably with the experimentally reported value (0.07-0.55 cm(2) V-1 s(-1)). To the best of our knowledge, this is the first time that the transport parameters of compound 1 were calculated in the context of band model and hopping models, and both calculation results suggest that the intrinsic hole mobility is higher than the corresponding intrinsic electron mobility. Our calculation results here will be instructive to further explore the potential of other higher DPP-containing quinoidal small molecules.
First author: Romao, CP, Zero Thermal Expansion in ZrMgMo3O12: NMR Crystallography Revealsg Origins of Thermoelastic Properties, CHEMISTRY OF MATERIALS, 27, 2633, (2015)
Abstract: The coefficient of thermal expansion of ZrMgMo3O12 has been measured and was found to be extremely close to zero over a wide temperature range including room temperature ( = (1.6 ± 0.2) x 10(-7) K-1 from 25 to 450 degrees C by X-ray diffraction (XRD)). ZrMgMo3O12 belongs to the family of AMgM(3)O(12) materials, for which coefficients of thermal expansion have previously been reported to range from low-positive to low-negative. However, the low thermal expansion property had not previously been explained because atomic position information was not available for any members of this family of materials. We determined the structure of ZrMgMo3O12 by nuclear magnetic resonance (NMR) crystallography, using Zr-91, Mg-25, Mo-95, and O-17 magic angle spinning (MAS) and O-17 multiple quantum MAS (MQMAS) NMR in conjunction with XRD and density functional theory calculations. The resulting structure was of sufficient detail that the observed zero thermal expansion could be explained using quantitative measures of the properties of the coordination polyhedra. We also found that ZrMgMo3O12 shows significant ionic conductivity, a property that is also related to its structure.
First author: Zhugralin, AR, Experimental Gas-Phase and in Silico Investigation of beta-Methylg Elimination from Cationic Palladium Alkyl Species, ORGANOMETALLICS, 34, 1301, (2015)
Abstract: Herein we disclose experimental and in silico gas-phase studies of beta-methyl and beta-hydride elimination from cationic diphosphine palladium(II) neopentyl and isobutyl complexes. In particular, we have determined activation barriers for these transformations through mass-spectrometric threshold collision-induced dissociation (T-CID) studies. These systems can undergo at least one of the several competitive processes: (1) beta-methyl elimination, (2) Pd-C bond homolysis, or (3) beta-hydride elimination. We also confirm that qualitative trends in the branching ratios between these processes depend on the diphosphine bite angle, whereas electronic modifications of phosphine electron-donating ability have no significant effect on the barriers for beta-methyl elimination within the experimental error. The full reaction manifold has been investigated with density functional theory (DFT) and affords a valuable experimental benchmark for types of organometallic transformations described herein.
First author: Guidez, EB, Time-Dependent Density Functional Theory Study of the Luminescenceg Properties of Gold Phosphine Thiolate Complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 3337, (2015)
Abstract: The origin of the emission of the gold phosphine thiolate complex (TPA)AuSCH(CH3)(2) (TPA = 1,3,5-triaza-7-phosphaadamantanetriylphosphine) is investigated using time-dependent density functional theory (TDDFT). This system absorbs light at 3.6 eV, which corresponds mostly to a ligand-to-metal transition with some interligand character. The P-Au-S angle decreases upon relaxation in the S-1 and T-1 states. Our calculations show that these two states are strongly spin-orbit coupled at the ground state geometry. Ligand effects on the optical properties of this complex are also discussed by looking at the simple AuP(CH3)(3)SCH3 complex. The excitation energies differ by several tenths of an electronvolt Excited state optimizations show that the excited singlet and triplet of the (TPA)AuSCH(CH3)(2) complex are bent. On the other hand, the Au-S bond breaks in the excited state for the simple complex, and TDDFT is no longer an adequate method. The excited state energy landscape of gold phosphine thiolate systems is very complex, with several state crossings. This study also shows that the formation of the [(TPA)AuSCH(CH3)(2)](2) dimer is favorable in the ground state. The inclusion of dispersion interactions in the calculations affects the optimized geometries of both ground and excited states. Upon excitation, the formation of a Au-Au bond occurs, which results in an increase in energy of the low energy excited states in comparison to the monomer. The experimentally observed emission of the (TPA)AuSCH(CH3)(2) complex at 1.86 eV cannot be unambiguously assigned and may originate from several excited states.
First author: Gibson, JK, Infrared Multiphoton Dissociation Spectroscopy of a Gas-Phase Complex ofg Uranyl and 3-Oxa-Glutaramide: An Extreme Red-Shift of the [O=U=O](2+)g Asymmetric Stretch, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 3366, (2015)
Abstract: The gas-phase complex UO2(TMOGA)(2)(2+) (TMOGA = tetramethyl-3-oxa-glutaramide) prepared by electrospray ionization was characterized by infrared multiphoton dissociation (IRMPD) spectroscopy. The IRMPD spectrum from 700-1800 cm(-1) was interpreted using a computational study based on density functional theory. The predicted vibrational frequencies are in good agreement with the measured values, with an average deviation of only 8 cm(-1) (<1%) and a maximum deviation of 21 cm(-1) (<2%). The only IR peak assigned to the linear uranyl moiety was the asymmetric v(3) mode, which appeared at 965 cm(-1) and was predicted by DFT as 953 cm(-1). This v(3) frequency is red-shifted relative to bare uranyl, UO22+, by ca. 150 cm(-1) due to electron donation from the TMOGA ligands. Based on the degree of red-shifting, it is inferred that two TMOGA oxygen-donor ligands have a greater effective gas basicity than the four monodentate acetone ligands in UO2(acetone)(4)(2+). The uranyl v(3) frequency was also computed for uranyl coordinated by two TMGA ligands, in which the central O-ether, of TMOGA has been replaced by CH2. The computed v(3) for UO2(TMGA)(2)(2+), 950 cm(-1), is essentially the same as that for UO2(TMOGA)(2)(2+), suggesting that electron donation to uranyl from the ether of TMOGA is minor. The computed v(3) asymmetric stretching frequencies for the three actinyl complexes, UO2(TMOGA)(2)(2+), NpO2(TMOGA)(2)(2+) and PuO2(TMOGA)(2)(2+), are comparable. This similarity is discussed in the context of the relationship between v(3) and intrinsic actinide-oxygen bond energies in actinyl complexes.
First author: Chen, MY, Structures and Energetics of (MgCO3)(n) Clusters (n <= 16), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 3419, (2015)
Abstract: There is significant interest in the role of carbonate minerals for the storage of CO2 and the role of prenucleation dusters in their formation. Global minima for (MgCO3)(n) (n <= 16) structures were optimized using a tree growth-hybrid genetic algorithm in conjunction with MNDO/MNDO/d semiempirical molecular orbital calculations followed by density functional theory geometry optimizations with the B3LYP functional. The most stable isomers for (MgCO3)(n) (n < 5) are approximately 2-dimensional. Mg can be bonded to one or two 0 atoms of a CO32-, and the 1-O bonding scheme is more favored as the cluster becomes larger. The average C-Mg coordination number increases as the cluster size increases, and at n = 16, the average C-Mg coordination number was calculated to be 5.2. The normalized dissociation energy to form monomers increases as n increases. At n = 16, the normalized dissociation energy is calculated to be 116.2 kcal/mol, as compared to the bulk value of 153.9 kcal/mol. The adiabatic reaction energies for the recombination reactions of (MgO)(n) clusters and CO2 to form (MgCO3)(n) were calculated. The exothermicity of the normalized recombination energy < RE >(CO2) decreases as n increases and converged to the experimental bulk limit rapidly. The normalized recombination energy < RE >(CO2) was calculated to be -52.2 kcal/mol for the monomer and -30.7 kcal/mol for n = 16, as compared to the experimental value of -27.9 kcal/mol for the solid phase reaction. Infrared spectra for the lowest energy isomers were calculated, and absorption bands in the previous experimental infrared studies were assigned with our density functional theory predictions. The C-13, O-17, and Mg-25 NMR chemical shifts for the clusters were predicted. The results provide insights into the structural and energetic transitions from nanoclusters of (MgCO3)(n) to the bulk and the spectroscopic properties of clusters for their experimental identification.
First author: Robinson, TP, Synthesis of Anionic Phosphorus-Containing Heterocycles byg Intramolecular Cyclizations Involving N-Functionalizedg Phosphinecarboxamides, CHEMISTRY-A EUROPEAN JOURNAL, 21, 5727, (2015)
Abstract: We report that the 2-phosphaethynolate anion (PCO-) reacts with propargylamines in the presence of a proton source to afford novel N-derivatized phosphine-carboxamides bearing alkyne functionalities. Deprotonation of these species gives rise to novel five-and six-membered anionic heterocycles resulting from intramolecular nucleophilic attack of the resulting phosphide at the alkyne functionality (via 5-exo-dig or 6-endo-dig cyclizations, respectively). The nature of the substituents on the phosphinecarboxamide can be used to influence the outcome of these reactions. This strategy represents a unique approach to phosphorus-containing heterocylic systems that are closely related to known organic molecules with interesting bio-active properties.
First author: McKemmish, LK, Efficient calculation of integrals in mixed ramp-Gaussian basis sets, JOURNAL OF CHEMICAL PHYSICS, 142, 5727, (2015)
Abstract: Algorithms for the efficient calculation of two-electron integrals in the newly developed mixed ramp-Gaussian basis sets are presented, alongside a Fortran90 implementation of these algorithms, RAMPITUP. These new basis sets have significant potential to (1) give some speed-up (estimated at up to 20% for large molecules in fully optimised code) to general-purpose Hartree-Fock (HF) and density functional theory quantum chemistry calculations, replacing all-Gaussian basis sets, and (2) give very large speed-ups for calculations of core-dependent properties, such as electron density at the nucleus, NMR parameters, relativistic corrections, and total energies, replacing the current use of Slater basis functions or very large specialised all-Gaussian basis sets for these purposes. This initial implementation already demonstrates roughly 10% speed-ups in HF/R-31G calculations compared to HF/6-31G calculations for large linear molecules, demonstrating the promise of this methodology, particularly for the second application. As well as the reduction in the total primitive number in R-31G compared to 6-31G, this timing advantage can be attributed to the significant reduction in the number of mathematically complex intermediate integrals after modelling each ramp-Gaussian basis-function-pair as a sum of ramps on a single atomic centre.
First author: Su, J, Photoelectron spectroscopy and theoretical studies of gaseous uraniumg hexachlorides in different oxidation states: UCl6q- (q=0-2), JOURNAL OF CHEMICAL PHYSICS, 142, 5727, (2015)
Abstract: Uranium chlorides are important in actinide chemistry and nuclear industries, but their chemical bonding and many physical and chemical properties are not well understood yet. Here, we report the first experimental observation of two gaseous uranium hexachloride anions, UCl6- and UCl62-, which are probed by photoelectron spectroscopy in conjunction with quantum chemistry calculations. The electron affinity of UCl6 is measured for the first time as +5.3 eV; its second electron affinity is measured to be +0.60 eV from the photoelectron spectra of UCl62-. We observe that the detachment cross sections of the 5f electrons are extremely weak in the visible and UV energy ranges. It is found that the one-electron one-determinental molecular orbital picture and Koopmans' theorem break down for the strongly internally correlated U-5f(2) valence shell of tetravalent U+4 in UCl62-. The calculated adiabatic and vertical electron detachment energies from ab initio calculations agree well with the experimental observations. Electronic structure and chemical bonding in the uranium hexachloride species UCl62- to UCl6 are discussed as a function of the oxidation state of U.
First author: Reineke, MH, Synthesis and Structural Studies of Nickel(0) Tetracarbene Complexesg with the Introduction of a New Four-Coordinate Geometric Index,g tau(delta), INORGANIC CHEMISTRY, 54, 3211, (2015)
Abstract: The synthesis and characterization of two homoleptic chelating nickel(0) tetracarbene complexes are reported. These are the first group 10 M(0) (M = Ni, Pd, Pt) tetracarbene complexes. These species have geometries intermediate between C-2v sawhorse and tetrahedral and show high UV-vis absorption in the 350-600 nm range, with extinction coefficients (epsilon) between 5600 and 9400 M-1 cm(-1). Density functional theory analysis indicates that this high absorptivity is due to metal-to-ligand charge transfer. In order to better describe the unusual geometries encountered in these complexes, an adjustment to the popular tau(4) index for four-coordinate geometries is introduced in order to better delineate between sawhorse and distorted tetrahedral geometries.
First author: Thornley, WA, Photochemistry of the Permanganate Ion in Low-Temperature Frozeng Matrices, INORGANIC CHEMISTRY, 54, 3370, (2015)
Abstract: Photolysis of the permanganate anion, MnO4-, in tetralkylammonium tetrafluoroborate matrices at 85 K results in formation of a single product, the metastable manganese(V) peroxo complex MnO2(eta(2)-O-2)(-). Although previously unobserved, this peroxo species has been postulated to be an intermediate in the photodecomposition of permanganate, yielding O-2 and MnO2. Results from variable-temperature and intensity-dependence photolysis experiments in solution, however, suggest that MnO2(eta(2)-O-2)(-) does not lose O-2 thermally or photochemically and is not an intermediate in the photodecomposition reaction. A mechanism is proposed in which MnO2(eta(2)-O-2)(-) is formed through vibrational relaxation of an excited [MnO4-]* species, which may also follow an alternative relaxation pathway that results in the formation of MnO2- and O-2(-) photodecomposition products.
First author: Zalis, S, Spin-Orbit TDDFT Electronic Structure of Diplatinum(II,II) Complexes, INORGANIC CHEMISTRY, 54, 3491, (2015)
Abstract: [Pt-2(mu-P2O5H2)(4)](4) (Pt(pop)) and its perfluoroborated derivative [Pt-2(mu-P2O5(BF2)(2))(4)](4) (Pt(pop-BF2)) are d(8)-d(8) complexes whose electronic excited states can drive reductions and oxidations of relatively inert substrates. We performed spinorbit (SO) TDDFT calculations on these complexes that account for their absorption spectra across the entire UV-vis spectral region. The complexes exhibit both fluorescence and phosphorescence attributable, respectively, to singlet and triplet excited states of ds*ps origin. These features are energetically isolated from each other (similar to 7000 cm(-1) for (Pt(pop-BF2)) as well as from higher-lying states (5800 cm(-1)). The lowest (3)d sigma*p sigma state is split into three SO states by interactions with higher-lying singlet states with dpps and, to a lesser extent, ppps contributions. The spectroscopically allowed d sigma*p sigma SO state has similar to 96% singlet character with small admixtures of higher triplets of partial dpps and ppps characters that also mix with (3)d sigma*p sigma, resulting in a second-order (1)d sigma*p sigma-(3)d sigma*p sigma SO interaction that facilitates intersystem crossing (ISC). All SO interactions involving the ds*ps states are weak because of large energy gaps to higher interacting states. The spectroscopically allowed d sigma*p sigma SO state is followed by a dense manifold of ligand-to-metalmetal charge transfer states, some with ppps (at lower energies) or dpps contributions (at higher energies). Spectroscopically active higher states are strongly spin-mixed. The electronic structure, state ordering, and relative energies are minimally perturbed when the calculation is performed at the optimized geometries of the (1)d sigma*p sigma and (3)d sigma*p sigma excited states (rather than the ground state). Results obtained for Pt(pop) are very similar, showing slightly smaller energy gaps and, possibly, an additional (1)d sigma*p sigma (3)d sigma*p sigma second order SO interaction involving higher (1)d pi p sigma* states that could account in part for the much faster ISC. It also appears that (1)d sigma*p sigma -> (3)d sigma*p sigma ISC requires a structural distortion that has a lower barrier for Pt(pop) than for the more rigid Pt(pop-BF2).
First author: Cao, GJ, An 18-Electron System Containing a Superheavy Element: Theoreticalg Studies of Sg@Au-12, INORGANIC CHEMISTRY, 54, 3695, (2015)
Abstract: M@Au-12 cage molecules (M = transition element from group 6) are interesting clusters with high-symmetric structure and significant stability. As the heavier homologue of W is (106)Sg, it is interesting to pinpoint whether the Sg@Au-12 cluster is also stable. Geometric and electronic structures and bonding of various Sg@Au-12 isomers were investigated with density functional theory (PW91, PBE, B3LYP) and wave function theory (MP2, CCSD(T)) approaches. The lowest-energy isomer of Sg@Au-12 has icosahedral symmetry with significant Sg(6d)-Au(6s) covalent-metallic interaction and is comparable to the lighter homologues (M = Mo, W), with similar binding energy, although Sg follows (as a rare case) the textbook rule ns below (n – 1)d. The 12 6s valence electrons from Au-12 and the six 7s6d ones from Sg can be viewed as an 18e system below and above the interacting Au 5d band, forming nine delocalized multicenter bond pairs with a high stability of similar to 0.8 eV of bond energy per each of the 12 SgAu contacts. Different prescriptions (orbital, multipole-deformation, charge-partition, and X-ray-spectroscopy based ones) assign ambiguous atomic charges to the centric and peripheral atoms; atomic core-level energy shifts correspond to some negative charge shift to the gold periphery, more so for Cr@Au-12 than for Sg@Au-12 or Au@Au-12.
First author: Trnka, T, Stepwise Catalytic Mechanism via Short-Lived Intermediate Inferred fromg Combined QM/MM MERP and PES Calculations on Retainingg Glycosyltransferase ppGalNAcT2, PLOS COMPUTATIONAL BIOLOGY, 11, 3695, (2015)
Abstract: The glycosylation of cell surface proteins plays a crucial role in a multitude of biological processes, such as cell adhesion and recognition. To understand the process of protein glycosylation, the reaction mechanisms of the participating enzymes need to be known. However, the reaction mechanism of retaining glycosyltransferases has not yet been sufficiently explained. Here we investigated the catalytic mechanism of human isoform 2 of the retaining glycosyltransferase polypeptide UDP-GalNAc transferase by coupling two different QM/MM-based approaches, namely a potential energy surface scan in two distance difference dimensions and a minimum energy reaction path optimisation using the Nudged Elastic Band method. Potential energy scan studies often suffer from inadequate sampling of reactive processes due to a predefined scan coordinate system. At the same time, path optimisation methods enable the sampling of a virtually unlimited number of dimensions, but their results cannot be unambiguously interpreted without knowledge of the potential energy surface. By combining these methods, we have been able to eliminate the most significant sources of potential errors inherent to each of these approaches. The structural model is based on the crystal structure of human isoform 2. In the QM/MM method, the QM region consists of 275 atoms, the remaining 5776 atoms were in the MM region. We found that ppGalNAcT2 catalyzes a same-face nucleophilic substitution with internal return (SNi). The optimized transition state for the reaction is 13.8 kcal/mol higher in energy than the reactant while the energy of the product complex is 6.7 kcal/mol lower. During the process of nucleophilic attack, a proton is synchronously transferred to the leaving phosphate. The presence of a short-lived metastable oxocarbenium intermediate is likely, as indicated by the reaction energy profiles obtained using high-level density functionals.
First author: Vicha, J, Understanding the Electronic Factors Responsible for Ligand Spin-Orbitg NMR Shielding in Transition-Metal Complexes, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 1509, (2015)
Abstract: The significant role of relativistic effects in altering the NMR chemical shifts of light nuclei in heavy-element compounds has been recognized for a long time; however, full understanding of this phenomenon in relation to the electronic structure has not been achieved. In this study, the recently observed qualitative differences between the platinum and gold compounds in the magnitude and the sign of spin-orbit-induced (SO) nuclear magnetic shielding at the vicinal light atom (C-13, N-15), sigma SO(LA), are explained by the contractions of 6s and 6p atomic orbitals in Au complexes, originating in the larger Au nuclear charge and stronger scalar relativistic effects in gold complexes. This leads to the chemical activation of metal 6s and 6p atomic orbitals in Au complexes and their larger participation in bonding with the ligand, which modulates the propagation of metal-induced SO effects on the NMR signal of the LA via the Spin-Orbit/Fermi Contact (SO/FC) mechanism. The magnitude of the sSO(LA) in these square-planar complexes can be understood on the basis of a balance between various metal-based 5d -> 5d* and 6p -> 6p* orbital magnetic couplings. The large and positive sSO(LA) in platinum complexes is dominated by the shielding platinum-based 5d -> 5d* magnetic couplings, whereas small or negative sigma(SO)(LA) in gold complexes is related to the deshielding contribution of the gold-based 6p -> 6p* magnetic couplings. Further, it is demonstrated that sigma(SO)(LA) correlates quantitatively with the extent of M-LA electron sharing that is the covalence of the M-LA bond (characterized by the QTAIM delocalization index, DI). The present findings will contribute to further understanding of the origin and propagation of the relativistic effects influencing the experimental NMR parameters in heavy-element systems.
First author: Thornley, WA, Evidence for Photochemical Linkage Isomerism of the Phenylazo Ligand ing M(CO)(2)(N2Ph)(PPh3)(2) Cations (M = Fe and Ru), EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 11, 1946, (2015)
Abstract: Frozen-matrix photolysis studies of M(CO)(2)(N2Ph)(PPh3)(2) cations (M = Fe and Ru) have revealed end-on/side-on photochemical linkage isomerism of the phenylazo ligand. The previously reported solvent-dependent vibrational bands of the Ru(CO)(2)(N2Ph)(PPh3)(2) cation have now been identified as an equilibrium between the two linkage isomers. DFT calculations have been performed on the end-on and side-on isomers of the iron and ruthenium complexes.
First author: Hamieh, A, Well-Defined Surface Species [( Si-O)W(=O)Me-3) Prepared by Directg Methylation of [( Si-O-)W(=O)Cl-3), a Catalyst for Cycloalkaneg Metathesis and Transformation of Ethylene to Propylene, ACS CATALYSIS, 5, 2164, (2015)
Abstract: The silica-supported tungsten oxo-trimethyl complex [( Si-O-)W(= O)Me-3] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl4 on the surface of silica, partially dehydroxylated at 700 degrees C (SiO2-700), a well-defined monopodal surface complex [( Si-O-)W(= O)Cl-3] was produced. The supported complex directly methylated with ZnMe2 and transformed into [( Si-O-)W(= O)Me-3], which we fully characterized by microanalysis, IR, mass balance and SS NMR (H-1, C-13, H-1-C-13 HETCOR, H-1-H-1 DQ and TQ). [( Si-O)W(= O)Me-3] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature C-13 CP/MAS and H-1 spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [( Si-O)W(= O)Me-3] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [( Si-O)W(= O)Me-3] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes.
First author: Wang, YX, Theoretical investigation of the mechanism of ethylene polymerizationg with salicylaldiminato vanadium(III) complexes, CHINESE JOURNAL OF CATALYSIS, 36, 657, (2015)
Abstract: The use of vanadium-based catalysts allows the preparation of high molecular mass polymers with uniform molecular mass distributions, polypropylene and ethylene/alpha-olefin copolymers with high a-olefin incorporation. However, the design of ligand systems with vanadium catalysts would face difficulties, because it is difficult to experimentally determine the structures of the active species of vanadium catalysts. In this paper, possible structural candidates for the active species in ethylene polymerization catalyzed by the salicylaldiminato vanadium complex combined with AlEt2Cl were investigated using density functional theory. By comparing theoretical simulation results with previous experimental investigations, especially regarding the crucial role of the diethyaluminum chloride (AlEt2Cl) cocatalyst, it was concluded that a neutral bimetallic species containing two Al-Cl-V bridging bonds is the most favorable structure model for the active vanadium species. A notable effect of Al co-catalysts was clarified in the theoretical investigation. During the formation of the active species, AlEt2Cl act as an assistant for the alkylation and alkyl abstract processes of precursors. More importantly, AlEt2Cl is necessary for the formation of the bis(chlorine-bridged) structure in the active species, which showed a notable effect on the structural stability of the active species and its catalytic activity. Additionally, we investigated the chain termination mechanism in this system.
First author: Fagiani, MR, Opening of an icosahedral boron framework: A combined infraredg spectroscopic and computational study, CHEMICAL PHYSICS LETTERS, 625, 48, (2015)
Abstract: The opening of an icosanderal boron cage in the periodinated closo-dodecaborate B12I122- upon deiodination is studied using cryogenic ion trap vibrational spectroscopy combined with electronic structure calculations. Comparison of simulated vibrational spectra to the infrared photodissociation spectra of messenger-tagged B12I122- and B12In- (n = 7-9) formed by skimmer collision induced dissociation shows that the larger clusters absorb exclusively below 975 cm(-1) and hence exhibit quasi-icosahedral B-12-cage structures, while the higher energy absorptions in-between 1000 and 1300 cm(-1) observed for n = 7 can only be recovered by considering a breakup of the icosahedral cage upon deiodination from n = 8 to n = 7.
First author: Deng, WQ, Quantitative prediction of charge mobilities of pi-stacked systems byg first-principles simulation, NATURE PROTOCOLS, 10, 632, (2015)
Abstract: This protocol is intended to provide chemists and physicists with a tool for predicting the charge carrier mobilities of pi-stacked systems such as organic semiconductors and the DNA double helix. An experimentally determined crystal structure is required as a starting point. The simulation involves the following operations: (i) searching the crystal structure; (ii) selecting molecular monomers and dimers from the crystal structure; (iii) using density function theory (DFT) calculations to determine electronic coupling for dimers; (iv) using DFT calculations to determine self-reorganization energy of monomers; and (v) using a numerical calculation to determine the charge carrier mobility. For a single crystal structure consisting of medium-sized molecules, this protocol can be completed in similar to 4 h. We have selected two case studies (a rubrene crystal and a DNA segment) as examples of how this procedure can be used.
First author: Cysewski, P, Pressure-imposed changes of benzoic acid crystals, JOURNAL OF MOLECULAR MODELING, 21, 632, (2015)
Abstract: Structural and energetic properties of benzoic acid crystals at pressure elevated from ambient condition up to 2.21 GPa were characterized. The directly observed variations of cell parameters and consequently cell volume are associated with many other changes including energetic, geometric, and electronic characteristics. First of all the non-monotonous change of lattice energy are noticed with the rise of pressure since the increase of stabilization up to 1GPa is followed by systematic decrease of lattice energies after extending the hydrostatic compression. There is also an observed increase of C-2(2)(8) synthon stabilization interaction with increase of pressure. The lattice response rather than interaction within synthons are source of observed pressure-related trend of lattice energy changes. The energy decomposition analysis revealed that the total steric interactions determine the overall trend of lattice energy change with the rise of pressure. Besides geometric aromaticity index was used as a measure of geometric changes. Serious discrepancies were noticed between HOMA values computed with the use of experimental and optimized geometries of the ring. Even inclusion of uncertainties of experimental geometries related to limited precision of X-ray diffraction measurements does not cancel mentioned discrepancies. Although HOMA exhibit similar trends at modest pressures the diversity became surprisingly high at more extreme conditions. This might suggest limitations of periodic DFT computations at elevated pressures and the experimentally observed breaking of molecules at very high pressures will probably not be accounted properly in this approach. Also limitation of direct use of experimental geometries were highlighted.
First author: Olvera-Neria, O, The N2O activation by Rh-5 clusters. A quantum chemistry study, JOURNAL OF MOLECULAR MODELING, 21, 632, (2015)
Abstract: Nitrous oxide (N2O) is a by-product of exhaust pipe gases treatment produced by motor vehicles. Therefore, the N2O reduction to N-2 is necessary to meet the actual environmental legislation. The N2O adsorption and dissociation assisted by the square-based pyramidal Rh-5 cluster was investigated using the density functional theory and the zero-order regular approximation (ZORA). The Rh-5 sextet ground state is the most active in N2O dissociation, though the quartet and octet states are also active because they are degenerate. The Rh-5 cluster spontaneously activates the N-2-O cleavage, and the reaction is highly exothermic ca. -75 kcal mol(-1). The N-2-O breaking is obtained for the geometrical arrangement that maximizes the overlap and electron transfers between the N2O and Rh-5 frontier orbitals. The Rh-5 high activity is due to the Rh 3d orbitals are located between the N2O HOMO and LUMO orbitals, which makes possible the interactions between them. In particular, theO 2p states strongly interact with Rh 3d orbitals, which finally weaken the N-2-O bond. The electron transfer is from the Rh-5 HOMO orbital to the N2O antibonding orbital.
First author: Rezabal, E, Estimating pi Binding Energy of N-Heterocyclic Carbenes: The Role ofg Polarization, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 564, (2015)
Abstract: In this work, the tuneability of the acceptor or donor properties of a set of N-heterocyclic carbenes (NHCs) with a wide spectrum of electronic characteristics is established by means of density functional theory and energy decomposition analysis (EDA) tools. Even though the main orbital interaction contribution to the NHC coordination is the sigma donation, a significant contribution of the interactions to the bond is observed. By means of carefully selected coordination sites, different contributions to the interactions could be identified and isolated. It includes not only the well known back donation and donation interactions, but also the intrafragment polarization, which has not been considered in previous studies. This can be obtained through the use of the extended transition state method for EDA combined with the natural orbitals for chemical valence and the constrained space orbital variation analysis. The contributions vary with the position of the heteroatoms and the presence of exocyclic substituents; the donation/backdonation interactions between NHC and the coordination site can range between 2 and 61% of the total orbital interactions, while the rest is owed to intrafragment polarization. Our results do not only contribute to the understanding of the electronic structure of NHC-based complexes, giving ways to improve their catalytic properties, but also provide comprehension on the modelization methods used to study their donor-acceptor interactions.
First author: de Oliveira, M, Solid-state EPR strategies for the structural characterization ofg paramagnetic NO adducts of frustrated Lewis pairs (FLPs), JOURNAL OF CHEMICAL PHYSICS, 142, 564, (2015)
Abstract: Anisotropic interactions present in three new nitroxide radicals prepared by N, N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and B-11, N-14, and P-31 hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to 14N and 31P, the ESEEM and HYSCORE spectra contain important information about the 11B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.
First author: Skara, G, Conceptual Quantum Chemical Analysis of Bonding and Noncovalentg Interactions in the Formation of Frustrated Lewis Pairs, CHEMISTRY-A EUROPEAN JOURNAL, 21, 5510, (2015)
Abstract: The contributions of covalent and noncovalent interactions to the formation of classical adducts of bulky Lewis acids and bases and frustrated Lewis pairs (FLPs) were scrutinized by using various conceptual quantum chemical techniques. Significantly negative complexation energies were calculated for fourteen investigated Lewis pairs containing bases and acids with substituents of various sizes. A Ziegler-Rauk-type energy decomposition analysis confirmed that two types of Lewis pairs can be distinguished on the basis of the nature of the primary interactions between reactants; dative-bond formation and concomitant charge transfer from the Lewis base to the acid is the dominant and most stabilizing factor in the formation of Lewis acid-base adducts, whereas weak interactions are the main thermodynamic driving force (> 50%) for FLPs. Moreover, the ease and extent of structural deformation of the monomers appears to be a key component in the formation of the former type of Lewis pairs. A Natural Orbital for Chemical Valence (NOCV) analysis, which was used to visualize and quantify the charge transfer between the base and the acid, clearly showed the importance and lack of this type of interaction for adducts and FLPs, respectively. The Noncovalent Interaction (NCI) method revealed several kinds of weak interactions between the acid and base components, such as dispersion, pi-pi stacking, C-H center dot center dot center dot pi interaction, weak hydrogen bonding, halogen bonding, and weak acid-base interactions, whereas the Quantum Theory of Atoms in Molecules (QTAIM) provided further conceptual insight into strong acid-base interactions.
First author: Chakraborty, D, In Quest of a Superhalogen Supported Covalent Bond Involving a Noble Gasg Atom, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 3064, (2015)
Abstract: The possibility of having neutral Xe-bound compounds mediated by some representative transition metal fluorides of general formula MX3 (where M=Ru, Os, Rh, Ir, Pd, Pt, Ag, Au and X=F) has been investigated through density functional theory based calculations. Nature of interaction between MX3 and Xe moieties has been characterized through detailed electron density, charge density and bond energy decomposition analyses. The feasibility of having compounds of general formula XeMX3 at 298 K has been predicted through thermodynamic considerations. The nature of interaction in between Xe and M atoms is partly covalent in nature and the orbital interaction is the dominant contributor toward these interactions as suggested by energy decomposition analysis.
First author: Borocci, S, Complexes of XeHXe+ with Simple Ligands: A Theoretical Investigation ong (XeHXe+) (L = N-2, CO, H2O, NH3), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 2383, (2015)
Abstract: The structure, stability, and harmonic frequencies of the (XeHXe+L-) complexes (L = N-2, CO, H2O, NH3) were investigated by ab initio and density functional theory (DFT) calculations. Their bonding situation was also assayed by natural bond orbital (NBO), atoms-in-molecules (AIM), and energy decomposition (EDA) analyses. For any L, we located a linear and a T-shaped isomer, whose energy difference progressively increases in the order N-2 < CO < H2O < NH3 and ranges from nearly 0 to 4.5 kcal mol(-1). The absolute complexation energies of both the linear and the T-shaped isomers also increase in the same order, and their EDA analysis revealed the prevailing contribution of electrostatic interactions. The noncovalent character of the bonding between XeHXe+ and L was confirmed by the AIM analysis. In particular, we based our investigation on the joint use of numerical AIM indices and graphic examination of the local Hamiltonian kinetic energy density, K(r). Interestingly, this function visually identifies the covalent regions occupied by XeHXe+ and L and the noncovalent zones existing between them, which include, in particular, the bond critical point located on the Xe-L bond paths. Only for the linear (XeHXe+)NH3 did the AIM analysis suggest an onset of covalency in the xenon-nitrogen interaction. Further work is in progress to examine the effectiveness of K(r), and its plotted forms, as a function of the bonding situation of noble-gas compounds.
First author: Makarewicz, E, Nature of the Bonding in the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I)g Molecules. Topological Study on Electron Density and the Electrong Localization Function (ELF), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 2401, (2015)
Abstract: Topological analysis of the electron localization function (ELF) has been carried out for the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I) molecules using the wave function approximated by the CCSD, MP2, and DFT(B3LYP, M062X) methods including zero-order regular approximation (ZORA). In the Ng-F bond, the bonding disynaptic attractor V(Ng,F) is missing; therefore, there are no signs of the covalent binding. The nature of the Au-Ng bond depends on the computational method used. Analysis of the ELF carried out for the AuArF and AuXeF molecules, with the wave function approximated by the CCSD and MP2 methods, shows the V(Au,Ng) attractor possibly corresponding to a partially covalent binding between the gold and noble gas atom. However, its very small basin population (<1e) and a very large value of the variance of the basin population suggest that the Au-Ng bond has a very delocalized character. Such bond nature may be related to the charge shift concept with a resonance of the Au(-+)NgX, Au(+-)NgX hybrids. The weakest Au-Ng bond, in terms of the smallest amount of electron density for the V(Au,Ng) basin, is found for the AuKrF molecule with the CCSD method (0.13e). The MP2 method, however, does not yield any V(Au, Ng) population; hence, the covalent Au-Kr bond is not confirmed. Because the V(Au,Ng) attractor is also not observed with the DFT method, the proper characterization of the Au-Ng bond requires proper description of correlation effects. Additional studies on the Au-2 and [AuXe](+) molecules, performed at the CCSD and B3LYP levels, exhibit no V(Au,Au) and V(Au,Xe) bonding basins either.
First author: Geboes, Y, Competition of C(sp(2)) X center dot center dot center dot O Halogeng Bonding and Lone Pair center dot center dot center dot pi Interactions:g Cryospectroscopic Study of the Complexes of C2F3X (X = F, Cl, Br, and I)g and Dimethyl Ether, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 2502, (2015)
Abstract: Inspection of the electrostatic potential of C2F3X (X = F, Cl, Br, and I) revealed a second electropositive region in the immediate vicinity of the C=C double bond apart from the sigma hole of chlorine, bromine, and iodine, leading to C(sp(2))-X center dot center dot center dot Y halogen bonding, through which complexes stabilized by so-called lone pair center dot center dot center dot pi interactions can be formed. Consequently, the experimental studies for the complexes of dimethyl ether with C2F3X (X = F, Cl, Br, and I) not only allowed one to experimentally characterize and rationalize the effects of hybridization on halogen bonding but, for the first time, also allowed the competition of C-X center dot center dot center dot Y halogen bonding and lone pair center dot center dot center dot pi interactions to be studied at thermodynamic equilibrium. Analysis of the infrared and Raman spectra reveals that in the cryosolutions of dimethyl ether and C2F3I, solely the halogen-bonded complex is present, whereas C2F3Br and C2F3Cl give rise to a lone pair center dot center dot center dot pi bonded complex as well as a halogen-bonded complex. Mixtures of dimethyl ether with C2F4 solely yield a lone pair center dot center dot center dot pi bonded complex. The experimentally derived complexation enthalpies for the halogen bonded complexes are found to be -14.2(5) kJ mol(-1) for C2F3I center dot DME and -9.3(5) kJ mol(-1) for C2F3Br center dot DME. For the complexes of C2F3Cl with dimethyl ether, no experimental complexation enthalpy could be obtained, whereas the C2F4 center dot DME complex has a complexation enthalpy of -5.5(3) kJ mol(-1). The observed trends have been rationalized with the aid of an interaction energy decomposition analysis (EDA) coupled to a Natural Orbital for Chemical Valence (NOCV) analysis and also using the noncovalent interaction index method.
First author: Zhang, QN, Experimental and Theoretical Studies of the Infrared Spectra and Bondingg Properties of NgBeCO(3) and a Comparison with NgBeO (Ng = He, Ne, Ar,g Kr, Xe), JOURNAL OF PHYSICAL CHEMISTRY A, 119, 2543, (2015)
Abstract: The novel neon complex NeBeCO3 has been prepared in a low-temperature neon matrix via codeposition of laser-evaporated beryllium atoms with O-2 + CO/Ne. Doping by the heavier noble gas atoms argon, krypton and xenon yielded the associated adducts NgBeCO(3) (Ng = Ar, Kr, Xe). The noble gas complexes have been identified via infrared spectroscopy. Quantum chemical calculations of NgBeCO(3) and NgBeO (Ng = He, Ne, Ar, Kr, Xe) using ab initio methods and density functional theory show that the Ng-BeCO3 bonds are slightly longer and weaker than the Ng-BeO bonds. The energy decomposition analysis of the Ng-Be bonds suggests that the attractive interactions come mainly from the Ng -> BeCO3 and Ng -> BeO sigma donation.
First author: Vanko, G, Detailed Characterization of a Nanosecond-Lived Excited State: X-ray andg Theoretical Investigation of the Quintet State in Photoexcitedg [Fe(terpy)(2)](2+), JOURNAL OF PHYSICAL CHEMISTRY C, 119, 5888, (2015)
Abstract: Theoretical predictions show that depending on the populations of the Fe 3d(xy), 3d(xz), and 3d(yz) orbitals two possible quintet states can exist for the high-spin state of the photoswitchable model system [Fe(terpy)(2)](2+). The differences in the structure and molecular properties of these B-5(2) and E-5 quintets are very small and pose a substantial challenge for experiments to resolve them. Yet for a better understanding of the physics of this system, which can lead to the design of novel molecules with enhanced photoswitching performance, it is vital to determine which high-spin state is reached in the transitions that follow the light excitation. The quintet state can be prepared with a short laser pulse and can be studied with cutting-edge time-resolved X-ray techniques. Here we report on the application of an extended set of X-ray spectroscopy and scattering techniques applied to investigate the quintet state of [Fe(terpy)(2)](2+) 80 ps after light excitation. High-quality X-ray absorption, nonresonant emission, and resonant emission spectra as well as X-ray diffuse scattering data clearly reflect the formation of the high-spin state of the [Fe(terpy)(2)](2+) molecule; moreover, extended X-ray absorption fine structure spectroscopy resolves the Fe-ligand bond-length variations with unprecedented bond-length accuracy in time-resolved experiments. With ab initio calculations we determine why, in contrast to most related systems, one configurational mode is insufficient for the description of the low-spin (LS)-high-spin (HS) transition. We identify the electronic structure origin of the differences between the two possible quintet modes, and finally, we unambiguously identify the formed quintet state as 5E, in agreement with our theoretical expectations.
First author: Sinha, I, A Highly Stabilizing Silver(I)-Mediated Base Pair in Parallel-Strandedg DNA, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 3603, (2015)
Abstract: The first parallel-stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag+ ion into an internal mispair to form a metal-mediated base pair has been created. Towards this end, the highly stabilizing 6FP-Ag+-6FP base pair comprising the artificial nucleobase 6-furylpurine (6 FP) was devised. A combination of temperature-dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal-mediated base pairs both by the Watson-Crick edge (i.e. in regular antiparallel-stranded DNA) and by the Hoogsteen edge (i.e. in parallel-stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6FP-Ag+-6FP base pair within parallel-stranded DNA is the most strongly stabilizing Ag+-mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 degrees C upon the binding of one Ag+ ion.
First author: Zurek, E, Theoretical Predictions of Novel Superconducting Phases of BaGe3 Stableg at Atmospheric and High Pressures, INORGANIC CHEMISTRY, 54, 2875, (2015)
Abstract: A series of new superconducting binary silicides and germanides have recently been synthesized under high-pressure high-temperature conditions. A representative member of this group, BaGe3, was theoretically investigated using evolutionary structure searches coupled with structural analogies in the pressure range from 1 atm to 250 GPa, where three new phases were discovered. At 1 atm, in addition to the synthesized P6(3)/mmc phase, we predicted two new phases, I4/mmm and Amm2, to be dynamically stable. The Amm2 structure comprises Ge clusters and triangular prisms intercalated with Ba and Ge atoms, a unique structural motif unknown to this group. The I4/mmm structure has been previously synthesized in binary silicides and is calculated to be thermodynamically stable in BaGe3 between 15.6 and 35.4 GPa. Above 35.4 GPa, two new phases of P (6) over bar m2 and R (6) over bar symmetry become the global minima and remain so up to the highest pressure considered. These two phases have very similar enthalpies, and both feature layers of double Kagome nets of Ge intercalated with Ba-Ge layers. The predicted phases are suggested to be metallic with itinerant electrons and to be potentially superconducting from the considerable electron-phonon coupling strength. Density functional perturbation calculations combined with the Allen-Dynes-modified McMillan formula were used to estimate the superconducting critical temperatures (T-c) for these new phases, which, with slight pressure variations, are comparable to the experimental T-c measured for the P6(3)/mmc phase.
First author: Lepetit, C, The Missing Entry in the Agostic-Anagostic Series: Rh(I)-eta(1)-Cg Interactions in P(CH)P Pincer Complexes, INORGANIC CHEMISTRY, 54, 2960, (2015)
Abstract: The missing entry, namely, the "C-anagostic" or eta(1)-C interaction, closing the agostic-anagostic series of metal-CH(aryl) interactions is found in a bis(amidiniophosphine) P(CH)P pincer rhodium complex. The three entries, namely, agostic eta(2)-(C,H), anagostic (related to hydrogen bonding, thus recoined here as "H-anagostic"), and C-anagostic interactions, are unambiguously characterized by electron localization function (ELF) topological analysis. Other theoretical tools Such as noncovalent interaction (NCI) analysis and Multicenter electron delocalization indices (MCIs) support the ELF characterization. A eta(2)-(C,H) agostic interaction is evidenced by a disynaptic V(C,H) or trisynaptic V(M,C,H) ELF basin with a significant quantum topological atoms in molecules (QTAIM) atomic contribution of the metal M and a large covariance (in absolute value) with the metal core basin C(M). The C-anagostic eta(1)-C interaction is Characterized by a disynaptic V(M,C) basin, a weak covariance (in absolute value) of V(C,H) and C(M) populations, and a negligible QTAIM atomic contribution of M to V(C,H). The relevance of these ELF signatures is evidenced in a selected series of related rhodium and osmium complexes.
First author: Miller, DP, Benzene derivatives adsorbed to the Ag(111) surface: Binding sites andg electronic structure, JOURNAL OF CHEMICAL PHYSICS, 142, 2960, (2015)
Abstract: Dispersion corrected Density Functional Theory calculations were employed to study the adsorption of benzenes derivatized with functional groups encompassing a large region of the activated/deactivated spectrum to the Ag(111) surface. Benzenes substituted with weak activating or deactivating groups, such as methyl and fluoro, do not have a strong preference for adsorbing to a particular site on the substrate, with the corrugations in the potential energy surface being similar to those of benzene. Strong activating(N(CH3)(2)) and deactivating (NO2) groups, on the other hand, possess a distinct site preference. The nitrogen in the former prefers to lie above a silver atom (top site), but in the latter a hollow hexagonal-closed-packed (H-hcp) site of the Ag(111) surface is favored instead. Benzenes derivatized with classic activating groups donate electron density from their highest occupied molecular orbital to the surface, and those functionalized with deactivating groups withdraw electron density from the surface into orbitals that are unoccupied in the gas phase. For benzenes functionalized with two substituents, the groups that are strongly activating or deactivating control the site preference and the other groups assume sites that are, to a large degree, dictated by their positions on the benzene ring. The relative stabilities of the ortho, meta, and para positional isomers of disubstituted benzenes can, in some cases, be modified by adsorption to the surface.
First author: Pahan, S, Density functional theoretical analysis of structure, bonding,g interaction and thermodynamic selectivity of hexavalent uranium (UO22+)g and tetravalent plutonium (Pu4+) ion complexes of tetramethylg diglycolamide (TMDGA),THEORETICAL CHEMISTRY ACCOUNTS, 134, 2960, (2015)
Abstract: In the well-known PUREX process, tertiary butyl phosphate shows preferential extraction of UO22+ over Pu4+, whereas tetraoctyl diglycolamide (TODGA) displays the reverse selectivity. The reversal of selectivity toward diglycolamide has been investigated here theoretically by considering shorter analogue of TODGA, tetramethyl diglycolamide (TMDGA). Structure, bonding, energetic parameter and thermodynamic parameters of UO22+ and Pu4+ ions with TMDGA in the gas and solvent phase have been reported in order to understand their complexation and extraction behavior. The calculation has been performed with generalized gradient approximated BP86 density functional and hybrid B3LYP functional employing SVP and TZVP basis set. The calculated structure obtained at BP86/SVP level of optimization is found to be in close agreement with the reported experimental data. The free energy of extraction, Delta G(ext), of UO22+ and Pu4+ ions from aqueous phase to the dodecane phase has been computed using the Born-Haber thermodynamic cycle in conjunction with COSMO (conductor like screening model) solvation approach. The free energy of extraction is predicted to be exergonic for explicit monomer water model. The free energy of extraction for Pu4+ ion is shown to be higher than that of UO22+ as observed in the reported solvent extraction experiment. Further, the suitability of non-polar solvents as organic diluents has been confirmed by the decreased free energy of extraction with increasing dielectric constant of the solvents. Natural population and orbital analysis indicate the electrostatic and small covalent nature of interactions between the metal ions and the tridentate TMDGA chelating ligand. The results presented here might be helpful in designing new ligands for efficient extraction of actinides.
First author: Perrin, ML, Single-Molecule Resonant Tunneling Diode, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 5697, (2015)
Abstract: Rectification has been at the foundation of molecular electronics. Most single-molecule diodes realized experimentally so far are based on asymmetries in the coupling with the electrodes or using the donor-acceptor principle. In general, however, their rectification ratios are usually small (<10). Here, we propose a single-molecule diode based on an orbital resonance while using the highest occupied molecular orbital (HOMO) and HOMO-1 as transport channels. Our proposed diode design is based on an asymmetric two-site model and analyzed with DFT + NEGF calculations. We find high rectification ratios, even in the case of symmetric coupling to the electrodes. In addition, we show that diode parameters such as the operating voltage and rectification ratio can be tuned by chemical design.
First author: Freitag, R, Electrochemical and Computational Chemistry Study ofg Mn(beta-diketonato)(3) complexes, ELECTROCHIMICA ACTA, 158, 418, (2015)
Abstract: Nine different Mn(beta-diketonato)(3) complexes, with beta-diketonato = dipivaloylmethanato, acetylacetonato, benzoylacetonato, dibenzoylmethanato, trifluoroacetylacetonato, trifluorothenoylacetonato, trifluorofuroylacetonato, trifluorobenzoylacetonato and hexafluoroacetylacetonato, were synthesized. The effect of the various substituents on the beta-diketonato backbone of these complexes, on the ease of oxidation and reduction of the central metal in the nine different Mn(beta-diketonato)(3) complexes, was studied by means of electrochemistry. It was found that, when adding aromatic substituents to the backbone of the beta-diketonato ligands of the complexes, the reduced/oxidized species were stabilized. It was also found that, when adding more electron withdrawing groups to the backbone of the beta-diketonato ligands of the complexes, that Mn(beta-diketonato)(3) complex was more easily reduced at a higher potential. Good linear relationships and trends were obtained between the mean value of peak oxidation and reduction potential of the Mn-III/Mn-II redox couple, and various electronic parameters and DFT calculated energies.
First author: Ashley, DC, How a Redox-Innocent Metal Promotes the Formal Reductive Elimination ofg Biphenyl Using Redox-Active Ligands, CHEMISTRY-A EUROPEAN JOURNAL, 21, 4308, (2015)
Abstract: One of the most compelling strategies for utilizing redox-active ligands is to perform redox events at the ligands to avoid accessing prohibitively high energy oxidation states at the metal center. This has been demonstrated experimentally in many systems, yet there is little understanding of the fundamental electronic structures involved with these transformations or how to control them. Here, the reductive elimination of biphenyl from [M(isq)(2)Ph-2] (M = Ti, Zr, and Hf and isq = 2,4-di-tert-butyl-6-tert-butyliminosemiquinone) was studied computationally. It was found that the metal remains in the + IV oxidation state and all redox chemistry was mediated by the redox-active ligands. Two types of electron-transfer mechanisms were identified, an asymmetric unpaired electron transfer (UET) and a symmetric pairwise electron transfer (PET), the former always being lower in energy. The energetic differences between these two mechanisms were explained through simple molecular orbital theory arguments. Despite the metal's redox-inactivity, it still has a marked influence on the calculated energetics of the reaction, with the Ti systems being much more reactive than the Zr/Hf systems. This primarily originates from the shorter Ti-Ph bond, which leads to a stronger filled-filled interaction between these ligands at the reactant state. This greater reactant destabilization leads to the lower activation energies.
First author: Choi, S, Accuracy of Lagrange-sinc functions as a basis set for electronicg structure calculations of atoms and molecules, JOURNAL OF CHEMICAL PHYSICS, 142, 4308, (2015)
Abstract: We developed a self-consistent field program based on Kohn-Sham density functional theory using Lagrange-sinc functions as a basis set and examined its numerical accuracy for atoms and molecules through comparison with the results of Gaussian basis sets. The result of the Kohn-Sham inversion formula from the Lagrange-sinc basis set manifests that the pseudopotential method is essential for cost-effective calculations. The Lagrange-sinc basis set shows faster convergence of the kinetic and correlation energies of benzene as its size increases than the finite difference method does, though both share the same uniform grid. Using a scaling factor smaller than or equal to 0.226 bohr and pseudopotentials with nonlinear core correction, its accuracy for the atomization energies of the G2-1 set is comparable to all-electron complete basis set limits (mean absolute deviation <= 1 kcal/mol). The same basis set also shows small mean absolute deviations in the ionization energies, electron affinities, and static polarizabilities of atoms in the G2-1 set. In particular, the Lagrange-sinc basis set shows high accuracy with rapid convergence in describing density or orbital changes by an external electric field. Moreover, the Lagrange-sinc basis set can readily improve its accuracy toward a complete basis set limit by simply decreasing the scaling factor regardless of systems.
First author: Skarmoutsos, I, Li+ Solvation in Pure, Binary, and Ternary Mixtures of Organic Carbonateg Electrolytes, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 4502, (2015)
Abstract: Classical molecular dynamics (MD) simulations and quantum chemical density functional theory (DFT) calculations have been employed in the present study to investigate the solvation of lithium cations in pure organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC)) and their binary (ECDMC, 1:1 molar composition) and ternary (EC-DMC-PC, 1:1:3 molar composition) mixtures. The results obtained by both methods indicate that the formation of complexes with four solvent molecules around Li+, exhibiting a strong local tetrahedral order, is the most favorable. However, the molecular dynamics simulations have revealed the existence of significant structural heterogeneities, extending up to a length scale which is more than five times the size of the first coordination shell radius. Due to these significant structural fluctuations in the bulk liquid phases, the use of larger size clusters in DFT calculations has been suggested. Contrary to the findings of the DFT calculations on small isolated clusters, the MD simulations have predicted a preference of Li+ to interact with DMC molecules within its first solvation shell and not with the highly polar EC and PC ones, in the binary and ternary mixtures. This behavior has been attributed to the local tetrahedral packing of the solvent molecules in the first solvation shell of Li+, which causes a cancellation of the individual molecular dipole vectors, and this effect seems to be more important in the cases where molecules of the same type are present. Due to these cancellation effects, the total dipole in the first solvation shell of Li+ increases when the local mole fraction of DMC is high.
First author: Murray, KA, Toward Functional Type III [Fe]-Hydrogenase Biomimics for H-2g Activation: Insights from Computation, CHEMISTRY-A EUROPEAN JOURNAL, 21, 3987, (2015)
Abstract: The chemistry of [Fe]-hydrogenase has attracted significant interest due to its ability to activate molecular hydrogen. The intriguing properties of this enzyme have prompted the synthesis of numerous small molecule mimics aimed at activating H-2. Despite considerable effort, a majority of these compounds remain nonfunctional for hydrogenation reactions. By using a recently synthesized model as an entry point, seven biomimetic complexes have been examined through DFT computations to probe the influence of ligand environment on the ability of a mimic to bind and split H-2. One mimic, featuring a bidentate diphosphine group incorporating an internal nitrogen base, was found to have particularly attractive energetics, prompting a study of the role played by the proton/hydride acceptor necessary to complete the catalytic cycle. Computations revealed an experimentally accessible energetic pathway involving a benzaldehyde proton/hydride acceptor and the most promising catalyst.
First author: Chatterjee, S, Electronic structures of hexane isomers studied using quantum mechanicsg and graph theory, JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY, 14, 3987, (2015)
Abstract: Electronic and topological properties of hexane (C6H14) and its five geometric isomers are systematically studied quantum mechanically using several techniques such as positron-electron annihilation gamma-ray spectra, C1s binding energy spectra and carbon nuclear magnetic resonance (NMR) spectra, as well as information derived from graph theory. It is revealed that the Doppler-shift in the gamma-ray spectra of the hexane isomers is in the vicinity of the n-hexane molecule with small structural dependency, in agreement with the fact that the measured Doppler-shifts of other linear alkanes are in the vicinity of hexane. The present study further reveals the electronic structures of hexane isomers, which are deeply rooted into the carbon core electrons, more than mere properties in the valence space. The calculations show that the highest occupied molecular orbitals (HOMOs) of the isomers exhibit less important roles in gamma-ray spectra; whereas the electron-positron annihilation is dominated by the electrons of the lowest occupied valence orbitals (LOVOs) and other valence electrons underneath the HOMO electrons, in agreement with previous findings. The present study further reveals that the C1s binding energies of the isomers exhibit association with the nodes of the isomers using graph theory. That is, more branched carbons likely engage with larger chemical shift, which is indicated by the largest eigenvalues (LEVs) of the adjacency matrix (AM) from graph theory. The chemical shift of the carbon NMR spectra is revealed by the LEVs of the Laplacian matrix (LM) obtained from chemical graph theory.
First author: Alvarado-Soto, L, Tryptophan-[Re6Se8I6](3-) Cluster Interaction: A Computational Study, JOURNAL OF CLUSTER SCIENCE, 26, 623, (2015)
Abstract: The interaction between tryptophan (Trp) and the [Re6Se8I6](3-) cluster is studied here using density functional theory calculations including relativistic scalar interactions via the zero-order regular approximation and solvent effects, which we describe in terms of interaction energies, Mulliken charge analysis and molecular orbitals. In the indole functional groups of the Trp-[Re6Se8I6](3-) cluster conjugates, modification of the molecular orbitals associated with Trp occurs because states associated with the [Re6Se8I6](3-) cluster and the hybrid orbitals have a mixed metal-molecule character, which is attributed to the stronger than expected pi interactions facilitated by the indole group in Trp. Here, we find that the energy transfer from hybrid states of Trp-[Re6Se8I6](3-) to clusters could reduce intrinsic fluorescence intensity of Trp in the conjugated system.
First author: Kelterer, AM, Rational design of long-wavelength absorbing and emitting carbostyrilsg aided by time-dependent density functional calculations, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1055, 25, (2015)
Abstract: We have used computational chemistry methods to aid the rational design of long-wavelength absorbing and emitting organic materials. For this purpose, the vertical electronic transition energies of 3,4-dicyano carbostyrils (quinolone-2(1H)-ones) substituted by electron-donating substituents (methoxy, methylamino, dimethylamino) at positions 6 and 7, are calculated by time-dependent density functional theory (B3LYP) within the Tamm-Dancoff approximation. Bulk solvent effects (DMSO, CH3CN, H2O) were taken into account by the CPCM salvation model. Particular long-wavelength absorptions (similar to 540 nm) are predicted for derivatives containing an amino group in position 6 irrespective of whether a 7-methoxy or a 7-amino group is present. In contrast, considerably shorter wavelength absorption (similar to 440 nm) can be expected for 6-methoxy-7-amino substituted 3,4-dicyano carbostyrils. Optimization of the first excited singlet state of 6-dimethylamino substituted carbostyrils leads to a perpendicular arrangement of the (CH3)(2)N-group with respect to the heterocyclic ring system accompanied by an extremely low electronic transition energy (1000-1500 nm) with vanishingly small intensity (oscillator strength f < 0.000). 6-methoxy-7-amino substituted carbostyrils are predicted to emit at 490-520 nm. An especially long-wavelength fluorescence (similar to 660 nm) is calculated for 6-amino-7-methoxy- as well as 6,7-bis (methylamino)-3,4-dicyanocarbostyril.
First author: Bistoni, G, Charge-displacement analysis via natural orbitals for chemical valence:g Charge transfer effects in coordination chemistry, JOURNAL OF CHEMICAL PHYSICS, 142, 25, (2015)
Abstract: We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism.
First author: Kaloni, TP, Structural and Electronic Properties of Pristine and Dopedg Polythiophene: Periodic versus Molecular Calculations, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 3979, (2015)
Abstract: Based on density functional theory calculations, the structural and electronic properties of polythiophene in periodic and oligomer forms have been investigated. In particular, the effects of Li or Cl adsorption onto a monolayer and Li or Cl intercalation into bulk or bilayer polythiophene are addressed using periodic calculations. The binding energy of Li or Cl adsorbed bulk or bilayer polythiophene is significantly larger than for the monolayer. The trends in the binding energy as a function of adsorbent remain the same for both the periodic and molecular cases. The band gap or HOMO-LUMO gap and charge transfer are analyzed. In addition, for the bulk or bilayer, different kinds of stacking have been considered. It is found that the parallel bulk or bilayer structure is energetically favorable compared to flipping the second layer by 180 degrees. This has been considered for both the periodic and oligomer forms. Moreover, for Li adsorption, polarons are found to be more stable than bipolarons, while the situation is opposite for Cl adsorption. The detailed analysis of the present study will be useful for understanding the structural properties and the tuneability of the electronic states, which is an important step to construct polythiophene-based electronic devices.
First author: Szatylowicz, H, Why 1,2-quinone derivatives are more stable than their 2,3-analogues?, THEORETICAL CHEMISTRY ACCOUNTS, 134, 3979, (2015)
Abstract: In this work, we have studied the relative stability of 1,2- and 2,3-quinones. While 1,2-quinones have a closed-shell singlet ground state, the ground state for the studied 2,3-isomers is open-shell singlet, except for 2,3-naphthaquinone that has a closed-shell singlet ground state. In all cases, 1,2-quinones are more stable than their 2,3-counterparts. We analyzed the reasons for the higher stability of the 1,2-isomers through energy decomposition analysis in the framework of Kohn-Sham molecular orbital theory. The results showed that we have to trace the origin of 1,2-quinones' enhanced stability to the more efficient bonding in the p-electron system due to more favorable overlap between the SOMO pi of the center dot C4n-2H2n-CH center dot center dot and center dot center dot CH-CO-CO center dot fragments in the 1,2-arrangement. Furthermore, whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric, energetic, and electronic), 2,3-quinone derivatives present a substantial breaking in monotonicity.
First author: Kovacs, A, Quantum Chemical Calculations and Experimental Investigations ofg Molecular Actinide Oxides, CHEMICAL REVIEWS, 115, 1725, (2015)
First author: Gutierrez-Sevillano, JJ, COSMO-3D: Incorporating Three-Dimensional Contact Information into theg COSMO-SAC Model, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 54, 2214, (2015)
Abstract: The COSMO-SAC model for the calculation of activity coefficients has been improved by incorporating three-dimensional geometric information on molecules. This information is added to the model by means of the effective contact area of the molecules. We define a procedure to compute this contact area by using a probing sphere. The probing sphere rolls around the COSMO surfaces of two contacting atoms to define a spherical cap on each atom. The segments of the COSMO surfaces within the spherical caps are marked, and the summation of their areas defines the contact area for a pair of contacting molecules. The effective contact areas are used to compute the sigma-profiles and the Onsager screening energies in the calculation of the surface activity coefficients, allowing us to remove one parameter from the COSMO-SAC model. The s-profiles and effective areas need to be calculated only once and can be stored in a database. We show that the new model, named COSMO-3D because some three-dimensional information (the position of surface segments and atom centers in 3D-space) is taken from the COSMO-output files, agrees better with experimental data than the COSMO-SAC implementation for nonpolar and polar mixtures, even though it uses one parameter less. We feel that the new concept of system-dependent effective contact area is a suitable starting point for the further improvement of COSMO-SAC.
First author: Frenking, G, No Need for a Re-examination of the Electrostatic Notation of theg Hydrogen Bonding: A Comment, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 2596, (2015)
First author: Send, R, Coupled-Cluster Studies of Extensive Green Fluorescent Protein Modelsg Using the Reduced Virtual Space Approach, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 2933, (2015)
Abstract: Accurate predictions of photoexcitation properties are a major challenge for modern methods of theoretical:chemistry. We show here how approximate coupled-cluster singles and doubles (CC2) calculations;, in combination with the reduced virtual space (RVS) approach can be employed in studies of excite states of large biomolecolar systems. The RVS-CC2 approach is used for accurately predicting optical properties of the p-hydroxyberizylidene-dihydroimidazolinone (p-HBDI) chromophore embedded in green fluorescent protein (GFP) models using quantum mechanical calculations in combination with large basis sets. We study the lowest excited states for the isolated and protein-embedded chromophore in two different protonation states, and show how omitting high-lying virtual orbitals in the RVS calculation of excitation energies renders large-scale CC2 studies computationally feasible. We-also discuss how-the error introduced by the RVS approach can be systematically estimated and controlled. The obtained CC2 excitation energies of 3.13-3.27 and 2.69-2.77 eV for the two protoriation states of different protein models are in excellent agreement with the maxima of the experimental absorption spectra of 3.12-3.14 and 2.61-2.64 eV, respectively. Thus, the calculated energy splitting between the excited States of the two protonation states is 0.44-0.52 eV, which agrees very well with the experimental value of 0.48-0.51 eV. The calculations at the RVS-CC2 level on the protein models show the importance of using large QM regions in studies of bioChromophores embedded in proteins.
First author: Georgiou, DC, The Fate of NHC-Stabilized Dicarbon, CHEMISTRY-A EUROPEAN JOURNAL, 21, 3377, (2015)
Abstract: The attempted synthesis of NHC-stabilized dicarbon (NHC=C=C=NHC) through deprotonation of a doubly protonated precursor ([NHC-CH=CH-NHC](2+)) is reported. Rather than deprotonation, a clean reduction to NHC=CH-CH=NHC is observed with a variety of bases. The apparent resistance towards deprotonation to the target compound led to a reinvestigation of the electronic structure of NHC -> C=C <- NHC, which showed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gap is likely too small to allow for isolation of this species. This is in contrast to the recent isolation of the cyclic alkylaminocarbene analogue (cAAC=C=C=cAAC), which has a large HOMO-LUMO gap. A detailed theoretical study illuminates the differences in electronic structures between these molecules, highlighting another case of the potential advantages of using cAAC rather than NHC as a ligand. The bonding analysis suggests that the dicarbon compounds are well represented in terms of donor-acceptor interactions L -> C-2 -> L (L=NHC, cAAC).
First author: Raimbault, N, Gauge-Invariant Calculation of Static and Dynamical Magnetic Propertiesg from the Current Density, PHYSICAL REVIEW LETTERS, 114, 3377, (2015)
Abstract: In this work we solve two problems related to the calculation of static and dynamical magnetic properties with ab initio theories. First, we show that the dependence of the dynamical magnetic dipole moment on the reference point of the multipole expansion and on the gauge origin of the vector potential have a clear physical significance. They are due to a dynamical electric dipole moment and an electric field, respectively. Both are fully determined by the experimental setup and do not pose any fundamental problem, contrary to what is commonly assumed. Second, in the static case, any dependence on the gauge origin is an artifact of the computational method. We show that the artificial dependence on the gauge origin can be removed in an elegant way by the introduction of a sum rule that puts the diamagnetic and paramagnetic contributions on equal footing. Our approach can be applied to calculate any magnetic observable that can be derived from the current density, and can be used in combination with any ab initio theory from which it can be obtained. To illustrate our method we apply it here to time-dependent current-density-functional theory for the calculation of static and dynamical magnetizabilities of molecules.
First author: Kumpulainen, T, Synthesis and Spectroscopic Characterization of 1,8-Naphthalimideg Derived "Super" Photoacids, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 2515, (2015)
Abstract: The ground- and excited-state acidbase properties of three novel naphthalimide-based super photoacids were studied using steady-state and time-resolved spectroscopy. The compounds exhibit pK(a) = 8.88.0 and pK(a)* = -1.2 to -1.9. The decrease in both ground- and excited-state pK(a) is achieved by attachment of an electron withdrawing group (sulfonate) on the aromatic system. All compounds are deprotonated upon excitation in alcohols and DMSO. Good correlation is established between the pK(a)* and the ratio of the neutral and anion emission intensities in a certain solvent. The excited-state intermolecular proton transfer to solvent (H2O and DMSO) is explained by a two-step model. In the first step, short-range proton transfer takes place, resulting in the formation of a contact ion pair. Free ion pairs are formed in the diffusion controlled second step.
First author: Zhang, X, Dynamic Jahn-Teller Effect in the Metastable High-Spin State of Solvatedg [Fe(terpy)(2)](2+), JOURNAL OF PHYSICAL CHEMISTRY C, 119, 3312, (2015)
Abstract: Characterizing structural distortions in the metastable spin states of d(4)d(7) transition metal ion complexes is crucial to understand the nature of their bistability and eventually control their switching dynamics. In particular, the impact of the JahnTeller effect needs to be assessed for any electronic configuration that could be effectively degenerate, as in e.g. the high-spin (HS) manifold of highly symmetric homoleptic FeII complexes. However, capturing its manifestations remains challenging since crystallization generally alters the molecular conformations and their interconversion. With the rapid progress of ultrafast X-ray absorption spectroscopy, it is now possible to collect data with unprecedented signal-to-noise ratio, opening up for detailed structural characterization of transient species in the homogeneous solution phase. By combining the analysis of picosecond X-ray absorption spectra with DFT simulations, the structure of the photoinduced HS state is elucidated for solvated [Fe(terpy)(2)](2+) (terpy = 2,2′:6′,2 "-terpyridine). This species can be viewed as the average 5B structure in D-2 symmetry that originates from a dynamic JahnTeller effect in the HS manifold. These results evidence the active role played by this particular instance of vibronic coupling in the formation of the HS state for this benchmark molecule. Ultimately, correlating the interplay between intramolecular and intermolecular degrees of freedom to conformational strain and distortions in real time should contribute to the development of advanced functionalities in transition metal ion complexes.
First author: Canton, SE, Mapping the Ultrafast Changes of Continuous Shape Measures ing Photoexcited Spin Crossover Complexes without Long-Range Order, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 3322, (2015)
Abstract: Establishing a tractable yet complete reaction coordinate for the spin-state interconversion in d(4)-d(7) transition metal complexes is an integral aspect of controlling the dynamics that govern their functionality. For spin crossover phenomena, the limitations of a single-mode approximation that solely accounts for an isotropic increase in the metal-ligand bond length have long been recognized for all but the simple octahedral monodentate FeII compounds. However, identifying the coupled deformations that also impact on the unimolecular rate constants remains experimentally and theoretically challenging, especially for samples that do not display long-range order or when crystallization profoundly alters the dynamics. Owing to the rapid progress in ultrafast X-ray absorption spectroscopy (XAS), it is now possible to obtain transient structural information in any physical phase with unprecedented details. Using picosecond XAS and DFT modeling, the structure adopted by the photoinduced high-spin state of solvated [Fe(terpy)(2)](2+) (terpy: 2,2′:6′,2 "-terpyridine) has been recently established. Based on these results, the methodology of the continuous shape measure is applied to classify and quantify the short-lived distortion of the first coordination shell. The reaction coordinate of the spin-state interconversion is clearly identified as a double axial bending. This finding sets a benchmark for gauging the influence of first-sphere and second-sphere interactions in the family of FeII complexes that incorporate terpy derivatives. Some implications for the optimization of related photoactive FeII complexes are also outlined.
First author: Dumont, E, Insights into the Structure of Intrastrand Cross-Link DNAg Lesion-Containing Oligonucleotides: G[8-5m]T and G[8-5]C from Molecularg Dynamics Simulations, BIOCHEMISTRY, 54, 1259, (2015)
Abstract: Oxidatively generated complex DNA lesions occur more rarely than single-nucleotide defects, yet they play an important role in carcinogenesis and aging diseases because they have proved to be more mutagenic than simple lesions. Whereas their formation pathways are rather well understood, the field suffers from the absence of structural data that are crucial for interpreting the lack of repair. No experimental structures are available for oligonucleotides featuring such a lesion. Hence, the detailed structural basis of such damaged duplexes has remained elusive. We propose the use of explicit solvent molecular dynamics simulations to build up damaged oligonucleotides containing two intrastrand cross-link defects, namely, the guanine-thymine and guanine-cytosine defects. Each of these lesions, G[8-5m]T and G[8-5]C, is placed in the middle of a dodecameric sequence, which undergoes an important structural rearrangement that we monitor and analyze. In both duplexes, the structural evolution is dictated by the more favorable stacking of guanine G6, which aims to restore p-stacking with the 3′ purine nucleobase. Subsequently, transient formation of hydrogen bonds with a strand shifting is observed. Our simulations are combined with density functional theory to rationalize the structural evolution. We report converging computational evidence that the G[8-5m]T- and G[8-5]C-containing stuctures evolve toward "abasic-like" duplexes, with a stabilization of the interstrand pairing noncovalent interactions. Meanwhile, both lesions restore B-helicity within tens of nanoseconds. The identification of plausible structures characterizes the last hydrogen abstraction step toward the formation of such defects as a non-innocent chemical reaction.
First author: Antipas, GSE, Quantum chemical calculations predict biological function: the case of Tg cell receptor interaction with a peptide/MHC class I, FRONTIERS IN CHEMISTRY, 3, 1259, (2015)
Abstract: A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide's electron spin density and intrinsically expressed by the protonation state of the peptide's N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.
First author: Thornley, WA, Photochemically Induced Intramolecular Six-Electron Reductiveg Elimination and Oxidative Addition of Nitric Oxide by theg Nitridoosmate(VIII) Anion, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54, 2068, (2015)
Abstract: UV photolysis of the nitridoosmate(VIII) anion, OsO3N , in low-temperature frozen matrices results in nitrogen-oxygen bond formation to give the Os-II nitrosyl complex OsO2(NO)(-) Photolysis of the Os-II nitrosyl product with visible wavelengths results in reversion to the parent Os-VIII complex. Formally a six-electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation. DFT modelling of this reaction proceeds through a step-wise mechanism taking place through a side-on nitroxyl Os-VI intermediate, OsO2(eta(2)-NO)(-).
First author: Reber, AC, Electronic structure, stability, and oxidation of boron-magnesiumg clusters and cluster solids, JOURNAL OF CHEMICAL PHYSICS, 142, 2068, (2015)
Abstract: Electronic structure studies on MgmBn- (1 <= n <= 15, 0 <= m <= 3) clusters have been performed to identify the nature of bonding and the origin of stability in the mixed clusters. Boron clusters are found to have planar structures marked by tangential, radial, and pi aromaticity. The maximum stability is achieved for when all three types of aromaticity are quenched. The ring like B-n(-) clusters are shown to be electron deficient for n = 6-8, and the addition of Mg atoms is found to enhance the stability of the boron cluster through ionic bonding that quenches the aromaticity and produces umbrella-like structures. Several species including MgB6-, MgB8-, Mg2B-, and Mg3B7- are found to have the largest Mg binding energies due to this mechanism. The transfer of a single electron from the Mg atom to the boron cluster results in a Mg atom with a half-filled 3s orbital that may serve as an ignition center for combustion. Studies on the MgB7 and MgB4 cluster solids indicate that they are constructed from icosahedral and umbrella-like motifs and are semiconductors with band gap energies of 1.46 eV and 0.41 eV, respectively.
First author: Barngrover, BM, Prediction of Nonradical Au(0)-Containing Precursors in Nanoparticleg Growth Processes, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 889, (2015)
Abstract: This density functional theory (DFT) investigation examines the formation of nonradical Au(0) species from the reduction of Au(I) species. The Au(I) complexes of interest are AuCl2-, AuBr2-, AuI2-, AuClPH3, and AuCl(H)SCH3(-), which are precursors for gold nanoparticle and cluster formation. Reaction of two of the Au(I) species with a hydride results in ejection of two of the ligands and formation of Au2 with two ligands still attached. AuX2- (where X = Cl, Br, or I) reactions eject two halides and form Au2X22-. AuClL(-) (where L = PH3, HSCH3, or SCH3-) reactions can eject either chloride, HCl, PH3, HSCH3, or SCH3- and form Au(0)L-2(q-) or Au(0)ClLq- (q = 0, 1, 2). The Au2Cl22- complex can further react with AuCl2-, which forms Au3Cl32- and a chloride anion. The new Au3Cl32- species can then react with AuCl2- or Au2Cl22- or with another Au3Cl32-. Larger clusters can be formed from these precursors. In this work, reactions in both methanol and benzene solvents are considered as models for one-phase and two-phase gold nanoparticle growth processes. Overall, this investigation shows how Au(0)-containing species can be formed without assuming the formation of Au(0) atoms (radical species).
First author: Wu, QY, Terminal U E (E = N, P, As, Sb, and Bi) Bonds in Uranium Complexes: Ag Theoretical Perspective, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 922, (2015)
Abstract: The compound L-U-N [L = [N(CH2CH2NSiPr(i)(3))(3)](3-), Pr(i) = CH(CH3)(2)] containing a terminal U-N triple bond has been synthesized and isolated successfully in experiments. To investigate the trend in the bonding nature of its pnictogen analogues, we have studied the L-U-E (E = N, P, As, Sb, and Bi) complexes using the scalar relativistic density functional theory. The terminal U-E multiple bond length increases in the order of U-N << U-P U-As < U-Sb < U-Bi, which can be supported by the hard and soft acids and bases (HSAB) theory. The U-E bond length, molecular orbital (MO), and natural bond orbital (NBO) reveal that the terminal U-E bonds should be genuine triple bonds containing one sigma- and two pi-bonding orbitals. Quantum theory of atoms in molecules (QTAIM) topological analysis and the electron localization function (ELF) suggest that the terminal U-E bond possesses covalent character and the covalency of U-E bonds decrease sharply when the terminal atom becomes heavier. This work presents a comparison about the bonding characteristic between the terminal U degrees N bond and its heavier pnictogen (P, As, Sb, and Bi) analogues. It is expected that this work would shed light on the evaluation of the amount of 5f orbital participation in multiple bonds and further facilitate our deeper understanding of f-block elements.
First author: Tao, JC, Hydrogen-release mechanisms in LiNH2BH3 center dot NH3BH3: A theoreticalg study, JOURNAL OF MOLECULAR STRUCTURE, 1081, 437, (2015)
Abstract: The molecular mechanism of the dehydrogenation of LiNH2BH3 center dot NH3BH3 to form [LiN2B2H] by the loss of five molar equiv of H-2 at two consecutive temperatures of 373 K and 501 K has been investigated using computational quantum chemistry methods (B3LYP, MP2 and CCSD(T) methods). The intermediate LiNHBH2 center dot NH2BH2 can be obtained through the pathway A at 373 K, in which LiH structures are formed by the transfer of hydridic H- from NH2BH3- to Li+ followed by the redox reactions of H delta+ and H delta- to form two molar equiv of H-2. The intermediate LiNH2BH=NHBH3 can also be generated via the pathway B at 373 K, in which a new N-B bond forms and two equiv of H-2 are released by the redox reactions. At 501 K, the predominant final product P-1 (LiNBNBH) is given most likely through the formation of LiH and a series of redox reactions with the loss of three molar equiv of H-2 in the pathway A Meanwhile, the products P-2 (LiNBBNH) and P-3 [Li( -NBBN-)H] may be also obtained by the dehydrogenation via a sequence of redox reactions of H delta+ and H delta- to release three equiv of H-2 at the temperature of 501 K. The present study would be helpful for experimental chemists to design better hydrogen-storage media.
First author: Chakraborty, D, Confinement induced binding in noble gas atoms within a BN-doped carbong nanotube, CHEMICAL PHYSICS LETTERS, 621, 29, (2015)
Abstract: Confinement induced binding interaction patterns for noble gas atoms (He-n/m, Ar-n, Kr-n; n=2, m=3) atoms inside pristine and -BN doped (3,3) single walled carbon nanotube (SWCNT) have been studied through density functional theory calculations. The kinetic stability for He dimer and trimer has been investigated at 100 K and 300 K through an ab initio molecular dynamics simulation. The positive role of doping in SWCNT in enhancing the nature of interaction as well as the kinetic stability of the said systems has been found.
First author: Duperrouzel, C, A quantum informational approach for dissecting chemical reactions, CHEMICAL PHYSICS LETTERS, 621, 160, (2015)
Abstract: We present a conceptionally different approach to dissect bond-formation processes in metal-driven catalysis using concepts from quantum information theory. Our method uses the entanglement and correlation among molecular orbitals to analyze changes in electronic structure that accompany chemical processes. As a proof-of-principle example, the evolution of nickel-ethene bond-formation is dissected, which allows us to monitor the interplay of back-bonding and pi-donation along the reaction coordinate. Furthermore, the reaction pathway of nickel-ethene complexation is analyzed using quantum chemistry methods, revealing the presence of a transition state. Our study supports the crucial role of metal-toligand back-donation in the bond-forming process of nickel-ethene.
First author: Monakhov, KY, Supramolecular Recognition Influences Magnetism ing [X@(HV8V14O54)-V-IV-O-V](6-) Self-Assemblies with Symmetry-Breakingg Guest Anions, CHEMISTRY-A EUROPEAN JOURNAL, 21, 2387, (2015)
Abstract: Mixed-valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all-inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self-assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra-weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {(V22O54)-O-IV/V}-type polyoxoanions of D-2d symmetry enclosing diamagnetic VO2F2- (C-2v), SCN- (C-v), or ClO4- (T-d) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V22O54} shells. We also include the synthesis and characterization of the novel [(VO2F2)-O-V@(HV8V14O54)-V-IV-O-V](6-) system that comprises the rarely encountered discrete difluorovanadate anion as a quasi-isolated guest species.
First author: Frei, R, General and Practical Formation of Thiocyanates from Thiols, CHEMISTRY-A EUROPEAN JOURNAL, 21, 2662, (2015)
Abstract: A new method for the cyanation of thiols and disulfides using cyanobenziodoxol(on)e hypervalent iodine reagents is described. Both aliphatic and aromatic thiocyanates can be accessed in good yields in a few minutes at room temperature starting from a broad range of thiols with high chemioselectivity. The complete conversion of disulfides to thiocyanates was also possible. Preliminary computational studies indicated a low energy concerted transition state for the cyanation of the thiolate anion or radical. The developed thiocyanate synthesis has broad potential for various applications in synthetic chemistry, chemical biology and materials science.
First author: Suaud, N, Accuracy of Embedded Fragment Calculation for Evaluating Electrong Interactions in Mixed Valence Magnetic Systems: Study of 2e-Reducedg Lindqvist Polyoxometalates, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 550, (2015)
Abstract: Accurate quantum chemical calculations on real-world magnetic systems are challenging, the inclusion of electron correlation being the bottleneck of such task. One method proposed to overcome this difficulty is the embedded fragment approach. It tackles a chemical problem by dividing it into small fragments, which are treated in a highly accurate way, surrounded by an embedding included at an approximate level. For the vast family of medium-to-large sized polyoxometalates, two-electron-reduced systems are habitual and their magnetic properties are interesting. In this paper, we aim at assessing the quality of embedded fragment calculations by checking their ability to reproduce the electronic spectra of a complete system, here the mixed-metal series [MoxW6xO19](4) (x = 06). The microscopic parameters extracted from fragment calculations (electron hopping, intersite electrostatic repulsion, local orbital energy, etc.) have been used to reproduce the spectra through model Hamiltonian calculations. These energies are compared to the results of the highly accurate ab initio difference dedicated configuration interaction (DDCI) method on the complete system. In general, the model Hamiltonian calculations using parameters extracted from embedded fragments nearly exactly reproduce the DDCI spectra. This is quite an important result since it can be generalized to any inorganic magnetic system. Finally, the occurrence of singlet or triplet ground states in the series of molecules studied is rationalized upon the interplay of the parameters extracted.
First author: Li, B, Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueousg redox flow battery, NATURE COMMUNICATIONS, 6, 550, (2015)
Abstract: Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (similar to 25Wh l(-1)). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167 Wh l(-1) is demonstrated with a near-neutral 5.0 M Znl(2) electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from -20 to 50 degrees C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.
First author: Wiegand, T, Structural Characterization of Frustrated Lewis Pairs and Their Reactiong Products Using Modern Solid-State NMR Spectroscopy Techniques, ISRAEL JOURNAL OF CHEMISTRY, 55, 150, (2015)
Abstract: Frustrated Lewis pair (FLP) chemistry has provided a new strategy for small-molecule binding and/or catalytic activation. The most prominent FLPs are based on intramolecular phosphane-borane adducts, the catalytic properties of which can be tailored over wide ranges of reactivity and selectivity. Advanced solid-state NMR spectroscopic techniques, together with DFT calculations, can provide new structural insights in these systems. This review illustrates the utility of P-31 and B-11 NMR chemical shifts, 11B electric field gradient tensors, and P-31-B-11 indirect and direct dipole-dipole interactions for characterizing intramolecular borane-phosphane FLPs. We demonstrate the potential of this method to 1) quantify the extent of boron-phosphorus bonding interactions (and hence, the "degree of frustration"); 2) reveal specific structural details (i.e., boron-phosphorus distances and other local geometric aspects) related to their catalytic activities; and (3) characterize products of FLP reactions with regard to molecular structure, stereochemistry, and aggregation properties in terms of internuclear distances, bonding connectivities, and orientational parameters.
First author: Devarajan, D, Is There a Need to Discuss Atomic Orbital Overlap When Teachingg Hydrogen-Halide Bond Strength and Acidity Trends in Organic Chemistry?, JOURNAL OF CHEMICAL EDUCATION, 92, 286, (2015)
Abstract: Undergraduate organic chemistry textbooks and Internet websites use a variety of approaches for presenting and explaining the impact of halogen atom size on trends in bond strengths and/or acidity of hydrogen halides. In particular, several textbooks and Internet websites explain these trends by invoking decreasing orbital overlap between the hydrogen is atomic orbital and successively larger group 17 halogen atomic orbitals. A similar orbital overlap rationalization is often extended to the trends in alkyl halide bond strengths. We examined this orbital overlap explanation using quantum mechanical calculations. Calculations reveal that orbital overlap increases rather than decreases with successively larger group 17 halogen atomic orbitals. This suggests that an orbital overlap explanation is physically incorrect and unneeded. Alternative to orbital overlap, we briefly discuss physically correct models for rationalizing halogen bond strength and acidity based on quantum mechanical valence bond theory and molecular orbital theory.
First author: Ciancaleoni, G, Counterion Effect in the Reaction Mechanism of NHC Gold(I)-Catalyzedg Alkoxylation of Alkynes: Computational Insight into Experiment, ACS CATALYSIS, 5, 803, (2015)
Abstract: Experimental data suggest that anions that provide a compromise between the hydrogen-bond acceptor and the coordinating powers rather than poor coordinating anions unexpectedly increase the efficiency of L-Au-X (L = ligand, X = anion) catalyzed alkyne alkoxylation reactions, where the nucleophilic attack is the rate-determining step. No systematic computational studies about the role of the anion in the different steps of the catalytic cycle are available yet. In this paper, the remarkable anion influence on the catalytic efficiency of [NHCAuX] (X = BF4-, OTf-, OTs-, TFA(-), and OAC(-)) complexes in the intermolecular addition of methanol to 2-butyne process has been analyzed through a density functional theory (DFT) approach. The role of the anion has been considered in all the steps of the reaction mechanism: pre-equilibrium, nucleophilic addition, and protodeauration. In the nucleophilic attack step, the anion acts (i) as a template, holding the methanol in the right position for the outer-sphere attack; (ii) as a hydrogen-bond acceptor, enhancing the nucleophilicity of the attacking methanol; (iii) as catalyst deactivator, by either its strong coordinating and/or basicity power, preventing the alkyne coordination or forming free alkoxide, respectively. In the protodeauration step, the anion acts as a proton shuttle, lowering the activation barrier. DFT calculations support intermediate coordinating and basicity power anions as the most efficient catalysts.
First author: Vijayakumar, M, Understanding Aqueous Electrolyte Stability through Combinedg Computational and Magnetic Resonance Spectroscopy: A Case Study ong Vanadium Redox Flow Battery Electrolytes, CHEMPLUSCHEM, 80, 428, (2015)
Abstract: The investigation of the vanadium electrolyte stability issue on the molecular-level solvation structure and the dynamics has led to the successful designing of mixed acid-based vanadium electrolytes. This new mixed-acid based electrolyte system render approximately 70% increase in energy density (approximate to 40 WhL(-1)) and approximately 80% increase in stable temperature window (-10 to +50 degrees C) compared with conventional sulfuric acid-based vanadium electrolyte. Through a comprehensive study by density functional theory and nuclear magnetic resonance spectroscopies, the improved stability is attributed to the hydrochloric acid as optimal cosolvent providing chloride anions for a ligand-exchange process in the vanadium solvation structure. The role of the chloride counteranion in the solvation structure and dynamics of vanadium species was studied using combined magnetic resonance spectroscopy and DFT-based theoretical methods. The solvation phenomenon of multiple vanadium species and their impact on vanadium redox flow battery electrolyte chemical stability are discussed.
First author: Morgenstern, A, In search of an intrinsic chemical bond, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1053, 31, (2015)
Abstract: The chemical bond, as a link between atoms, is an intrinsic property of the charge density. However, bond energy, which is commonly seen as the energy difference between a molecular state and an arbitrary dissociated state, depends extrinsically on the charge density. This view of a bond as a natural link possessing properties that are externally determined is at best clumsy, and often leads to contradictory interpretations as to the origins of the structure and properties of molecules and solids. Ideally, one would like to uncover an intrinsic property of the chemical bond that gives similar information content as that provided by bond energy. To this end, we report on our ongoing work exploring the intrinsic geometry imposed on the charge density by mapping it onto the smallest volumes bounded by zero flux surfaces in the gradient of the charge density. These natural volume elements of the Quantum Theory of Atoms in Molecules have well defined properties, and hence, this mapping produces a set of property distributions with a quantifiable geometric structure that varies from molecule to molecule. Here, we examine the intrinsic geometry of the kinetic energy distribution for a series of homonuclear dimers and compare the geometric properties of these distributions with the bond energies of the same dimers.
First author: Alonso, M, Scrutinizing ion-pi and ion-sigma interactions using the noncovalentg index and energy decomposition analysis, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1053, 150, (2015)
Abstract: The nature and origin of ion-pi and ion-sigma interactions has been systematically investigated using dispersion-corrected density functional theory and the recently developed noncovalent interaction (NCI) method. A detailed analysis of these interactions is performed with the aim to identify the requirements that have to be fulfilled by the molecular system for strong ion-ligand interactions. Interestingly, our results indicate that aliphatic systems, such as cyclohexane, can interact as strong as aromatic ones with both cations and anions, despite of having a negligible quadrupole moment. In fact, cyclohexane binds anions stronger than benzene itself but slightly weaker that hexafluorobenzene. The NCI method reveals that the interaction between the ions and three C-H bonds of the saturated fragment are responsible for the surprisingly strong ion-sigma interaction. A weakening of the ion-sigma interactions is observed in the order: Li+ > F- > Na+ Cl- > Br- approximate to K+. In addition, a complete Ziegler-Rauk type energy decomposition analysis has been carried out in order to reveal the origins of the thermodynamic driving force for complex formations. The electron density deformation upon complex formation has been scrutinized with a complementary NOCV analysis allowing the identification of molecular orbital interaction contributions to the stabilization. Based on these analysis, it is shown that the formally anion-pi interaction is rather an anion-sigma* interaction.
First author: Muratov, DV, Dicationic mu-Diborolyl Arene Triple-Decker Complexesg [CpCo(mu-1,3-C3B2Me5)M(arene)](2+) (M = Rh, Ir; Cp = Cyclopentadienyl):g Synthesis, Structures, Electrochemistry and Bonding, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 1053, 804, (2015)
Abstract: The reaction of the bromide complexes [CpCo(-1,3-C3B2Me5)MBr2](2) [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) -diborolyl triple-decker complexes [CpCo(-1,3-C3B2Me5)M(MeCN)(3)](2+) [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(-1,3-C3B2Me5)M(MeNO2)(3)](2+), generated in a similar way, react with benzene and its methylated derivatives to give the arene triple-decker complexes [CpCo(-1,3-C3B2Me5)M(arene)](2+) [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5-Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)(2), 5c(BF4)(2), 6b(BF4)(2) and 6c(BF4)(2) were determined by X-ray diffraction. The electron-transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one-electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a (64) hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh-benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)](2+); however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene.
First author: Roszak, R, s-Block metallabenzene: aromaticity and hydrogen adsorption, JOURNAL OF MOLECULAR MODELING, 21, 804, (2015)
Abstract: Second group metal dimers can replace the carbon atom in benzene to form metallabenzene (C5H6M2) compounds. These complexes possess some aromatic character and promising hydrogen adsorption properties. In this study, we investigated the aromatic character of these compounds using aromaticity indices andmolecular orbital analysis. To determine the nature of interactions between hydrogen and the metallic center, variationperturbational decomposition of interaction energy was applied together with ETS- NOCVanalysis. The results obtained suggest that the aromatic character comes from three p orbitals located mainly on the C5H5- fragment. The high hydrogen adsorption energy (up to 6.5 kcal mol(-1)) results from two types of interaction. In C5H6Be2, adsorption is controlled by interactions between the empty metal orbital and the s orbital of the hydrogen molecule (Kubas interaction) together with corresponding backdonation interactions. Other C5H6M2 compounds adsorb H-2 due to Kubas interactions enhanced by H-2-pi interactions.
First author: Gupta, KSV, Effect of the anchoring group in the performance ofg carbazole-phenothiazine dyads for dye-sensitized solar cells, DYES AND PIGMENTS, 113, 536, (2015)
Abstract: A combined experimental and theoretical study is carried out on two novel carbazole-phenothiazine dyadic dyes bearing the simple carboxylic acid and the more rarely investigated malonic acid as anchoring group. An improvement of the photovoltaic performances is observed when the malonic acid is employed in place of the carboxylic acid, even if the highest efficiencies for this family of organic dyes were recorded with the use of the cyanoacrylic and rhodanine-3-aceti acid as anchoring units. The low photocurrents measured in the case of the carboxylic anchoring are rationalized on the basis of the computational modelling of the isolated dye in solution as well as the investigation of the electronic structure of extended dye-sensitized TiO2 models. The theoretical calculations suggest that the low short current densities might arise from the unfavourable interplay of the dye's optical properties (blue shift of the absorption spectrum) and of the energy alignment between the dye's LUMO and the semiconductor conduction band edge, possibly causing an inefficient electron injection process.
First author: Mitoraj, MP, Nature of the Water/Aromatic Parallel Alignment Interactions, JOURNAL OF COMPUTATIONAL CHEMISTRY, 36, 171, (2015)
Abstract: The water/aromatic parallel alignment interactions are interactions where the water molecule or one of its OH bonds is parallel to the aromatic ring plane. The calculated energies of the interactions are significant, up to E-CCSD(T)(limit) = -2.45 kcal mol(-1) at large horizontal displacement, out of benzene ring and CH bond region. These interactions are stronger than CHO water/benzene interactions, but weaker than OH interactions. To investigate the nature of water/aromatic parallel alignment interactions, energy decomposition methods, symmetry-adapted perturbation theory, and extended transition state-natural orbitals for chemical valence (NOCV), were used. The calculations have shown that, for the complexes at large horizontal displacements, major contribution to interaction energy comes from electrostatic interactions between monomers, and for the complexes at small horizontal displacements, dispersion interactions are dominant binding force. The NOCV-based analysis has shown that in structures with strong interaction energies charge transfer of the type sigma*(OH) between the monomers also exists.
First author: Dresselhaus, T, Self-consistent embedding of density-matrix renormalization groupg wavefunctions in a density functional environment, JOURNAL OF CHEMICAL PHYSICS, 142, 171, (2015)
Abstract: We present the first implementation of a density matrix renormalization group algorithm embedded in an environment described by density functional theory. The frozen density embedding scheme is used with a freeze-and-thaw strategy for a self-consistent polarization of the orbital-optimized wavefunction and the environmental densities with respect to each other.
First author: Novoa, N, Doubly phenoxide-bridged binuclear copper(II) complexes with onog tridentate schiff base ligand: Synthesis, structural, magnetic andg theoretical studies, POLYHEDRON, 86, 81, (2015)
Abstract: The tridentate ONO-donor Schiff base ligand H2L, derived from the condensation of 1-anisyl-1,3-butane-dione and 2-aminophenol, was generated in situ and reacted with Cu(NO3)(2)center dot 3H(2)O to yield two doubly phenoxo bridged di-copper(II) complexes depending on the nitrogenous base used. [Cu2L2] (1) is obtained in 85% and 75% yield in the presence of pyridine or 4-picoline, respectively, and [(py-tBu)(2)Cu2L2] (2) is isolated in 75% yield in the presence of 4-tert-butylpyridine. Compounds 1 and 2 were characterized in the solid-state by elemental analysis and FT-IR spectroscopy. Single crystal X-ray diffraction study reveals that in 1 the two four-coordinated copper atoms adopt a square planar geometry, whereas in 2 each Cu(II) metal ion shows a five coordinate square pyramidal (ONO,N + O) geometry. In each dimer, two mu-phenolic oxygen atoms bridge the two half-units forming a planar Cu2O2 core. EPR studies in fluid solutions indicate that the dimeric structure of 1 and 2 is destroyed upon dissolution. In the solid-state, 1 is EPR silent, whereas 2 presents an unresolved broad resonance (Delta H peak-to-peak = 71.5 G) with g= 2.071 at 298 K, along with the triplet state (S = 1) signature at g= 4.181. Variable temperature (2-300 K) magnetic susceptibility measurements exhibit strong antiferromagnetic interactions between the Cu(II) centers with aJ value of -397 cm(-1) for 1, while no interaction operates between the two spins localized on Cu(II) metal ions in 2. Ab initio calculations were also performed to supplement the experimental results.
First author: Meyer, GJ, Through space interaction between ferrocenes mediated by a thioether, POLYHEDRON, 86, 125, (2015)
Abstract: A series of conformationally constrained 2,6-bisferrocenylphenyl thioethers were synthesized via Suzuki-Miyaura cross coupling reactions. Structural information was obtained using X-ray crystallography and dynamic H-1 NMR spectroscopic studies, showing highly constrained m-terphenyl systems. Interaction of the ferrocene moieties through space mediated by the sulfur were studied by ultra-violet photoelectron spectroscopy (UPS), cyclic voltammetry, differential pulse voltammetry, UV-Vis-NIR spectroscopy and DFT computations. Electrochemical results show two, fully reversible 1e(-) redox processes for the ferrocenes where the separation of peaks is affected by both solvent and supporting electrolyte, suggesting significant electrostatic interaction which is further confirmed in the gas phase by UPS studies.
First author: Fusaro, L, Direct Detection of O-17 in [Gd(DOTA)](-) by NMR Spectroscopy, CHEMISTRY-A EUROPEAN JOURNAL, 21, 1955, (2015)
Abstract: The O-17 NMR spectrum of the non-coordinated carboxyl oxygen in the Gd-III-DOTA (DOTA = tetraazacyclododecanetetraacetic acid) complex has been observed experimentally. Its line width is essentially unaffected by paramagnetic relaxation due to gadolinium, and is only affected by the quadrupole pathway. The results are supported by the relevant parameters (hyperfine and quadrupole coupling constants) calculated by relativistic DFT methods. This finding opens up new avenues for investigating the structure and reactivity of paramagnetic Gd-III complexes used as contrast agents in magnetic resonance imaging.
First author: Alegret, N, Cubane oxides inside middle-size fullerenes: the next endohedrals to beg detected?, THEORETICAL CHEMISTRY ACCOUNTS, 134, 1955, (2015)
Abstract: From a comparison with the already isolated and characterized Sc-4(mu(3)-O)(3)@C-80 metallofullerene, we propose here that an even larger 8-atom cubane oxide M-4(mu(3)-O)(4) could also be encapsulated inside other middle-size fullerenes that would formally accept four electrons. Several possibilities are suggested for M = Sc and Lu.
First author: Walen, H, Cu2S3 complex on Cu(111) as a candidate for mass transport enhancement, PHYSICAL REVIEW B, 91, 1955, (2015)
Abstract: Sulfur-metal complexes, containing only a few atoms, can open new, highly efficient pathways for transport of metal atoms on surfaces. For example, they can accelerate changes in the shape and size of morphological features, such as two-dimensional nanoclusters, over time. In this study we perform STM under conditions that are designed to specifically isolate such complexes. We find a new, unexpected S-Cu complex on the Cu(111) surface, which we identify as Cu2S3. We propose that Cu2S3 enhances mass transport in this system, which contradicts a previous proposal based on Cu3S3. We analyze bonding within these Cu-S complexes, identifying a principle for stabilization of sulfur complexes on coinage metal surfaces.
First author: Herden, B, Photon cascade emission in Pr3+ doped fluorides with CaF2 structure:g Application of a model for its prediction, CHEMICAL PHYSICS LETTERS, 620, 34, (2015)
Abstract: In this work, we predict and measure the optical behaviour of Pr3+ in different binary and ternary fluorides. We use a validated model based on Ligand Field Theory and Density Functional Theory to calculate the multiplet energy levels arising from the ground [Xe]4f(2) and excited [Xe]4f(1)5d(1) electron configurations of Pr3+ in its chemical environment. Moreover, the luminescence spectra of the considered materials were recorded. In overall the theoretical determination corroborates to the experimental findings. The phenomenon of the photon cascade emission is particularly stressed, being important for the design of modern phosphors with quantum efficiencies larger than 100%.
First author: Shao, YH, Advances in molecular quantum chemistry contained in the Q-Chem 4g program package, MOLECULAR PHYSICS, 113, 184, (2015)
Abstract: A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Moller-Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr-2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.
First author: Buda, S, Application of 2-Substituted Benzyl Groups in Stereoselectiveg Glycosylation, JOURNAL OF ORGANIC CHEMISTRY, 80, 770, (2015)
Abstract: The use of 2-O-(2-nitrobenzyl) and 2-O-(2-cyanobenzyl) groups controls stereoselective formation of 1,2-trans-glycosidic linkages via the arming participation effect. The observed stereoselectivity likely arises from the intramolecular formation of cyclic intermediate between the electron-rich substituent and the donor oxacarbenium ion providing the expected facial selectivity for attack of the glycoside acceptor. The stereodirecting effect of the 2-nitro- and 2-cyanobenzyl groups attached at the remote position (C-3, C-4, and C-6) of the donor molecule have also been investigated. To prove the postulated mechanism based on the participation effect of 2-substituted benzyl groups in the glycosylation stereoselectivity we used DFT theoretical calculation methodology.
First author: Nowak, P, Analytical aspects of achiral and cyclodextrin-mediated capillaryg electrophoresis of warfarin and its two main derivatives assisted byg theoretical modeling, JOURNAL OF CHROMATOGRAPHY A, 1377, 106, (2015)
Abstract: Several distinct analytical issues have been addressed by performing capillary electrophoresis-based separations of the warfarin, 7-hydroxywarfarin and 10-hydroxywarfarin in an achiral and cyclodextrin-containing media. The measurements were conducted across a range of pH in order to find optimum conditions for achiral and chiral separations. The values of acid dissociation constant (pK(a)) have been determined and compared. Subsequently, after performing a series of mobility shift assays at different pH and cyclodextrin concentration, the pK(a) values ascribed to diastereomeric complexes with methyl-beta-cyclodextrin have been estimated. The significant pK(a) shifts upon complexation have been noticed for warfarin – up to 1.5 pH units, and only subtle for 10-hydroxywarfarin. A new approach that allows the estimation of association percentage based on the electrophoretic mobility curves has been also demonstrated. The complex mechanism of chiral separation has been found to be responsible for the observed migration profile, relying on a combined equilibrium between complexation/partition and protonation/deprotonation phenomena. The occurrence of the pK(a)-related migration order reversal has been demonstrated in achiral medium between warfarin and 7-hydroxywarfarin, and in chiral medium between enantiomers, causing a drop in enantioselectivity at specific pH. In parallel, the density functional theory-based calculations have been performed in order to obtain the structures of warfarin and its derivatives as well as to rationalize the shifts in pK(a) values.
First author: Dumont, E, Interaction of Palmatine with DNA: An Environmentally Controlledg Phototherapy Drug, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 410, (2015)
Abstract: Palmatine is one of the four main protoberberine alkaloids and is largely employed in pharmacy and medicine as a versatile drug with considerable biological activities. More recently, palmatine has been proposed as a promising DNA phototherapy drug, notably due to its ability to produce in situ singlet oxygen only when interacting with DNA. The fine mechanisms of palmatineDNA interactions as well as its complicated photophysics are not yet fully understood. In this paper, we identify via molecular dynamic techniques two stable interaction modes between palmatine and B-DNA, namely insertion and minor groove binding, whose structural and electronic bases are analyzed and rationalized. These two competitive modes share the same UVvis signature and estimated binding free energies, and thus they may indeed coexist. By using hybrid quantum mechanics/molecular mechanics protocols coupled to molecular dynamics, we analyze palmatine excited state properties in water solution and in interaction with DNA. The environmentally controlled production of singlet oxygen is thus rationalized in terms of the competition between local and charge-transfer excited states.
First author: Ospadov, E, A pure-sampling quantum Monte Carlo algorithm, JOURNAL OF CHEMICAL PHYSICS, 142, 410, (2015)
Abstract: The objective of pure-sampling quantum Monte Carlo is to calculate physical properties that are independent of the importance sampling function being employed in the calculation, save for the mismatch of its nodal hypersurface with that of the exact wave function. To achieve this objective, we report a pure-sampling algorithm that combines features of forward walking methods of pure-sampling and reptation quantum Monte Carlo (RQMC). The new algorithm accurately samples properties from the mixed and pure distributions simultaneously in runs performed at a single set of time-steps, over which extrapolation to zero time-step is performed. In a detailed comparison, we found RQMC to be less efficient. It requires different sets of time-steps to accurately determine the energy and other properties, such as the dipole moment. We implement our algorithm by systematically increasing an algorithmic parameter until the properties converge to statistically equivalent values. As a proof in principle, we calculated the fixed-node energy, static alpha polarizability, and other one-electron expectation values for the ground-states of LiH and water molecules. These quantities are free from importance sampling bias, population control bias, time-step bias, extrapolation-model bias, and the finite-field approximation. We found excellent agreement with the accepted values for the energy and a variety of other properties for those systems.
First author: Wei, HL, Theoretical investigation on electron mobility properties ofg anthracenedicarboximide derivatives based n-type organic semiconductors, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48, 410, (2015)
Abstract: The anthracenedicarboximide (ADI) based n-type organic semiconductor materials, ADIF-Br-2 and ADIF-CN2, and eight designed ADI derivatives are systematically studied using density functional theory. The eight derivatives are designed by substituting atoms and functional groups in the middle positions of the molecules and by adding functional groups at the end of the molecules. The structures, optical properties, ionization potential, electronic affinity, reorganization energy, charge coupling and charge mobility of the compounds are found to be largely influenced by the substitutions. According to the main characters of organic semiconductors, ADIF-Br-2 is suggested as a good n-type organic semiconductor, and ADIF-CN2 as an ambipolar organic semiconductor. Compared to ADIF-Br-2 and ADIF-CN2, all the eight designed derivations are suggested as good n-type organic semiconductors with improved performance. The main absorption spectra of the compounds are in the range 400-500 nm, which match well with the solar spectrum. The hydrogen bonds formed in ADIF-Br-2 and ADIF-CN2 make a close pi-pi stacking, which accounst for their large charge mobility (0.208 and 0.057 cm(2) V-1 s(-1), respectively). The hydrogen bond is suggested as a new mechanism for charge mobility in organic semiconductors.
First author: Song, XD, Effect of CH3OH on the luminescent properties of theg [Zn(sfdb)(bpy)(H2O)](n) center dot 0.5nCH(3)OH metal-organic framework, CHEMICAL PHYSICS, 446, 65, (2015)
Abstract: The influence of CH3OH solvent on the luminescent properties of the [Zn(sfdb)(bpy)(H2O)](n) center dot 0.5nCH(3)OH (sfdb = 4,4-sulfonyldibenzoic acid, bpy = 2,2-bipyridine) metal-organic framework (MOF) was investigated by considering the hydrogen bond between CH3OH and [Zn(sfdb)(bpy)(H2O)](n) in an electronically excited state using density functional theory and time-dependent density functional theory methods. The calculated geometry, infrared spectrum, and UV-vis spectrum in the ground state are consistent with the experimental results. The frontier molecular orbitals and electronic configuration indicated that the origin of the luminescence is ligand-to-ligand charge transfer rather than ligand-to-metal charge transfer, as has been previously proposed. We found that the O3 center dot center dot center dot H11 hydrogen bond is weaker in the excited state than in the ground state, and the weaker hydrogen bond in the electronically excited state should enhance the luminescence. The results show that the CH3OH solvent changes the luminescence properties of [Zn(sfdb)(bpy)(H2O)](n), which provides potential opportunities for the design of diverse luminescent MOFs.
First author: Dobkowski, J, Substituent and Solvent Effects on the Excited State Deactivationg Channels in Anils and Boranils, CHEMISTRY-A EUROPEAN JOURNAL, 21, 1312, (2015)
Abstract: Differently substituted anils (Schiff bases) and their boranil counterparts lacking the proton-transfer functionality have been studied using stationary and femtosecond time-resolved absorption, fluorescence, and IR techniques, combined with quantum mechanical modelling. Dual fluorescence observed in anils was attributed to excited state intramolecular proton transfer. The rate of this process varies upon changing solvent polarity. In the nitro-substituted anil, proton translocation is accompanied by intramolecular electron transfer coupled with twisting of the nitrophenyl group. The same type of structure is responsible for the emission of the corresponding boranil. A general model was proposed to explain different photophysical responses to different substitution patterns in anils and boranils. It is based on the analysis of changes in the lengths of CN and CC bonds linking the phenyl moieties. The model allows predicting the contributions of different channels that involve torsional dynamics to excited state depopulation.
First author: Fustier, M, Scandium Carbene Complexes: Synthesis of Mixed Alkyl, Amido, andg Phosphido Derivatives, ORGANOMETALLICS, 34, 63, (2015)
Abstract: Different synthetic strategies are proposed to obtain a family of scandium carbene complexes. Starting either from scandium trichloride, scandium trisbenzyl, or the known scandium bis(diphenylthiophosphinoyl)methanediide chloride complex 1, the homoleptic bis-carbene complex [Sc{C(PPh2S)(2)}(2)Li(THF)(2)] (3), the alkyl-carbene complex [Sc{C(PPh2S)(2)}{CH(PPh2S)(2)}(THF)] (5), the amido-carbene complex [Sc{C(PPh2S)(2)}{N(SiMe3)(2)}(THF)] (7), and the phosphido-carbene complex [Sc{C(PPh2S)(2)}{P(SiMe3)(2)}(Py)2] (8) were obtained. The influence of the nature of the anionic ligand in trans position to the carbene ligand on the geometries at Sc was probed by DFT calculations in the case of complexes 7 and 8.
First author: Bauer, G, Iron Pincer Complexes as Catalysts and Intermediates in Alkyl Arylg Kumada Coupling Reactions, ORGANOMETALLICS, 34, 289, (2015)
Abstract: Iron-catalyzed alkylaryl Kumada coupling has developed into an efficient synthetic method, yet its mechanism remains vague. Here, we apply a bis(oxazolinylphenyl)amido pincer ligand (Bopa) to stabilize the catalytically active Fe center, resulting in isolation and characterization of well-defined iron complexes whose catalytic roles have been probed and confirmed. Reactivity studies of the iron complexes identify an Fe(II) ate complex, [Fe(Bopa-Ph)(Ph)(2)]-, as the active species for the oxidative addition of alkyl halide. Experiments using radical-probe substrates and DFT computations reveal a bimetallic and radical mechanism for the oxidative addition. The kinetics of the coupling of an alkyl iodide with PhMgCl suggests that formation of the ate complex, rather than oxidative addition, is the turnover-determining step. This work provides insights into iron-catalyzed cross-coupling reactions of alkyl halides.
First author: Caldwell, LM, Thioxoethenylidene (CCS) as a Bridging Ligand, ORGANOMETALLICS, 34, 328, (2015)
Abstract: The reaction of [Mo( CBr)(CO)(2)(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with [Fe-2(mu-SLi)(2)(CO)(6)] affords, inter alia, the unsymmetrical binuclear thioxoethenylidene complex [Mo-2(mu,sigma(C):eta(2)(C'S)-CCS)(CO)(4)(Tp*)(2)], which may be more directly obtained from [Mo( CBr)(CO)(2)(Tp*)] and Li2S. The reaction presumably proceeds via the intermediacy of the bis(alkylidynyl)thioether complex S{CgMo(CO)(2)(Tp*)}(2), which was, however, not directly observed but explored computationally and found to lie 78.6 kJ mol(-1) higher in energy than the final thioxoethenylidene product. Computational interrogation of the molecules [M-2(mu-C2S)(CO)(2)(Tp*)(2)] (M = Mo, W, Re, Os) reveals three plausible coordination modes for a thioxoethenylidene bridge which involve a progressive strengthening of the C-C bond and weakening of the M-C and M-S bonds, as might be expected from simple effective atomic number considerations.
First author: Miorelli, J, A Full Topological Analysis of Unstable and Metastable Bond Criticalg Points, CHEMPHYSCHEM, 16, 152, (2015)
Abstract: Researchers are developing conceptually based models linking the structure and dynamics of molecular charge density to certain properties. Here we report on our efforts to identify features within the charge density that are indicative of instability and metastability. Towards this, we use our extensions to the quantum theory of atoms in molecules that capitalize on a molecule's ridges to define a natural simplex over the charge density. The resulting simplicial complex can be represented at various levels by its 0-, 1-, and 2-skeleton (dependent sets of points, lines, and surfaces). We show that the geometry of these n-skeletons retains critical information regarding the structure and stability of molecular systems while greatly simplifying charge density analysis. As an example, we use our methods to uncover the fingerprints of instability and metastability in two much-discussed systems, that is, the di-benzene complex and the He and adamantane inclusion complex.
First author: Conradie, MM, Electrochemical behaviour of Tris(beta-diketonato)iron(III) complexes: Ag DFT and experimental study, ELECTROCHIMICA ACTA, 152, 512, (2015)
Abstract: A combined experimental and theoretical study on the electrochemical behaviour of a series of tris (beta-diketonato) iron(III) complexes is reported. The experimental cyclic voltammetric data showed the reversible reduction and reoxidation of Fe-III/Fe-II. A diffusion coefficient of 5.6 x 10(-6) cm(2) s(-1) was obtained for tris(acetonato) iron(III) in acetonitrile. Linear relationships and trends obtained between the formal reduction potential of Fe-III/Fe-II in tris(beta-diketonato) iron(III) complexes and those electronic parameters describing the electron donating ability of the beta-diketonato ligand, such as the Gordy scale group electronegativities, and the Hammett meta substituent constants of the side groups R-1 and R-2 on the beta-diketonato ligand ((RCOCHCOR2)-C-1)-, the Lever electronic parameters and the pK(a) of the free beta-diketone ligand, are presented. The experimental formal reduction potential relates linearly to the density functional theory calculated electron affinity, as well as to the energy of the lowest unoccupied molecular orbital of the tris(beta-diketonato) iron(III) complexes.
First author: Huang, JD, Impact of Edge-Core Structures and Substituent Effects on the Electronicg and Charge-Transport Properties of Heteroaromatic Ring-Fused Oligomers, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 33, (2015)
Abstract: Herein, we systematically studied the electronic and conducting properties of the thiophene-fused polycyclic aromatic compounds and their analogues and discussed in detail the influences of edge-core structure, heteroatom substitution, and functionalization on their field-effect transistor properties and solid-state packing motifs. It was found that the influence of edge-core structure and heteroatom substitution on the electronic properties and reorganization energies of semiconducting materials mainly originates from the variations of the frontier molecular orbital charge distributions and the steric hindrance as well as the conjugate degree of compounds. Moreover, our results also showed that the fusion of benzene rings at the longitudinal end could effectively decrease energy barrier of charge injection and reorganization energies and change the molecular arrangement from herringbone packing to p stacking, which provides a promising way to functionalize organic semiconducting molecules.
First author: Asaduzzaman, A, Substitution Effects on the Water Oxidation of Ruthenium Catalysts: Ag Quantum-Chemical Look, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 242, (2015)
Abstract: Quantum chemistry has been used to investigate the oxidation of water by a family of seven catalysts based on [Ru(tpy)(bpy)(OH2)](2+) (tpy = 2,2′:6′,2"-terpyridine, bpy = 2,2′-bipyridine). The electron-donating -OMe and -NH2 groups (EDG) and electron-withdrawing -COOH and -NO2 groups (EWG) are installed in the catalyst by replacing hydrogen atoms on the bpy and tpy ligands. The EDG induces an increase in the electron density at the Ru center, whereas the EWG does the opposite. Reduced electron density at the metal center facilitates Ru(N+1)/Ru(N) reduction and thus a higher reduction potential. Catalytic evolution of one oxygen molecule from two water molecules using all catalysts is an exothermic process if driven by Ce-IV. The exothermicity increases from EDG to EWG via parents. Regarding intermediates, the singlet states of 7-coordinated catalysts are slightly more stable than the triplet states of 6-coordinated catalysts for most catalysts. Only for a strong EWG (-NO2) containing catalyst, the triplet 6-coordinated states complex is the most stable. Calculated Ru-O and O-O distances suggest that oxygen will be liberated favorably from the triplet state of 6-coordinated complexes, whose stability increase (with respect to the singlet of 7-coordinated complexes) with increasing electron-withdrawing nature.
First author: Vitova, T, Polarization Dependent High Energy Resolution X-ray Absorption Study ofg Dicesium Uranyl Tetrachloride, INORGANIC CHEMISTRY, 54, 174, (2015)
Abstract: Dicesium uranyl tetrachloride (Cs2UO2Cl4) has been a model compound for experimental and theoretical studies of electronic structure of U(VI) in the form of UO22+ (uranyl ion) for decades. We have obtained angle-resolved electronic structure information for oriented Cs2UO2Cl4 crystal, specifically relative energies of 5f and 6d valence orbitals probed with extraordinary energy resolution by polarization dependent high energy resolution X-ray absorption near edge structure (PD-HR-XANES) and compare these with predictions from quantum chemical Amsterdam density functional theory (ADF) and ab initio real space multiple-scattering Green's function based FEFF codes. The obtained results have fundamental value but also demonstrate an experimental approach, which offers great potential to benchmark and drive improvement in theoretical calculations of electronic structures of actinide elements.
First author: Garcia-Fernandez, P, Origin of the Exotic Blue Color of Copper-Containing Historical Pigments, INORGANIC CHEMISTRY, 54, 192, (2015)
Abstract: The study of chemical factors that influence pigment coloring is a field of fundamental interest that is still dominated by many uncertainties. In this Article, we investigate, by means of ab initio calculations, the origin of the unusual bright blue color displayed by historical Egyptian Blue (CaCuSi4O10) and Han Blue (BaCuSi4O10) pigments that is surprisingly not found in other compounds like BaCuSi2O6 or CaCuO2 containing the same CuO46- chromophore. We show that the differences in hue between these systems are controlled by a large red-shift (up to 7100 cm(-1)) produced by an electrostatic field created by a lattice over the CuO46- chromophore from the energy of the 3z(2)-r(2) -> x(2)-y(2) transition, a nonlocal phenomenon widely ignored in the realm of transition metal chemistry and strongly dependent upon the crystal structure. Along this line, we demonstrate that, although SiO44- units are not involved in the chromophore itself, the introduction of sand to create CaCuSi4O10 plays a key role in obtaining the characteristic hue of the Egyptian Blue pigment. The results presented here demonstrate the opportunity for tuning the properties of a given chromophore by modifying the structure of the insulating lattice where it is located.
First author: Niu, WX, Gas-Phase Ammonia Activation by Th, Th+, and Th2+ : Reaction Mechanisms,g Bonding Analysis, and Rate Constant Calculations, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 115, 6, (2015)
Abstract: The gas-phase reactions of Th, Th+, and Th2+ with NH3 were systematically investigated using different approaches of density functional theory. A detailed description of the reaction mechanisms along with the bonding character analysis offers deep insights into the reaction of Th species. Different possible spin multiplicities were considered as well as the effect of spin-orbit interactions. The analyses of results indicate that the reactions of Th species with NH3 have two types of reaction channel: isomerization and dehydrogenation. These dehydrogenation reactions are found to be exothermic, with the best thermochemical conditions observed for Th2++NH3. The bonding properties of the species involved in the reaction pathways were investigated by means of diverse analyses including electron localization function, atoms in molecules, and natural bond orbital. Reaction rate constants were computed between 298 and 2000 K at levels of variational transition state theory with the Wigner and Eckart tunneling correction. The computed results are compared with the available experimental values. A comparison with previously studied reactions of Th species with H2O and CH4 as well as U species with NH3 is performed to obtain similarities and differences of the insertion reactions of actinide atom and cations.
First author: Haruta, N, Reactivity of Endohedral Metallofullerene La-2@C-80 in Nucleophilic andg Electrophilic Attacks: Vibronic Coupling Density Approach, JOURNAL OF ORGANIC CHEMISTRY, 80, 141, (2015)
Abstract: The regioselectivities of La2@C80 in thermal nucleophilic and electrophilic attacks were theoretically investigated using vibronic coupling density (VCD) analysis. Nucleophilic and electrophilic cycloadditions to La2@C80 were experimentally reported to yield [6,6] and [6,5] adducts, respectively, as major products. VCD analysis provided a clear explanation for these experimental results. For nucleophilic reactions, it was found that the reactive [6,6] bonds did not have a large lowest unoccupied molecular orbital (LUMO) density and Fukui function but a large potential derivative with respect to a reaction mode. The VCD illustrates the origin of the interaction between the electronic and vibrational states. On the other hand, conventional reactivity indices such as frontier orbital density take only the electronic state into account. The result suggested that the stabilization due to vibronic couplings plays an important role in the regioselectivity of nucleophilic cycloadditions. The VCD with respect to the effective mode could provide a picture of the functional groups, which are the double bonds of ethylene moieties. VCD analysis with respect to hypothetical localized modes enabled the quantitative prediction of regioselectivities.
First author: Talbot, A, Activation-Strain Analysis Reveals Unexpected Origin of Fast Reactivityg in Heteroaromatic Azadiene Inverse-Electron-Demand Diels-Alderg Cycloadditions, JOURNAL OF ORGANIC CHEMISTRY, 80, 548, (2015)
Abstract: Heteroaromatic azadienes, especially 1,2,4,5-tetrazines, are extremely reactive partners with alkenes in inverse-electron-demand Diels-Alder reactions. Azadiene cycloaddition reactions are used to construct heterocycles in synthesis and are popular as bioorthogonal reactions. The origin of fast azadiene cycloaddition reactivity is classically attributed to the inverse frontier molecular orbital (FMO) interaction between the azadiene LUMO and alkene HOMO. Here, we use a combination of ab initio, density functional theory, and activation-strain model calculations to analyze physical interactions in heteroaromatic azadiene-alkene cycloaddition transition states. We find that FMO interactions do not control reactivity because, while the inverse FMO interaction becomes more stabilizing, there is a decrease in the forward FMO interaction that is offsetting. Rather, fast cycloadditions are due to a decrease in closed-shell Pauli repulsion between cycloaddition partners. The kinetic-thermodynamic relationship found for these inverse-electron-demand cycloadditions is also due to the trend in closed-shell repulsion in the cycloadducts. Cycloaddition regioselectivity, however, is the result of differences in occupied-unoccupied orbital interactions due to orbital overlap. These results provide a new predictive model and correct physical basis for heteroaromatic azadiene reactivity and regioselectivity with alkene dieneophiles.
First author: Roos, G, How the disulfide conformation determines the disulfide/thiol redoxg potential, JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS, 33, 93, (2015)
Abstract: Protein disulfides can adopt a wide variety of conformations, each having different energies. Limited experimental data suggest that disulfides adopting a high energy have an enhanced likelihood for reduction, but the exact nature of this relation is not clear. Using a computational approach, we give insight on the conformational dependence of the redox behavior of the disulfide bond, which relates structure to reactivity. The relative energy of different conformations of the diethyl disulfide model system correlates with the disulfide/thiol redox potential E degrees. Insight in the calculated redox potentials is obtained via quantitative molecular orbital theory, and via the decomposition of E degrees into a vertical electron affinity and a subsequent reorganization term. We have identified the determinants of the disulfide conformational energies and characterized the barrier to rotation around the disulfide bond. Our findings on the diethyl disulfide model system can be transferred to examples from the Protein Data Base. In conclusion, strained disulfide conformations with a high conformational energy have a large tendency to be reduced. Upon reduction, unfavorable interactions are released. This explains why reorganization effects and not a higher tendency to accept electrons account for the high reduction potential of high-energy disulfides.
First author: Szatylowicz, H, Substituent Effects in Heterocyclic Systems, ADVANCES IN HETEROCYCLIC CHEMISTRY, VOL 116, 116, 137, (2015)
Abstract: The substituent effect is one of the most important concepts in chemistry, biochemistry, and related fields. In this chapter, we collected the works devoted to this issue in relation to heterocyclic compounds and published mainly after 2000. Due to the wide range of properties, heterocycles find their applications in medical, pharmaceutical, and other fields of chemistry. Importantly, substituents incorporated in the different positions of molecules may serve as effective tool for modification of various characteristics and physicochemical properties of the heterocycles. Effects of substituents in the heterocycles containing one heteroatom: nitrogen, oxygen, sulfur, and some other ones, are reviewed in order of increasing ring size and the number of rings, followed by compounds with two or more various heteroatoms. Due to their great importance, nucleic acid bases and their analogs are presented in a separate section. The substituent effect is demonstrated by classical approaches and some modern ones. Where possible, the comparison with carbocyclic compounds is presented.
First author: Kato, S, Diversity-oriented synthesis of tetrathia[8]circulenes by sequential C-Hg borylation and annulation, CHEMICAL COMMUNICATIONS, 51, 16944, (2015)
Abstract: We have succeeded in the diversity-oriented synthesis of tetrathia[8]circulenes by sequential C-H borylation and annulation from cyclic tetrathiophene, and time-resolved microwave conductivity studies have proved that the intrinsic hole mobilities of tetrathia[8]circulenes are dependent on the chain length of the alkyl substituents at the peripheral positions.
First author: Mandal, S, A smart rhodamine-pyridine conjugate for bioimaging of thiocyanate ing living cells, RSC ADVANCES, 5, 103350, (2015)
Abstract: A rhodamine-pyridine conjugate, REDA-2PC, can selectively detect NCS- in human embryonic kidney 293 (HEK293) cells. DFT calculations suggest that this is due to non-covalent interactions (hydrogen bonding N-H center dot center dot center dot NCS-, pi-pi stacking) and long range electrostatic forces acting between the sulfur atom of the NCS- anion and the NEt2 unit of REDA-2PC. A visible light excitable probe allows fluorescence and naked eye detection of nanomolar NCS-, much lower than normal NCS- levels in the human body. A "lock" and "key" sensing mechanism is established and compared with the corresponding fluorescein derivative as a model compound.
First author: Gruden, M, Spin state relaxation of iron complexes: The case for OPBE and S12g, JOURNAL OF THE SERBIAN CHEMICAL SOCIETY, 80, 1399, (2015)
Abstract: The structures of nine iron complexes that show a diversity of experimentally observed spin ground states were optimized and analyzed using the Density Functional Theory (DFT). An extensive validation study of the new S12g functional was performed, with a discussion concerning the influence of the environment, geometry and its overall performance based on a comparison with the well-proven OPBE functional. The OPBE and S12g functionals gave the correct spin ground state for all investigated iron complexes. Since S12g performs remarkably well, it could be considered a reliable tool for studying the energetics of the spin state in complicated transition metal systems.
First author: Mathivathanan, L, A trigonal prismatic Cu-6-pyrazolato complex containing a mu(6)-F ligand, DALTON TRANSACTIONS, 44, 20685, (2015)
Abstract: The encapsulation of a fluoride ion in a trigonal prismatic Cu-6(II)-pyrazolato cage results in a small expansion of the Cu-6-host. The structural, electronic and magnetic features of the Cu-6-complex, containing an endohedral fluoride in the rare mu(6)-F coordination mode, are compared with those of the parent complex with a vacant Cu-6-cage.
First author: Mehmood, U, New 1,3,4-Oxadiazole Based Photosensitizers for Dye Sensitized Solarg Cells, INTERNATIONAL JOURNAL OF PHOTOENERGY, 44, 20685, (2015)
Abstract: 1,3,4-Oxadiazole based photosensitizers with biphenyl, naphthalene, anthracene, and triphenylamine as the electron-donating moiety were synthesized for solar cell applications. In these photosensitizers, cyano groups were introduced as the electron acceptor and the anchor group because of their high electron-withdrawing ability and strong bonding to the semiconductor. Oxadiazole isomers were used as the pi-conjugation system, which bridges the donor-acceptor systems. The electrochemical and optical properties of the sensitizers were investigated both in their native form and upon incorporation into dye sensitized solar cells. The results of UV-visible absorption spectroscopy, electrochemical impedance spectroscopic measurements, and photocurrent voltage characteristics indicate that 1,3,4-oxadiazole pi-spacer with the anthracene moiety has the highest efficiency of 2.58%. Density functional theory was employed to optimize the structures of the sensitizers and the TiO2 cluster.
First author: Du, W, Rational modifications on ruthenium terpyridine sensitizers with largeg J(sc) for dye-sensitized solar cells: combined DFT and relativisticg TDDFT studies, RSC ADVANCES, 5, 100169, (2015)
Abstract: In this work, we designed a series of ruthenium sensitizers DX2-DX5 derived from a phosphinecoordinated ruthenium sensitizer DX1 with a surprisingly high short-circuit photocurrent density (J(sc)) of 26.8 mA cm(-2) for dye sensitized solar cells (DSSCs), with the aim of enhancing the light harvesting ability in the near-infrared (NIR) region and further increasing the J(sc). Density functional theory (DFT) and relativistic time-dependent DFT calculations have been performed to evaluate the optical and photovoltaic properties of these Ru dyes, taking the effect of spin-orbit coupling (SOC) into consideration. The intrinsic causes for varied J(sc) and open-circuit photovoltage (V-oc) have been systematically discussed through investigating the light harvesting efficiency, electron injection driving force, dye regeneration driving force, electronic coupling and conduction band energy shift. The calculated results reveal that the designed DX5 has increased light harvesting efficiency in the NIR region and a higher conduction band energy shift compared with other sensitizers. That is, DX5 may have improved J(sc) and V-oc, which makes DX5 serve as a promising sensitizer for future DSSC applications.
First author: Busch, M, Linear scaling relationships and volcano plots in homogeneous catalysisg – revisiting the Suzuki reaction, CHEMICAL SCIENCE, 6, 6754, (2015)
Abstract: Linear free energy scaling relationships and volcano plots are common tools used to identify potential heterogeneous catalysts for myriad applications. Despite the striking simplicity and predictive power of volcano plots, they remain unknown in homogeneous catalysis. Here, we construct volcano plots to analyze a prototypical reaction from homogeneous catalysis, the Suzuki cross-coupling of olefins. Volcano plots succeed both in discriminating amongst different catalysts and reproducing experimentally known trends, which serves as validation of the model for this proof-of-principle example. These findings indicate that the combination of linear scaling relationships and volcano plots could serve as a valuable methodology for identifying homogeneous catalysts possessing a desired activity through a priori computational screening.
First author: Gendron, F, Single-ion 4f element magnetism: an ab-initio look at Ln(COT)(2)(-), DALTON TRANSACTIONS, 44, 19886, (2015)
Abstract: The electron densities associated with the Ln 4f shell, and spin and orbital magnetizations (magnetic moment densities'), are investigated for the Ln(COT)(2)(-) series. The densities are obtained from ab-initio calculations including spin-orbit coupling. For Ln = Ce, Pr the magnetizations are also derived from crystal field models and shown to agree with the ab-initio results. Analysis of magnetizations from ab-initio calculations may be useful in assisting research on single molecule magnets.
First author: Chadwick, FM, Group 9 bimetallic carbonyl permethylpentalene complexes, DALTON TRANSACTIONS, 44, 20147, (2015)
Abstract: We describe the synthesis, structure and bonding of the first iridium and rhodium permethylpentalene complexes, syn-[M(CO)(2)](2)(mu:eta(5):eta(5)-Pn*) (M = Rh, Ir). In fact, [Ir(CO)(2)](2)(mu:eta(5):eta(5)-Pn*) is the first iridium pentalene complex. An interesting preference for the isolation of the sterically more demanding syn-isomer is observed and substantiated by DFT analysis. Upon photolysis, the rhodium analogue yields an unusual tetrameric species Rh-4(CO)(6)(mu:eta(3):eta(5)-Pn*)(2) with bridging carbonyls and Rh-Rh bonds, which has been characterised by single crystal X-ray diffraction and by solution NMR spectroscopy.
First author: Ciancaleoni, G, Charge-displacement analysis as a tool to study chalcogen bonded adductsg and predict their association constants in solution, DALTON TRANSACTIONS, 44, 20168, (2015)
Abstract: The secondary interaction between a polarized chalcogen atom and different Lewis bases, either anionic or neutral, has been studied by charge displacement analysis. Using charge displacement analysis, the charge rearrangement in the adduct upon the formation of the interaction has been quantified and described in great detail. By comparing the theoretical results with the experimental association constants, two linear correlations can be found for anionic and neutral bases. Such correlations can be used to reliably predict the association constants of adducts for which experimental data are not available yet.
First author: Borocci, S, Complexes of the noble gases with H3O+: a theoretical investigation ofg Ng(H3O+) (Ng = He-Xe), EUROPEAN JOURNAL OF MASS SPECTROMETRY, 21, 171, (2015)
Abstract: The geometries, harmonic vibrational frequencies, and binding energies (BEs) of the Ng(H3O+) complexes (Ng = He-Xe) were investigated at the coupled cluster level of theory, and their bonding situation was assayed by various methods of bonding analysis. The effects of Ng on H3O+ progressively increase from He to Xe, and only He can be regarded as an essentially "innocent" ligand. The BEs also increase in the same periodic order, and are by far dominated by the "noncovalent" ion-induced dipole interaction arising from the H3O+-induced polarization of Ng. For Ne, Ar, Kr, and Xe, this term has a larger contribution from the p orbital lying on the bond axis, and two smaller contributions from the p orbitals perpendicular to the bond axis. For the heaviest, Ar(H3O+), Kr(H3O+), and Xe(H3O+), the BE also has a "covalent" component, which is ascribed to the relatively-appreciable charge transfer from Ng to H3O+.
First author: Ortolan, AO, Role of the cation formal charge in cation-pi interaction. A surveyg involving the [2.2.2]paracyclophane host from relativistic DFTg calculations, NEW JOURNAL OF CHEMISTRY, 39, 9963, (2015)
Abstract: The foie of the metal formal charge in the cation-pi interactions has been evaluated with relativistic DFT methods involving a versatile pi-cryptating structure, namely [2.2.2]paracyclophane. Our study focuses on experimentally characterized [([2.2.21pCp)M](n+) systems with M = Ag+ and Sn2+ and their Cd2+ and In counterparts, which exhibit 5s(0)5p(0) and 5s(2)5p(0) electron configurations. The acceptor capabilities increase when the metaI charges go from 1+ to 2+, resulting in a large stabilization of the interaction. For the studied 5s(0)5p(0) cations Ag+ and Cd2+, the most stable conformation namely [(eta(2):eta(2):eta(2)-[2.2.2]pCp)M](n+), the electrostatic contribution is more favorable by -9.3 kcal mol(-1), whereas the Delta E-Orb contribution increases by -151.6 kcal mol(-1) towards a more favourable situation in the 2+ counterpart. Similarly in the 5s(2)5p(0) cationic group, the isoelectronic Sn2+ and In systems depict variation of the electrostatic and orbital terms, with a considerable decrease of the stabilizing Delta E-Orb contribution, and in a lesser amount the Delta E-Elstat term. Thus, the variation of the interaction energy between the M+ and M2+ isoelectronic counterparts can be ascribed mainly to the variation of the Delta E-Orb term, leading to a more covalent character of the interaction retaining a similar bonding scheme.
First author: Antoniou, P, Vibrational control of electron-transfer reactions: a feasibility studyg for the fast coherent transfer regime, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 30854, (2015)
Abstract: Molecular vibrations and electron-vibrational interactions are central to the control of biomolecular electron and energy-transfer rates. The vibrational control of molecular electron-transfer reactions by infrared pulses may enable the precise probing of electronic-vibrational interactions and of their roles in determining electron-transfer mechanisms. This type of electron-transfer rate control is advantageous because it does not alter the electronic state of the molecular electron-transfer system or irreversibly change its molecular structure. For bridge-mediated electron-transfer reactions, infrared (vibrational) excitation of the bridge linking the electron donor to the electron acceptor was suggested as being capable of influencing the electron-transfer rate by modulating the bridge-mediated donor-to-acceptor electronic coupling. This kind of electron-transfer experiment has been realized, demonstrating that bridge-mediated electron-transfer rates can be changed by exciting vibrational modes of the bridge. Here, we use simple models and ab initio computations to explore the physical constraints on one's ability to vibrationally perturb electron-transfer rates using infrared excitation. These constraints stem from the nature of molecular vibrational spectra, the strengths of the electron-vibrational coupling, and the interaction between molecular vibrations and infrared radiation. With these constraints in mind, we suggest parameter regimes and molecular architectures that may enhance the vibrational control of electron transfer for fast coherent electron-transfer reactions.
First author: Novkovic, L, Synthesis of endoperoxides by domino reactions of ketones and molecularg oxygen, RSC ADVANCES, 5, 99577, (2015)
Abstract: Domino reactions of ketones with molecular oxygen in the presence of potassium hydroxide and potassium t-butoxide afford cyclic hydroperoxy acetals (3,5-dihydroxy-1,2-dioxanes). Mixed endoperoxides can also be obtained in a three-component reaction of two ketones and oxygen.
First author: George, A, Atom precise platinum-thiol crowns, NANOSCALE, 7, 19448, (2015)
Abstract: Ligand stabilized water soluble Pt nanoclusters were synthesized and characterized through electrospray ionization mass spectrometry. Glutathione was used as the ligand, and Pt-5(SG)(10), and Pt-6(SG)(12) clusters were synthesized. Theoretical investigations found that these clusters do not possess a metal core, but rather are most stable in a ring structure. The clusters are stabilized through the thiol ligands forming a square planar structure around each Pt atom to form a ring. The structural elucidation was confirmed through UV/Vis and IR spectroscopy.
First author: Zanetti-Polzi, L, A few key residues determine the high redox potential shift in azuring mutants, ORGANIC & BIOMOLECULAR CHEMISTRY, 13, 11003, (2015)
Abstract: The wide range of variability of the reduction potential (E-0) of blue-copper proteins has been the subject of a large number of studies in the past several years. In particular, a series of azurin mutants have been recently rationally designed tuning E-0 over a very broad range (700 mV) without significantly altering the redox-active site [Marshall et al., Nature, 2009, 462, 113]. This clearly suggests that interactions outside the primary coordination sphere are relevant to determine E-0 in cupredoxins. However, the molecular determinants of the redox potential variability are still undisclosed. Here, by means of atomistic molecular dynamics simulations and hybrid quantum/classical calculations, the mechanisms that determine the E-0 shift of two azurin mutants with high potential shifts are unravelled. The reduction potentials of native azurin and of the mutants are calculated obtaining results in good agreement with the experiments. The analysis of the simulations reveals that only a small number of residues (including non-mutated ones) are relevant in determining the experimentally observed E-0 variation via site-specific, but diverse, mechanisms. These findings open the path to the rational design of new azurin mutants with different E-0.
First author: Gao, X, Impacts of terminal modification of [Ru(phen)(2)dppz](2+) on theg luminescence properties: a theoretical study, DALTON TRANSACTIONS, 44, 19264, (2015)
Abstract: Ru(phen)(2)dppz](2+) and other closely related ruthenium(II) complexes containing pi-extended ligands were found to be non or weakly emissive in water, while exhibiting significant luminescence intensity growth when bound to DNA, however, a satisfactory interpretation has not been provided on this "light switch" mechanism. In the present study, we investigated the vertical transitions and triplet excited states of [Ru(phen)(2)dppz](2+) (1), [Ru(phen)(2)dppzi](2+) (2) and [Ru(phen)(2)dppz-idzo](2+) (3) in the gas phase and aqueous solution, through time dependent-density functional theory (TDDFT). Based on the optimized (MLCT)-M-3 and (LLCT)-L-3 structures and energies, we found that the (MLCT)-M-3 state might be responsible for the emissions of the complexes. Interesting connections between the singlet vertical transitions and the luminescence properties were noticed. Through ZORA-TDDFT calculation with perturbative SOC, we evaluated the intersystem crossing between the lowest singlet excited state, and both (MLCT)-M-3 state and (LLCT)-L-3 state, which gave a reasonable explanation for the luminescence properties of these complexes.
First author: Costuas, K, Combined theoretical and time-resolved photoluminescence investigationsg of [(Mo6Br8Br6a)-Br-i](2-) metal cluster units: evidence of dualg emission, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 28574, (2015)
Abstract: The combined time-resolved photoluminescence (PL) and theoretical study performed on luminescent [(Mo6Br8Br6a)-Br-i](2-)-based systems unambiguously shows that their NIR-luminescence is due to at least two emissive states. By quantum chemical studies, we show for the first time that important geometrical relaxations occur at the triplet states either by the outstretching of an apex away from the square plane of the Mo-6 octahedron or by the elongation of one Mo-Mo bond. Experimental PL measurements demonstrate that the external environment (counter-ions, crystal packing) of the cluster has a noticeable impact on its relaxation processes. Temperature and excitation wavelength dependence of the two components of the luminescence spectra is representative of multiple competitive de-excitation processes in contradiction with Kasha's rule. Our results also demonstrate that the relaxation processes before and after emission can be tracked via fast time-resolved spectroscopy. They also show that the surroundings of the luminescent cluster unit and the excitation wavelength could be modulated for target applications.
First author: Yi, WJ, Isomers of organic semiconductors based on dithienothiophenes: theg effect of sulphur atoms positions on the intermolecular interactions andg field-effect performances, JOURNAL OF MATERIALS CHEMISTRY C, 3, 10856, (2015)
Abstract: 2,5-Distyryl-dithieno[2,3-b: 2′,3′-d] thiophene (DEP-bt-DTT), an isomer of 2,5-distyryl-dithieno [2,3-b:3′,2′-d]-thiophene (DEP-bb-DTT) and 2,5-distyryl-dithieno[3,2-b:2′,3′-d] thiophene (DEP-tt-DTT), was synthesized. Organic field-effect transistors (OFETs) based on these three isomers were fabricated. The structure cell parameters and the formation of intermolecular interactions in their single crystals show regular change when the positions of sulphur atoms vary from top-bottom-top in DEP-tt-DTT to bottom-bottom-top in DEP-bt-DTT, then to bottom-bottom-bottom in DEP-bb-DTT. Combining the results of theoretical calculations and OFET performances, it reveals that: (1) the positions of sulphur atoms determine the contribution extent of sulphur atoms to the molecular conjugation and the formation of intermolecular interactions; (2) the existence of the intermolecular interactions, especially for S-pi, benefits for the charge transport; (3) the field-effect mobility (mu) increases with increasing of the sulphur atom contribution to the molecular conjugation.
First author: Majid, A, Ti-Ga-V-N complexes in GaN: a new prospect of carrier mediatedg ferromagnetism, RSC ADVANCES, 5, 87437, (2015)
Abstract: First principle investigations exploring the effects of nitrogen vacancies on ferromagnetism in Ti doped wurtzite GaN are reported. The presence of nitrogen vacancies demonstrated no noticeable effect in the case of pure GaN but exhibited ferromagnetism in the case of Ti doped GaN. The magnetic moment however ceased upon doubling the concentration of dopant and vacancies in the host which points towards possible antiferromagnetic coupling. The conventional double exchange ordering observed in the case of the vacancy-added Ti:GaN switched to a carrier mediated exchange for the Ti-Ga-V-N complex in Ti:GaN. For Ti doped GaN, the energy difference calculated with and without N vacancies is found to be relatively smaller than that of other 3d transition metal (Cr, Mn, Fe, Co, Ni, Cu) doped GaN. The results calculated for different configurations to explore the effects of nitrogen vacancies on the electronic and magnetic properties of Ti:GaN are discussed in detail.
First author: Novoa, N, Four-coordinate nickel(II) and copper(II) complex based ONO tridentateg Schiff base ligands: synthesis, molecular structure, electrochemical,g linear and nonlinear properties, and computational study, DALTON TRANSACTIONS, 44, 18019, (2015)
Abstract: We report the synthesis, characterization, crystal structures, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations of nickel(II) and copper(II) complex based ONO tridentate Schiff base ligands: two mononuclear compounds, [Ni(An-ONO)(NC5H5)] (5) and [Cu(An-ONO)(4-NC5H4C(CH3)(3))] (6), and two heterobimetallic species, [M(Fc-ONO)(NC5H5)] (M = Ni, 7; Cu, 8), where An-ONOH2 (3) and Fc-ONOH2 (4) are the 1 : 1 condensation products of 2-aminophenol and p-anisoylacetone and ferrocenoylacetone, respectively. These compounds were characterised by microanalysis, FT-IR and X-ray crystallography in the solid state and in solution by UV-vis and H-1 and C-13 NMR spectroscopy. The crystal structures of 3-5, 7 and 8 have been determined and show for Schiff base complexes 5, 7 and 8 a four-coordinated square-planar environment for nickel and copper ions. The electrochemical behavior of all derivatives 3-8 was investigated by cyclic voltammetry in dichloromethane, and discussed on the basis of DFT-computed electronic structures of the neutral and oxidized forms of the compounds. The second-order NLO responses of 3-8 have been determined by harmonic light scattering measurements using a 10(-2) M solution of dichloromethane and working with a 1.91 mu m incident wavelength, giving rather high beta(1.91) values of 350 and 290 x 10(-30) esu for the mononuclear species 5 and 6, respectively. The assignment and the nature of the electronic transitions observed in the UV-vis spectra were analyzed using time-dependent (TD) DFT calculations. They are dominated by LMCT, MLCT and pi-pi* transitions.
First author: Zhang, WT, The electronic structures and photophysical properties of platinumg complexes with (CNN)-N-Lambda-N-Lambda ligands: the influence of theg carborane substituent, DALTON TRANSACTIONS, 44, 18130, (2015)
Abstract: Carboranes have attracted increasing interest in the scientific community due to their remarkable structures and strong electron-withdrawing abilities. In this article, four platinum complexes [((CNN)-N-Lambda-N-Lambda)PtCgCPh](1), [((CNN)-N-Lambda-N-Lambda)PtCgC-TPA](2), [((CNN)-N-Lambda-N-Lambda)PtCgC-TAB](3), [((CNN)-N-Lambda-N-Lambda)PtCgC-CB](4) (where TPA = triphenylamine, TAB = triarylboryl, CB = o-carborane) have been calculated via density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods to mainly explore the influence of carborane substituents on electronic structures, photophysical properties and radiative decay processes. The calculated results reveal that 2 with electron-donating triphenylamine has a low radiative decay rate constant and a red-shifted emission band, but 3 and 4 containing electron-withdrawing triarylboryl and o-carborane exhibit the opposite properties, especially 4 is supposed to have the highest phosphorescence quantum yield with the smallest nonradiative decay rate constant. These findings successfully illustrated the structure-property relationship and the designed complex 4 with carborane can serve as a highly efficient phosphorescent material in the future.
First author: Kerber, RN, Grafting trimethylaluminum and its halogen derivatives on silica:g general trends for Al-27 SS-NMR response from first principlesg calculations, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 26937, (2015)
Abstract: Al-27 NMR is the method of choice for studying grafted Al species on a large area solid support, such as co-catalysts for alpha-olefin oligomerization involving mesoporous silica materials. Here, we show how to interpret the Al-27 solid-state NMR spectrum and parameters for various types of Al monomeric and dimeric alkyl and halogen compounds grafted on silica, based on the trends obtained from first-principles calculations. Since most alkylaluminum species tend to form dimers in the gas phase, we chose as prototypes both the AlMe3 monomer and the Al2Me6 dimer. On top of that the influence of chlorine substituents on the NMR parameters is explored considering all possible isomers. There are two main effects on the Al NMR parameters observed in the case of monomers: (i) the larger pi-donating character of the ligands (from Me to Cl for example) leads to a decrease of the quadrupolar coupling constant C-Q and (ii) the larger sigma-attracting character of the ligand (from Cl to F for example) yields an upfield variation of the Al chemical shift delta(ISO) while in contrast C-Q is increased. The same is true also in the case of dimeric species, with an additional specific effect. By Al-27 solid state NMR we can differentiate clearly between terminal and bridge positions for the substituents. The reason for this phenomenon is explained in terms of different natural localized MO (NLMO) contributions to the C-Q parameter. This aspect is important because the surface sites for this type of system are expected to be mostly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands.
First author: Stuart, D, The effect of nitrido, azide, and nitrosyl ligands on magnetizationg densities and magnetic properties of iridium PNP pincer-type complexes, RSC ADVANCES, 5, 84311, (2015)
Abstract: We present a systematic theoretical study of electronic structures, magnetization densities, and magnetic properties of iridium PNP pincer-type complexes containing non-innocent nitrido, azide, and nitrosyl ligands. Specifically, the quality and accuracy of density functional theory (DFT) in predicting magnetization densities obtained from various approximate exchange-correlation functionals is assessed by comparing them to complete active space self-consistent field (CASSCF) reference distributions. Our analysis points to qualitative differences in DFT magnetization densities at the iridium metal center and the pincer ligand backbone compared to CASSCF reference data when the non-innocent ligands are changed from nitrido, to azide, to nitrosyl. These observations are reflected in large differences in hyperfine couplings calculated for the iridium metal center.
First author: Wang, CZ, Actinide (An = Th-Pu) dimetallocenes: promising candidates forg metal-metal multiple bonds, DALTON TRANSACTIONS, 44, 17045, (2015)
Abstract: Synthesis of complexes with direct actinide-actinide (An-An) bonding is an experimental 'holy grail' in actinide chemistry. In this work, a series of actinide dimetallocenes An(2)Cp(2)* (Cp* = C-5(CH3)(5), An = Th-Pu) with An-An multiple bonds have been systematically investigated using quantum chemical calculations. The coaxial Cp*-An-An-Cp* structures are found to be the most stable species for all the dimetallocenes. A Th-Th triple bond is predicted in the Th2Cp2* complex, and the calculated An-An bond orders decrease across the actinide series from Pa to Pu. The covalent character of the An-An bonds is analyzed by using natural bond orbitals (NBO), molecular orbitals (MO), the quantum theory of atoms in molecules (QTAIM), and electron density difference (EDD). While Th 6d orbitals dominate the Th-Th bonds in Th2Cp2*, the An 6d-orbital characters decrease and 5f-orbital characters increase for complexes from Pa2Cp2* to Pu2Cp2*. All these actinide dimetallocenes are stable in the gas phase relative to the AnCp* reference at room temperature. Based on the reactions of AnCp(2)* and An, Th2Cp2*, Pa2Cp2* and possibly also U2Cp2* should be accessible as isolated molecules under suitable synthetic conditions. Our results shed light on the molecular design of ligands for stabilizing actinide-actinide multiple bonds.
First author: Jagadeesan, R, The nature of Pd-carbene and Pd-halogen bonds in (bisNHC)PdX2 typeg catalysts: insights from density functional theory, RSC ADVANCES, 5, 80661, (2015)
Abstract: Methylene bridged palladium biscarbene halide complexes have proven to be excellent catalysts in cross coupling reactions and in activation of alkanes. These types of complexes are widely used in decomposition and reductive elimination reactions because of their more stable carbene-Pd bond. The electronic structure and bonding of such methylene bridged palladium biscarbene complexes (LnPdX(2)) (Ln = NHC) have been investigated using density functional theory. The calculated results reveal that the nature of the substituents as well as the coordinating halide ion determine the strength of the Pd-C-carbene and Pd-X bonds. These two bonds can be fine-tuned to achieve better catalytic activity through proper substituents. In effect, this can be done by making the Pd-C-carbene bond much stronger through sigma-donation and pi-back donation and also by making the Pd-X bond weaker by choosing a suitable halide (X).
First author: Filippi, A, Electronic structure and conformational flexibility of D-cycloserine, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 25845, (2015)
Abstract: The first comprehensive investigation of the effect of conformational flexibility of gaseous D-cycloserine on the valence and core electronic structures is reported here. The seven most stable conformers among the twelve structures calculated at the MP2/6-311++G** level of theory were assumed to properly describe the properties of the investigated compound. Taking into account the contribution of these isomers, the valence photoelectron spectrum (UPS) was simulated by the Outer Valence Green's Function (OVGF) method. A different sensitivity towards the conformational flexibility of the outermost photoelectron bands was exhibited in the simulated spectrum. The comparison of the theoretical UPS with the experimental one allowed a detailed assignment of the outermost valence spectral region. The composition and bonding properties of the relevant MOs of the most stable conformers were analyzed in terms of leading Natural Bond Orbital (NBO) contributions to the HF/6-311++G** canonical MOs. The C1s, N1s, and O1s photoelectron spectra (XPS) were theoretically simulated by calculating the vertical Ionization Energies (IEs) of the relevant conformers using the DSCF approach. The different IE chemical shift spread of the XPS components associated with various conformers, which is expected to affect the experimental spectra, could be evaluated by simulated XPS, thus providing a new insight into the core electronic structure. The comparison of the theoretical results with the experimental ones unraveled that the atomic XPS components are not mixed by conformational flexibility of D-cycloserine, and that the specific vibronic structure of different spectral components should play a crucial role in determining different relative intensities and band shapes observed in the experiment.
First author: Mendizabal, F, Theoretical study on interactions of fluorinated organomercurials withg arene and gold fragments, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 26417, (2015)
Abstract: The electronic structure and spectroscopic properties of [Hg(C6F5)(2)](2)-{L}, [Hg-3(o-C6F4)(3)](2)center dot{L} (L = naphthalene, biphenyl, fluorene) and [Hg-3(o-C6F4)(3)]{Au-3(mu-C(OEt)=NC6H4CH3)(3)}(n) (n = 1, 2) adducts were studied at the HF, MP2, SCS-MP2, DFT and DFT-D3 levels. The intermolecular interactions among the fragments were analyzed using the levels of calculations proposed. The energy decomposition analysis at the TPSS-D3 level was used to define the dominant components of the interaction. The van der Waals interactions between mercury and arene (Hg-arene) were found to be the main short-range stability contribution in the [Hg(C6F5)(2)](2)-{L} and [Hg-3(o-C6F4)(3)](2)center dot{L} complexes. At the MP2, SCS-MP2 and DFT-D3 levels, equilibrium Hg-C distances are between 360 and 310 pm. The pair-wise energies were found to be between 18.0 and 6.0 kJ mol(-1). In the [Hg-3(o-C6F4)(3)]{Au-3(mu-C(OEt)=NC6H4CH3)(3)}(n) (n = 1, 2) complexes the metallophilic intermolecular interaction is Hg-Au. Pair-wise energies of 85.7, 39.4, 78.1 and 57.9 kJ mol(-1) were found at the MP2, SCS-MP2, TPSS-D3 and PBE-D3 levels using the [Hg3(o-C6F4) 3]{ Au-3(mu-C(OEt)=NC6H4CH3)(3)} model. The same trend is maintained for the [Hg-3(o-C6F4)(3)]{Au-3(mu-C(OEt)=NC6H4CH3)(3)}(2) model: 73.4, 29.3, 70.6 and 61.3 kJ mol(-1) by MP2, SCS-MP2, TPSS-D3 and PBE-D3, respectively. The absorption spectra of these complexes were calculated using the single excitation time-dependent method at the TPSS-D3 level to validate the models against the experimental data.
First author: Deb, AKS, Unanticipated favoured adsorption affinity of Th(IV) ions towardsg bidentate carboxylate functionalized carbon nanotubes (CNT-COOH) overg tridentate diglycolamic acid functionalized CNT: density functionalg theoretical investigation, RSC ADVANCES, 5, 80076, (2015)
Abstract: The hybrid B3LYP density functional and TZVP basis set in conjunction with COSMO solvation approach have been used successfully to predict the free energy of adsorption for Th4+ ions with pristine CNTs, oxidized CNTs (CNT-COOH) and diglycolamic acid functionalized CNTs (CNT-DGA). Experimentally reported values of adsorption capacities of Th4+ by the above three types of CNT indicate that CNT-COOH has the strongest binding with Th4+, whereas p-CNT has the lowest; CNT-DGA shows less adsorption than CNT-COOH, although the former has tridentate ligands on CNTs' surfaces. This experimental observation has been demonstrated by DFT theoretical studies: gas phase calculation does not match with the above experimental fact, whereas, solvent phase calculation in the presence of nitrate ions, a more realistic approach, is able to explain. Free energy of complexation between Th4+ and CNT-COOH is higher than that of CNT-DGA in all available models of complexation reaction viz. bare Th4+ in aqueous nitrate medium, octahydrated Th4+ in nitrate and thorium nitrate ion pair in aqueous solution. The experimental fact that the presence of oxidized fullerene C-60 enhances the Th4+ adsorption by oxidized CNT has also been theoretically corroborated as oxidized C-60 has a quite high binding energy for Th4+. Present computational calculation in the search for the best nano carbon based Th4+ adsorbent parallel with experimental verification might be helpful for the design of effective nanomaterials to be used in the treatment of radioactive liquid waste.
First author: Safin, DA, Luminescent mononuclear mixed ligand complexes of copper(I) withg 5-phenyl-2,2 '-bipyridine and triphenylphosphine, DALTON TRANSACTIONS, 44, 16824, (2015)
Abstract: Reaction of 5-phenyl-2,2′-bipyridine (L) with a mixture of CuI or [Cu(CH3CN)(4)]BF4 and PPh3 leads to mononuclear heteroleptic complexes [CuL(PPh3)I] (1) and [CuL(PPh3)(2)]BF4 (2). According to X-ray diffraction, L crystallizes in the monoclinic space group P2(1)/n, exhibiting a disorder over four orientations. Complexes 1 and 2 crystallize in the monoclinic space groups P2(1)/c and P2(1), respectively. 1 comprises a discrete neutral molecule, while 2 has an ionic structure containing [CuL(PPh3)(2)](+) and BF4-. Both structures reveal that each tetracoordinated copper(I) atom is linked to two nitrogen atoms of L, one iodide and one PPh3 in the structure of 1, or two PPh3 in the structure of 2 with the formation of a distorted tetrahedral coordination core. The structure of 2 is additionally stabilized by a weak intramolecular pi center dot center dot center dot pi stacking interaction formed between two adjacent phenyl rings of two PPh3 ligands. Hirshfeld surface analysis showed that the structures of both complexes are mainly characterized by H center dot center dot center dot H and C center dot center dot center dot H contacts as well as by I center dot center dot center dot H in the structure of 1 and F center dot center dot center dot H in the structure of 2. The 2D fingerprint plots of two different molecules in the structure of L showed that both molecules exhibit contacts for p center dot center dot center dot p stacking interactions. The factors important for the stability of 1 and 2 were further quantitatively and qualitatively characterized by the charge and energy decomposition method ETS-NOCV. According to diffuse reflectance spectroscopy in the solid state, free L exhibits bands exclusively in the UV region, while the spectra of 1 and 2 also contain bands in the visible range up to about 500 and 600 nm. All three compounds were found to be emissive in the solid state. DFT calculations have shown that, while emission of L is due to the ligand-centered pi ->pi* transition, luminescence of 1 and 2 was assigned to a (M + X) LCT and MLCT excited states, respectively.
First author: Bulloni, C, Effect of Ca2+ codoping on the Eu2+ luminescence properties in theg Sr2Si5N8 host lattice: a theoretical approach, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 24925, (2015)
Abstract: Here we report a theoretical analysis of the luminescence properties of Sr2Si5N8 host lattices codoped with Ca2+ and Eu2+. These systems have been first synthesized by Li et al. [J. Solid State Chem., 2008, 181, 515], who have found that Ca2+ doping provokes a red-shifting of the emission peak of Eu2+, from 620 nm to 643 nm. However, the mechanism that drives this shift is still unclear from experimental data. Based on density functional theory and ligand field analysis, we study the structure, stability, and emission properties of Eu2+ embedded in the (Sr1-xCax)(2)Si5N8 host lattice. Our results provide a full explanation of the experimental data and the methodology could constitute a valuable tool for the design of phosphors with tunable emission spectra.
First author: Alkan, F, Chemical-shift tensors of heavy nuclei in network solids: a DFT/ZORAg investigation of Pb-207 chemical-shift tensors using the bond-valenceg method, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 25014, (2015)
Abstract: Cluster models are used in calculation of Pb-207 NMR magnetic-shielding parameters of alpha-PbO, beta-PbO, Pb3O4, Pb2SnO4, PbF2, PbCl2, PbBr2, PbClOH, PbBrOH, PbIOH, PbSiO3, and Pb-3(PO4)(2). We examine the effects of cluster size, method of termination of the cluster, charge on the cluster, introduction of exact exchange, and relativistic effects on calculation of magnetic-shielding tensors with density functional theory. Proper termination of the cluster for a network solid, including approximations such as compensation of charge by the bond-valence (BV) method, is essential to provide results that agree with experiment. The inclusion of relativistic effects at the spin-orbit level for such heavy nuclei is an essential factor in achieving agreement with experiment.
First author: Zhang, XY, Anisotropic electron-transfer mobilities ing diethynyl-indenofluorene-dione crystals as high-performance n-typeg organic semiconductor materials: remarkable enhancement by varyingg substituents, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 25463, (2015)
Abstract: In this study, the electron-transfer properties of alkynylated indenofluorene-diones with various substituents (SiMe3, SiPr3, and SiPh3) that function as n-type organic semiconductors were comparatively investigated at the first-principles DFT level based on the Marcus-Hush theory. The reorganization energies are calculated by the adiabatic potential-energy surface method, and the coupling terms are evaluated through a direct adiabatic model. The maximum value of the electron-transfer mobility of SiPr3 is 0.485 cm(2) V-1 s(-1), which appears at the orientation angle of the conducting channel on the reference plane a-b near to 172 degrees/352 degrees. The predicted maximum electron mobility value of SiPr3 is nearly 26 times larger than that of SiPh3. This may be attributed to the largest number of intermolecular pi-pi interactions. In addition, the mobilities in all three crystals show remarkable anisotropic behavior. The calculated results indicate that SiPr3 could be an ideal candidate as a high-performance n-type organic semiconductor material. Our investigations not only give us an opportunity to completely understand the charge transport mechanisms, but also provide guidelines for designing materials for electronic applications.
First author: Stojanovic, M, A theoretical study on borenium ion affinities toward ammonia,g formaldehyde and chloride anions, RSC ADVANCES, 5, 75895, (2015)
Abstract: Various borenium ion affinities toward three ligands (L' = NH3, HCHO and Cl-) have been evaluated by DFT calculations in the gas-phase and in solvent (CH2Cl2). The gas-phase results have been rationalized on the basis of quantitative decomposition of the total binding energy into contributions from electrostatic, orbital, dispersion and Pauli interactions, and energy needed to deform the interacting fragments from their optimal geometry to that they adopt in an adduct. Twenty six borenium cations, differing in the type of the two R/R' substituents covalently bound to the boron atom and the neutral stabilizing ligand L, have been examined. With a few exceptions, the most important stabilizing interaction is electrostatic, more pronounced in the case of the charged ligand Cl-. Next come orbital interactions, involving the coordinate covalent bond formation, other charge transfer interactions between the cation and ligand, and polarization. Dispersion forces provide the smallest attraction, except in four complexes with long B-L' distances. We present how substituent (R/R')/ligand (L) variations affect binding enthalpies (Delta H)/energies (Delta E). Our results also show that the observed trend in the magnitudes of Delta Hs/Delta Es represents an interplay of the above mentioned (de) stabilizing energies, and can be explained by consideration of the boron-ligand distance and all charge/orbital interactions, rather than partial ones involving boron and ligand L'. Under solvent conditions, the Cl- affinities are drastically reduced and made very similar to NH3 affinities, but still larger than HCHO affinities.
First author: Manzetti, S, Intriguing properties of unusual silicon nanocrystals, RSC ADVANCES, 5, 78192, (2015)
Abstract: Solar cell technologies are highly dependent on silicon materials and novel nanoclusters with optimal electronic properties. Based on a recent study on ultrastable silicon nanoclusters, an analysis of the effects of modifications of those nanocrystals by carboxylation, amidation, hydroxylation and halogenation has been performed using quantum mechanical methods of study. Here we report the gaps, electronic structures, absorption spectra, and effects on the charge-transfer potential of a collection of modified silicon nanoclusters. The results show that the pristine silicon clusters retain the highest charge-transfer properties and that halogenation impacts on the charge-transfer effects in a proportional fashion to the electronegativity of the employed halogens. Modification with organic molecules does not improve charge-transfer properties, and gives instead the highest reduction of charge-transfer potentials of the silicon clusters. The effects of the modification have also been studied in context with the orbital configurations through wave function analysis, which reveals that the electrostatic properties of the nanoclusters are mainly represented by a significant polarization of the electrostatic energy between the peripheral regions of the clusters and their core, a feature particularly well-preserved in the pristine silicon clusters. Modifying the particles by adding an extra atom at their core shows significant effects on the molecular orbital properties (HOMO/LUMO). However, this modification does not contribute to an actual increase in charge-transfer integrals. The modifications induce, however, interesting effects on the overall configuration of the clusters; i.e., they increase the aromatic character of the inter-atomic bonding pattern. Halogenation has the highest effect on improving aromatic properties for the silicon clusters, where chlorination gives the highest degree of aromaticity. This study introduces valuable electronic data for engineering novel silicon nanoclusters for application in solar cell technologies, computing units, and other fields such as in aerospace engineering.
First author: Sahnoune, H, Fe(dppe)(eta(5)-C5Me5)-Based Phenylalkynyl Complexes Featuring an NO2g End Group: A Theoretical Analysis, AUSTRALIAN JOURNAL OF CHEMISTRY, 68, 1352, (2015)
Abstract: Electronic structures and optical properties of a series of compounds Fe(dppe)(eta(5)-C5Me5){[CgC(1,4-C6H4)](n)NO2} (1-3; n = 1-3, dppe = 1,2-bis(diphenylphosphino) ethane) were investigated with the aid of density functional theory and time-dependent density functional theory computations. The results reveal that the extension of the carbon-rich chain has a moderate influence on the electronic properties of the studied compounds in their ground state, but affects notably their spectroscopic properties, with some unexpected hypsochromic shift of the lower energy absorption bands upon carbon chain lengthening. The appropriate excitations responsible for the low-energy absorption bands involve mainly HOMO-LUMO transitions dominated by important metal-to-ligand charge transfer. A functional including long-range corrections is necessary to reproduce the experimental results.
First author: Pan, S, On the stability of noble gas bound 1-tris(pyrazolyl)borate berylliumg and magnesium complexes, NEW JOURNAL OF CHEMISTRY, 39, 6778, (2015)
Abstract: An in silico study is performed to assess the noble gas (Ng) binding ability of 1-tris(pyrazolyl)borate beryllium and magnesium cationic complexes (TpBe(+) and TpMg(+)). The Be and Mg centers in these complexes are found to bind heavier Ng atoms quite effectively. Both the zero point energy and basis set superposition error corrected dissociation energy values for the bonds between Ar-Rn and metal atoms range within 5.8-10.2 kcal mol(-1) for Be and within 5.2-9.9 kcal mol(-1) for Mg. The dissociation of the Kr-Rn bound analogues of TpBe+ and Ar-Rn bound analogues of TpMg+ into the individual Ng atoms and TpBe+ or TpMg+ complexes is endergonic in nature at room temperature. The remaining lighter Ng bound complexes would be stable at lower temperatures. The nature of Be-Ng or Mg-Ng bonds is explored via Wiberg bond indices computation, atoms-in-molecules and energy decomposition analyses. The degree of covalent character in the Be/Mg-Ng bonds increases gradually in moving from He to its heavier congeners. The Be-Xe/Rn and Mg-Xe/Rn bonds could be categorized as being of the partial covalent type. The contribution from the orbital term is at the maximum towards the total attraction. The magnitude of this term becomes gradually larger from He to Rn, implying a larger degree of covalent character for heavier Ng atoms.
First author: Dai, X, U@C-28: the electronic structure induced by the 32-electron principle, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 23308, (2015)
Abstract: First principles calculations show that the neutral U@C-28 has a (cage)(2) ground state with T-d symmetry instead of the long believed (5f)(1)(cage)(1) ground state with D-2 symmetry. Its 34 valence electrons preferentially obey the 32-electron principle which fills all the s-, p-, d-, and f-type valence shells of the uranium atom. The remaining two valence electrons cannot break the electronic configuration and thus are located on the cage.
First author: Majid, A, Experimental and computational analysis of transition metal ion-dopedg AlInN/GaN thin films, RSC ADVANCES, 5, 72592, (2015)
Abstract: To study ion beam modification on the structural and magnetic properties of metal organic chemical vapor deposition (MOCVD)-grown wurtzite AlInN layers, 200 keV ions of transition metals (TM) Cr, Mn, Co and V were implanted at doses of 5 x 10(14), 5 x 10(15) and 5 x 10(16) cm(-2) into AlInN/GaN thin films. The structural properties of the materials were studied by X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS) techniques. XRD analysis revealed that the GaN-related peak for all the samples remained at its usual Bragg position of 2 theta = 34.56 degrees, whereas there was a shift in the AlInN peak from its position of 2 theta = 35.51 degrees for the as-grown samples. RBS analysis exhibited a shift in the position of the indium-related peak, indicating a migration of indium atoms towards the interface of heterostructures. Moreover, this peak was observed to split into two peaks, which is an indication of the depth-wise redistribution of indium atoms within the material. The measurements of magnetization versus temperature as well as the applied magnetic field performed using a SQUID magnetometer indicated the room temperature ferromagnetism in the materials. The density functional theory based calculations of TM-doped AlInN predicted that the dopant ions would preferably substitute In sites in the alloy.
First author: Yang, TF, Pyromellitic dithioimides: thionation improves air-stability andg electron mobility of N-type organic field-effect transistors, CHEMICAL COMMUNICATIONS, 51, 13772, (2015)
Abstract: Thionation and fluorination of pyromellitic diimides (PyDIs) increased the electron mobility and on/off ratio of the original diimides by two orders of magnitude and improved the threshold voltage and air-stability of diimide compounds.
First author: Sadhu, B, Elucidating the structures and cooperative binding mechanism of cesiumg salts to the multitopic ion-pair receptor through density functionalg theory calculations, DALTON TRANSACTIONS, 44, 15450, (2015)
Abstract: Designing new and innovative receptors for the selective binding of radionuclides is central to nuclear waste management processes. Recently, a new multi-topic ion-pair receptor was reported which binds a variety of cesium salts. Due to the large size of the receptor, quantum chemical calculations on the full ion-pair receptors are restricted, thus the binding mechanisms are not well understood at the molecular level. We have assessed the binding strengths of various cesium salts to the recently synthesized multitopic ion-pair receptor molecule using density functional theory based calculations. Our calculations predict that the binding of cesium salts to the receptor predominantly occurs via the cooperative binding mechanism. Cesium and the anion synergistically assist each other to bind favorably inside the receptor. Energy decomposition analysis on the ion-pair complexes shows that the Cs salts are bound to the receptor mainly through electrostatic interactions with small contribution from covalent interactions for large ionic radius anions. Further, QTAIM analysis characterizes the importance of different inter-molecular interactions between the ions and the receptor inside the ion-pair complexes. The role of the crystallographic solvent molecule contributes significantly by similar to 10 kcal mol(-1) to the overall binding affinities which is quite significant. Further, unlike the recent molecular mechanics (MM) calculations, our calculated binding affinity trends for various Cs ion-pair complexes (CsF, CsCl and CsNO3) are now in excellent agreement with the experimental binding affinity trends.
First author: Andriani, KF, The influence of L ligands on the {RuNO}(6/7) bonding situation ing cis-[Ru(NO)(NO2)L1-4](q) complexes: a theoretical insight, RSC ADVANCES, 5, 69057, (2015)
Abstract: It is regularly claimed that equatorial and axial ligands have a crucial role on the release of nitric oxide in ruthenium nitrosyl complexes. The reactivity of NO is dependent not only on the nature of the coordinated ligands but also on the bonding linkage isomerism that it can be involved. In this work, the interplay between the pi-acceptor character of different L ligands and its effect on the Ru-NO bonding situation in {RuNO}(6) and {RuNO}(7) cores of cis-[Ru(NO)(NO2)L1-4](q) complexes, where L = ammonia, 2,2′-bipyridine, 1,10′-phenanthroline and 1,4,8,11-tetraazacyclotetradecane ligands, is presented. The Ru-NO bonding situation is studied by the energy decomposition analysis of Su and Li, QTAIM and NBO methods. The nitrosyl-isonitrosyl isomerism is also investigated. Results show that complexes containing strong pi-acceptor ligands (2,2'bipyridine and 1,10′-phenanthroline) have their Ru-NO and Ru-ON interactions stabilized prior the NO reduction, while complexes containing weak pi-acceptor ligands (ammonia and 1,4,8,11-tetraazacyclotetradecane) stabilize those interactions after reduction.
First author: Azzopardi, KM, Quantitative assessment of the carbocation/carbene character of theg gold-carbene bond, DALTON TRANSACTIONS, 44, 13999, (2015)
Abstract: The geometric perturbation of the cyclopropyl ring in [LAu(S)](n+) (S = cyclopropyl(methoxy) carbene) complexes has been recently proposed as an indirect experimental probe of the [LAu](n+) electron-donating power, but experimental data are available only for a phosphine ligand [Brooner et al., Chem. Commun., 2014, 50, 2420, L = P(t-Bu)(2)(o-biphenyl)]. We broaden the study through DFT geometry optimization of a large number of systems, including anionic, neutral and cationic ligands. We combine these results with the accurate calculation, through charge displacement analysis, of the Dewar-Chatt-Duncanson components of the Au-carbene bond. The results demonstrate a linear correlation between the distortion of the cyclopropyl ring (Delta d) and the Au -> C pi back-donation, which enables us to confidently estimate back-donation from a simple geometry optimization or, when available, from experimental data such as X-ray crystal structures. Consequently, Delta d can be reliably used to quantitatively determine the position of each system in the continuum between the carbocationic and carbene extremes and the percentage of back-donation that S is able to accept (P-back). In particular, P-back results to be vanishing with cationic ligands, between 18 and 27% with neutral phosphines and carbenes and around 50% with anionic ligands. Finally, we study the effect of the heteroatom on the substrate, showing that the absolute value of the back-donation is enhanced by around 25% when the methoxy is substituted by a methyl group. Despite this, since the absence of the heteroatom also enhances the maximum capacity of the carbene to accept back-donation, the position of the systems in the continuum moves only slightly toward the carbene end.
First author: Safin, DA, Metal ion influences distortion of the ligand in the structure ofg [M{2-MeO(O)CC6H4NHC(S) NP(S)-(OiPr)(2)}(2)] (M = Zn-II, Cd-II)g complexes: a driving force for intermolecular aggregation, DALTON TRANSACTIONS, 44, 14101, (2015)
Abstract: Reaction of the in situ deprotonated N-thiophosphorylated thiourea 2-MeO(O)CC6H4NHC(S) NHP(S)-( OiPr)(2)(HL) with MCl2 (M = Zn-II, Cd-II) in aqueous ethanol leads to complexes of the formula [ML2]. Both compounds crystallise in the triclinic space group P (1) over bar with Z = 2 and the metal cations are found in a tetrahedral S2S'(2) coordination environment formed by the C-S and P-S sulfur atoms. The crystal structures reveal intramolecular N-H center dot center dot center dot O=C hydrogen bonds formed within the 2-MeO(O)CC6H4NH fragments. Both structures are further stabilised by intermolecular pi center dot center dot center dot pi stacking interactions, which are more efficient in [CdL2]. Here, a pronounced dimeric intermolecular aggregate is observed which goes along with a pronounced distortion of the chelate [(S)CNP(S)](-) backbone of the ligand upon coordination to CdII as well as a significantly distorted coordination tetrahedron CdS2S'(2). The aggregation is also reflected in the positive electrospray ionisation (ESI) mass spectrum of the Cd-II complex, which exhibits peaks for the dimeric cations [Cd2L3](+), [Cd2L4 + H](+) and [Cd2L4 + Na](+), while for the Zn-II analogue only monomeric species were observed. Quantum chemical ETS-NOCV (ADF) calculations confirm the higher stability of dimers in [CdL2] compared with [ZnL2]. The pi center dot center dot center dot pi stacking interactions are prodominantly due to dispersion contributions, though the electrostatic and orbital interaction components are also important. QTAIM (ADF) type calculations additionally quantify the covalent and non-covalent interactions in the momomers.
First author: Patel, D, Synthesis and characterisation of halide, separated ion pair, andg hydride cyclopentadienyl iron bis(diphenylphosphino)ethane derivatives, DALTON TRANSACTIONS, 44, 14159, (2015)
Abstract: Treatment of anhydrous FeX2 (X = Cl, Br, I) with one equivalent of bis(diphenylphosphino)ethane (dppe) in refluxing THF afforded analytically pure white (X = Cl), light green (X = Br), and yellow (X = I) [FeX2(dppe)](n) (X = Cl, I; Br, II; I, III). Complexes I-III are excellent synthons from which to prepare a range of cyclopentadienyl derivatives. Specifically, treatment of I-III with alkali metal salts of C5H5 (Cp, series 1), C5Me5 (Cp*, series 2), C5H4SiMe3 (Cp', series 3), C5H3(SiMe3)(2) (Cp ", series 4), and C5H3(Bu-t)(2) (Cp-tt, series 5) afforded [Fe(Cp-dagger)(Cl)(dppe)] 1Cl-5Cl, [Fe(Cp-dagger)(Br)(dppe)] 1Br-5Br, and [Fe(Cp-dagger)(I)(dppe)] 1I-5I (Cp-dagger = Cp, Cp*, Cp', Cp ", or Cptt). Dissolution of 1I-5I in acetonitrile, or treatment of 1Cl-5Cl with Me3SiI in acetonitrile (no halide exchange reactions were observed in other solvents) afforded the separated ion pair complexes [Fe(Cp-dagger)(NCMe)(dppe)][I] 1SIP-5SIP. Attempts to reduce 1Cl-5Cl, 1Br-5Br, and 1I-5I with a variety of reductants (Li-Cs, KC8, Na/Hg) were unsuccessful. Treatment of 1Cl-5Cl with LiAlH4 gave the hydride derivatives [Fe(Cp-dagger)(H)(dppe)] 1H-5H. This report provides a systematic account of reliable methods of preparing these complexes which may find utility in molecular wire and metal-metal bond chemistries. The complexes reported herein have been characterised by X-ray diffraction, NMR, IR, UV/Vis, and Mossbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and elemental analyses, which have enabled us to elucidate the electronic structure of the complexes and probe the variation of iron redox properties as a function of varying the cyclopentadienyl or halide ligand.
First author: Andjelkovic, L, Nucleus-independent chemical shift profiles along the intrinsicg distortion path for Jahn-Teller active molecules. Study on theg cyclopentadienyl radical and cobaltocene, JOURNAL OF THE SERBIAN CHEMICAL SOCIETY, 80, 877, (2015)
Abstract: The aromatic/anti-aromatic behavior of the cyclopentadienyl anion (Cp-), bis(eta(5)-cyclopentadienypiron(II) (Fe(Cp)(2)), as well as of the Jahn-Teller (JT) active cyclopentadienyl radical (Cp-center dot) and bis(eta(5)-cyclopentadienyl)cobalt(II) (Co(Cp)(2)) were investigated using density functional theory (DFT) calculations of the nuclear independent chemical shifts (NICS). According to the NICS values, pentagon ring in Fe(Cp)(2) is more aromatic than that of the isolated Cp. The NICS parameters were scanned along the Intrinsic Distortion Path (IDP) for Cp-center dot and Co(Cp)(2) showing anti-aromaticity, which decreased with increasing deviation from the high symmetry D-5h to the low symmetry (LS) C-2v. Changes in the NICS values along the IDP revealed that Co(Cp)(2) in the LS nuclear arrangement has aromatic character, in contrast to the case of Cp-center dot.
First author: Kumpulainen, T, Complexes of a naphthalimide photoacid with organic bases, and theirg excited-state dynamics in polar aprotic organic solvents, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 20715, (2015)
Abstract: Complex formation and intermolecular excited-state proton transfer (ESPT) between a dihydroxy-1,8-naphthalimide photoacid and organic bases are investigated in polar aprotic solvents. First, quantum chemical calculations are used to explore the acid-base and spectroscopic properties and to identify energetically favorable complexes. The two hydroxyl groups of the photoacid enable stepwise formation of 1 : 1 and 1 : 2 complexes. Weak bases exhibit only hydrogen-bonding interactions whereas strong bases are able to deprotonate one of the hydroxyl groups resulting in strong negative cooperativity (K-1 >> 4K(2)) in the formation of the 1 : 2 complex. Time-resolved fluorescence studies of the complexes provide strong indications of a three-step dissociation process. The species involved in the model are: a hydrogen-bonded complex, a hydrogen-bonded ion pair, a solvent separated ion pair, and a free ion pair.
First author: Jin, R, Distortion-interaction analysis along the reaction pathway to reveal theg reactivity of the Alder-ene reaction of enes, RSC ADVANCES, 5, 61426, (2015)
Abstract: The reactivity of hetero-substituted propylene in uncatalyzed Alder-ene type reactions was investigated using CBS-QB3, G3B3, M11, and B3LYP methods, and the results are interpreted by distortion-interaction analysis of both the transition states and the complete reaction pathways. The reactivity trend for third-period element substituted ene reactants (ethylidenesilane, ethylidenephosphine, and ethanethial) is higher than that of the corresponding second-period element substituted ene reactants (propylene, ethanimine, and acetaldehyde). Theoretical calculations also indicate that for the same period element substituted ene reactants, the reactivity trend is ethylidenesilane > ethylidenephosphine > ethanethial, and propylene > ethanimine > acetaldehyde. Application of distortion-interaction analysis only of the transition states does not give a satisfactory explanation for these reactivities. Using distortion-interaction analysis along the reaction pathways, we found that the reactivity is mainly controlled by the interaction energy. A lower interaction energy along the reaction pathway leads to an earlier transition state and a lower activation energy, which also can be attributed to orbital interaction, closed-shell repulsion, and static repulsion. In some cases, the distortion energy also influences the reactivity.
First author: Klinger, M, UV photoexcitation of a dissolved metalloid Ge-9 cluster compound andg its extensive ultrafast response, CHEMICAL COMMUNICATIONS, 51, 12278, (2015)
Abstract: Femtosecond pump-probe absorption spectroscopy in tetrahydrofuran solution has been used to investigate the dynamics of a metalloid cluster compound {Ge-9[Si(SiMe3)(3)](3)}(-) 1. Upon UV photoexcitation, the transients in the near-infrared spectral region showed signatures reminiscent of excess electrons in THF (bound or quasi-free) whereas in the visible part excited state dynamics of the cluster complex dominates.
First author: Ghosh, R, The effect of cluster size on the optical band gap energy of Zn-basedg metal-organic frameworks, DALTON TRANSACTIONS, 44, 13464, (2015)
Abstract: We have synthesized three Metal-Organic Frameworks (MOFs) in which Zn metal ions form the secondary building unit, and 4,4′-sulfonyldibenzoic acid (SDB) serves as the ligand: [[Zn(DMF)(SDB)]-(DMF), 1, [Zn-3(DMF)(3)(SDB)(3)](DMF), 2 and [Zn-3(OH)(2)(SDB)(2)] (DMF)(2), 3, where DMF = dimethyl formamide]. Compound 1 contains a paddle-wheel type Zn dimer, compound 2 contains a Zn trimer motif, and 3 contains a one-dimensional Zn-OH-Zn chain. These building units may be considered to be Zn clusters. We have measured and theoretically calculated the band gap energy and by theoretical investigations we found that the cluster size plays an important role in the band gap energy, however additional effects are observed. The larger cluster size corresponds to a larger band gap energy, however the cavity of the trimer based compound (2) traps a solvent molecule that decreases the band gap energy.
First author: Remya, K, Intermolecular carbon-carbon, nitrogen-nitrogen and oxygen-oxygeng non-covalent bonding in dipolar molecules, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 18380, (2015)
Abstract: Clear evidence for the existence of intermolecular carbon-carbon (C center dot center dot center dot C), nitrogen-nitrogen (N center dot center dot center dot N) and oxygen-oxygen (O center dot center dot center dot O) interactions between atoms in similar chemical environments in homogeneous dimers of organic dipolar molecules has been obtained from molecular orbital (MO), natural bond orbital (NBO) and atoms-in-molecule (AIM) electron density analyses at the M06L/6-311++G(d, p) level of density functional theory (DFT). These X center dot center dot center dot X type interactions are mainly the result of local polarization effects, causing segregation of electron-rich and electron-deficient regions in the X atoms, leading to complementary electrostatic interactions. NBO analysis provides evidence of charge transfer between the two X atoms. Even in symmetrical molecules such as acetylene, induced dipoles in the dimer create C center dot center dot center dot C bonding interactions. The strength of this type of interaction increases with increase in the dipole moment of the molecule. Energy decomposition analysis (EDA) shows that the electrostatic component of the interaction energy (E-int) is very high, up to 95.86%. The C center dot center dot center dot C interactions between similar carbon atoms are located for several crystal structures obtained from the literature. In addition, MO, AIM and electrostatic potential analyses support interactions between similar oxygen (O center dot center dot center dot O) and nitrogen (N center dot center dot center dot N) atoms in a variety of molecular dimers. Good prediction of E-int is achieved in terms of the total gain in electron density at non-covalently interacting intermolecular bonds (Sigma rho) and the monomer dipole moment (mu). A rigorously tested QSAR equation has been derived to predict E-int for all dimer systems:
First author: Ramanantoanina, H, Development and applications of the LFDFT: the non-empirical account ofg ligand field and the simulation of the f-d transitions by densityg functional theory, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 18547, (2015)
Abstract: Ligand field density functional theory (LFDFT) is a methodology consisting of non-standard handling of DFT calculations and post-computation analysis, emulating the ligand field parameters in a non-empirical way. Recently, the procedure was extended for two-open-shell systems, with relevance for inter-shell transitions in lanthanides, of utmost importance in understanding the optical and magnetic properties of rare-earth materials. Here, we expand the model to the calculation of intensities of f -> d transitions, enabling the simulation of spectral profiles. We focus on Eu2+-based systems: this lanthanide ion undergoes many dipole-allowed transitions from the initial 4f(7)(S-8(7/2)) state to the final 4f(6)5d(1) ones, considering the free ion and doped materials. The relativistic calculations showed a good agreement with experimental data for a gaseous Eu2+ ion, producing reliable Slater-Condon and spin-orbit coupling parameters. The Eu2+ ion-doped fluorite-type lattices, CaF2:Eu2+ and SrCl2:Eu2+, in sites with octahedral symmetry, are studied in detail. The related Slater-Condon and spin-orbit coupling parameters from the doped materials are compared to those for the free ion, revealing small changes for the 4f shell side and relatively important shifts for those associated with the 5d shell. The ligand field scheme, in Wybourne parameterization, shows a good agreement with the phenomenological interpretation of the experiment. The non-empirical computed parameters are used to calculate the energy and intensity of the 4f(7)-4f(6)5d(1) transitions, rendering a realistic convoluted spectrum.
First author: Viesser, RV, Effects of stereoelectronic interactions on the relativistic spin-orbitg and paramagnetic components of the C-13 NMR shielding tensors ofg dihaloethenes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 19315, (2015)
Abstract: In this study, stereoelectronic interactions were considered to explain the experimental difference in the magnitude of the known heavy-atom effect on the C-13 NMR chemical shifts in cis- and trans-1,2-dihaloethene isomers (halo = F, Cl, Br or I). The experimental values were compared to the calculated values with various DFT functionals using both the nonrelativistic approach (NR) and the relativistic approximations SR-ZORA (SR) and SO-ZORA (SO). NBO and NLMO contributions to the C-13 NMR shielding tensors were determined to assess which stereoelectronic interactions have a more important effect on the shielding tensor in each principal axis system (PAS) coordinate. These analyses associated with the orbital rotation model and the HOMO-LUMO energy gap enable rationalization of trends between cis and trans isomers from fluorine to iodine derivatives. Both paramagnetic and SO shielding terms were responsible for the observed trends. It was possible to conclude that the steric interactions between the two iodine atoms and the hyperconjugative interactions involving the halogen lone pairs (LP(X)) and pi CQC*, sigma CQC* and sigma C-X* antibonding orbitals are responsible for the lower C-13 NMR shielding for the cis isomers of the bromine and the iodine compounds than that of the trans isomers.
First author: Mandal, S, An anion induced multisignaling probe for Hg2+ and its application forg fish kidney and liver tissue imaging studies, DALTON TRANSACTIONS, 44, 13186, (2015)
Abstract: 3′,6′-Bis(diethylamino)-2-(pyridin-2-ylmethyl)spiro[isoindoline-1,9′-xanthen]-3-one (L) was synthesized for the selective fluorescence and colorimetric recognition of Hg2+ at pH 6.0. In addition, L was useful for imaging Hg2+ in fish kidney and liver tissues using a fluorescence microscope. Spirolactam ring opening of L for Hg2+ recognition is strongly influenced by the nature of the mercury salt and found to be NO3–induced. Other mercury salts such as HgCl2, Hg(CH3COO)(2) and Hg(ClO4)(2) failed to induce fluorescence and colorimetric response of L under the same experimental conditions. For instance, the former salt does not exhibit spirolactam ring opening but forms a new ionic compound (H3L)(2)[Hg6Cl18]center dot 2H(2)O (1), whose structure has been elucidated by single crystal X-ray diffraction. This might be explained by (1) the higher covalent nature of Hg2+ and, hence, the lower acidity of the metal center and its inability to induce the ring opening reaction, and (2) the bulky anion, in the case of Hg(ClO4)(2), which is also ionic, faces steric hindrance to accommodate within the N(Et)(2) group upon spirolactam ring opening.
First author: Landman, M, Fischer aminocarbene conformers containing a 2-thienyl or 2-furyl ring:g a crystallographic, NMR, and DFT study, JOURNAL OF COORDINATION CHEMISTRY, 68, 2388, (2015)
Abstract: Fischer aminocarbene complexes [(CO)(5)M=C(NHR)Y] (M=Cr or W; R=H, Cy or C2H4NH2; Y=2-thienyl or 2-furyl) containing an amino group exist as two isomers in solution, the E and Z isomers. The two isomers arise from restricted rotation about the N-C-carbene bond, that exhibits double bond character due to -donation from nitrogen to the carbene carbon. Each isomer exists as two conformers in fast equilibrium with each other. The conformers arise from the rotation of the aryl ring around the C-carbene-C-aryl single bond with a DFT calculated rotation barrier of 0.1-0.5eV. The main isomer, isolated in the solid state, generally exhibits a syn orientation of the aryl ring relative to the amino substituent and a Z configuration of the amino substituent relative to the metal.
First author: Mehmood, U, Density Functional Theory Study on the Electronic Structures ofg Oxadiazole Based Dyes as Photosensitizer for Dye Sensitized Solar Cells, ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, 68, 2388, (2015)
Abstract: The molecular structures and UV-visible absorption spectra of complex photosensitizers comprising oxadiazole isomers as the pi-bridges were analyzed by density functional theory (DFT) and time-dependent DFT. The ground state and excited state oxidation potentials, HOMOs and LUMOs energy levels, and electron injection from the dyes to semiconductor TiO2 have been computed in vacuum here. The results show that all of the dyes may potentially be good photosensitizers in DSSC. To justify the simulation basis, N3 dye was also simulated under the similar conditions. Simulated absorption spectrum, HOMO, LUMO, and band gap values of N3 were compared with the experimental values. We also computed the electronic structure properties and absorption spectra of dye/(TiO2)(8) systems to elucidate the electron injection efficiency at the interface. This work is expected to give proper orientation for experimental synthesis.
First author: Joly, D, Metal-free organic sensitizers with narrow absorption in the visible forg solar cells exceeding 10% efficiency, ENERGY & ENVIRONMENTAL SCIENCE, 8, 2010, (2015)
Abstract: A novel family of six donor-acceptor type organic sensitizers for dye-sensitized solar cells (DSSCs) is reported. The dyes have been designed to have outstanding light absorption properties in the visible range and being able to achieve high photon-to-electrical current conversion for BIPV (building-integrated photovoltaic). Moreover, stability tests under illumination at 1 Sun and 65 degrees C showed a great stability for some of the devices, with less than 6% decrease of power conversion efficiency after 3000 hours. The differences in the performance of the six sensitizers under standard illumination conditions can be correlated with the observed differences in the photo-induced transient photovoltage and in charge extraction measurements. We report the use of one of the dyes for the fabrication of semi-transparent solar modules showing an active area of 1400 cm(2) and a power output of 10.5 W m(-2).
First author: Navamani, K, Forth-back oscillated charge carrier motion in dynamically disorderedg hexathienocoronene molecules: a theoretical study, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 17729, (2015)
Abstract: Electronic structure calculations were performed to investigate the charge transport properties of hexathienocoronene (HTC) based molecules. The effective displacement of the charge carrier along the pi-orbital of nearby molecules is calculated by monitoring the forth and back oscillations of the charge carrier through kinetic Monte Carlo simulation. The charge transport parameters such as charge transfer rate, mobility, hopping conductivity, localized charge density, time average effective mass and degeneracy pressure are calculated and used to study the charge transport mechanism in the studied molecules. The existence of degeneracy levels facilitates the charge transfer and is analyzed through degeneracy pressure. Theoretical results show that the site energy difference in the dynamically disordered system controls the forth-back oscillation of charge carrier and facilitates the unidirectional charge transport mechanism along the sequential localized sites. The ethyl substituted HTC has good hole and electron hopping conductivity of 415 and 894 S cm(-1), respectively, whereas unsubstituted HTC has the small hole mobility of 0.06 cm(2) V-1 s(-1) which is due to large average effective mass of 1.42 x 10(-28) kg.
First author: Henkensmeier, D, Tetrazole substituted polymers for high temperature polymer electrolyteg fuel cells, JOURNAL OF MATERIALS CHEMISTRY A, 3, 14389, (2015)
Abstract: While tetrazole (TZ) has much lower basicity than imidazole and may not be fully protonated in the presence of phosphoric acid (PA), DFT calculations suggest that the basicity of TZ groups can be increased by the introduction of a 2,6-dioxy-phenyl-group in position 5 of TZ. This structure allows hydrogen bonds between TZ protons and ether oxygen atoms, and thereby establishes a resonance stabilised, co-planar structure for tetrazolium ions. Molecular electrostatic potential (MEP) calculations also indicate that tetrazolium ions possess two sites for proton hopping. This makes such materials interesting for use in a high temperature fuel cell (HT PEMFC). Based on these findings, two polymers incorporating the proposed TZ groups were synthesised, formed into membranes, doped with PA and tested for fuel cell relevant properties. At room temperature, TZ-PEEN and commercial meta-PBI showed an equilibrium uptake of 0.5 and 4.7 mol PA per mol heterocycle, respectively, indicating that PBI has higher affinity for PA than TZ-PEEN. The highest achieved PA uptake was ca. 110 wt%, resulting in a proton conductivity of 25 mS cm(-1) at 160 degrees C with a low activation energy of about 35 kJ mol(-1). In a first HT PEMFC test at 160 degrees C, a peak power density of 287 mW cm(-2) was achieved.
First author: Vats, B, Synthesis, structural and theoretical studies of dithiodiglycolamideg compounds of palladium(II), DALTON TRANSACTIONS, 44, 11867, (2015)
Abstract: The reaction of palladium(II) halide with dithiodiglycolamide ligands yielded compounds of the type [PdX2L] (where X = Cl, L = ((CH2SCH2CONPr2)-Pr-i)(2) (1); L = ((CH2SCH2CONBu2)-Bu-i)(2) (2); L = (CH2SCH2CONBu2)(2) (3); L = C7H6((SCH2CONBu2)-Bu-i)(2) (4); X = Br, L = ((CH2SCH2CONBu2)-Bu-i)(2) (5); X = I, L = ((CH2SCH2CONBu2)-Bu-i)(2) (6)), whereas palladium(II) nitrate yielded compounds of the type [PdL2](NO3)(2) (where L = ((CH2SCH2CONPr2)-Pr-i)(2) (7); L = (CH2SCH2CON(i)Bu2)(2) (8)). All compounds were characterized by using IR, H-1 NMR spectral techniques and CHN analyses. The structures of compounds 4, 5 and 7 have been determined by using X-ray diffraction methods. The structures show that the ligands bond through the thioether group to the metal centre in all compounds. They show further that the palladium(II) ion is surrounded by four atoms (two halogens and two thio groups in 4 and 5 and four thio groups in 7) in a square planar arrangement. The dithiodiglycolamide ligand acts as a bidentate chelating ligand and bonds through both the thioether groups to the metal centre, leaving the carbamoyl groups uncoordinated. Theoretical studies reveal that the 1 : 2 compound is energetically more stable and nicely correlates with the IR carbamoyl stretching frequencies as compared to the 1 : 1 compound in which the ligand acts as a tetradentate ligand.
First author: Evans, DA, Photophysical tuning of the aggregation-induced emission of a series ofg para-substituted aryl bis (imino)acenaphthene zinc complexes, DALTON TRANSACTIONS, 44, 11984, (2015)
Abstract: Bis(imino)acenaphthene (BIAN) zinc complexes with para-substituted aryl groups have been synthesized and investigated from the standpoint of their photophysical properties. Each complex was found to be nonemissive in solution. However, complexes 1-6 turned out to be emissive in the solid state, while complexes 7 and 8 remained nonemissive. The emissions for complexes 1-8 displayed color tunability ranging from red-yellow. A detailed crystallographic study of the "as-synthesized" structures revealed a distinct difference in the crystal packing environments of the emissive and nonemissive complexes. Furthermore, a solvatomorphic study provided further emission tunability via changes in the crystal packing environments of each solvatomorph. Lastly, TD-DFT calculations were performed in order to investigate the effect of different para-substituents on the flanking aryl rings of the BIAN ligand.
First author: Skara, G, Revealing the thermodynamic driving force for ligand-based reductions ing quinoids; conceptual rules for designing redox active and non-innocentg ligands, CHEMICAL SCIENCE, 6, 4109, (2015)
Abstract: Metal and ligand-based reductions have been modeled in octahedral ruthenium complexes revealing metal-ligand interactions as the profound driving force for the redox-active behaviour of orthoquinoid-type ligands. Through an extensive investigation of redox-active ligands we revealed the most critical factors that facilitate or suppress redox-activity of ligands in metal complexes, from which basic rules for designing non-innocent/redox-active ligands can be put forward. These rules also allow rational redox-leveling, i.e. the moderation of redox potentials of ligand-centred electron transfer processes, potentially leading to catalysts with low overpotential in multielectron activation processes.
First author: Gorczak, N, Charge transfer versus molecular conductance: molecular orbital symmetryg turns quantum interference rules upside down, CHEMICAL SCIENCE, 6, 4196, (2015)
Abstract: Destructive quantum interference has been shown to strongly reduce charge tunneling rates across molecular bridges. The current consensus is that destructive quantum interference occurs in cross-conjugated molecules, while linearly conjugated molecules exhibit constructive interference. Our experimental results on photoinduced charge transfer in donor-bridge-acceptor systems, however, show that hole transfer is ten times faster through a cross-conjugated biphenyl bridge than through a linearly conjugated biphenyl bridge. Electronic structure calculations reveal that the surprisingly low hole transfer rate across the linearly conjugated biphenyl bridge is caused by the presence of destructive instead of constructive interference. We find that the specific molecular orbital symmetry of the involved donor and acceptor states leads to interference conditions that are different from those valid in single molecule conduction experiments. Furthermore, the results indicate that by utilizing molecular orbital symmetry in a smart way new opportunities of engineering charge transfer emerge.
First author: Lankelma, M, A novel one-dimensional chain built of vanadyl ions andg pyrazine-2,5-dicarboxylate, DALTON TRANSACTIONS, 44, 11380, (2015)
Abstract: We present a new coordination polymer, {[VO(pzdc)(H2O)(2)] H2O}(n), built from vanadyl and pyrazine-2,5-dicarboxylate (pzdc) ions. It consists of a one-dimensional chain of vanadyl ions linked by pzdc ions. The carboxylate groups show monodentate coordination, while the pyrazine ring is present both in non-coordinated and coordinated modes. This novel structure is stabilized by an intricate network of hydrogen bonds. The material is highly robust, and thermally stable up to 400 K. It is also antiferromagnetic, with a maximum magnetic susceptibility at ca. 50 K. The orbital shape and population analysis by means of DFT analysis confirm the pi-acceptor role of the aromatic nitrogen function of the ligand, while the oxygen-based moieties (carboxylates from pzdc, the aqua ligands and oxo from V=O group) behave as normal donors. Charting the density flow related with significant transitions computed by time-dependent DFT, we determined the ligand-to-metal charge transfer processes. The topology of the chain complex implies two different types of connecting bridges. Using Broken Symmetry DFT modelling gives evidence for two different exchange coupling mechanisms between the vanadyl ions along each of these two molecular bridges. One is strongly antiferromagnetic, practically reducing the chain to 'vanadyl dimers'. The other is almost uncoupled, due to the large distance between the vanadyl ions.
First author: Chauhan, V, Geometry controls the stability of FeSi14, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 15718, (2015)
Abstract: First-principles theoretical studies have been carried out to investigate the stability of Sin cages impregnated with a Fe atom. It is shown that FeSi9, FeSi11, and FeSi14 clusters exhibit enhanced local stability as seen through an increase in Si binding energy, Fe embedding energy, the gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), and the Ionization Potential (IP). The conventional picture for the stability of such species combines an assumption of electron precise bonding with the 18-electron rule; however, we find this to be inadequate to explain the enhanced stability in FeSi11 and FeSi14 because the d-band is filled for all FeSin clusters for n >= 9. FeSi14 is shown to be the most stable due to a compact and highly symmetric Si-14 cage with octahedral symmetry that allows better mixing between Fe 3d- and Si 3p-electronic states.
First author: Momeni, MR, Interplay of donor-acceptor interactions in stabilizing boron nitrideg compounds: insights from theory, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 16525, (2015)
Abstract: The stability of a variety of linear and cyclic (BN)(n) (n = 1-3) adducts with N-heterocyclic carbene (ImMe(2); ImMe(2) = [(HCNMe)(2)C:]), N-heterocyclic olefin (ImMe(2)CH(2)) and Wittig (Me3PCH2) donors has been examined using M05-2X/cc-pVTZ computations. The strength and nature of the bonds have been investigated using natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses. Complementary energy decomposition analysis (EDA-NOCV) has been carried out based on BP86/TZ2P computations. In agreement with NBO and AIM analyses, the orbital interaction energy obtained from EDA contributes at least 50% to the total attractive interactions for the carbon-boron bonds indicating their largely covalent nature. The feasibility of isolating monomeric (BN)(n) units using a donor/acceptor protocol was also investigated in a series of adducts of the general form: LB center dot(BN)(n)center dot BH3 and LB center dot(BN)(n)center dot W(CO)(5) (n = 1-3; LB = Lewis bases). Moreover, EDA-NOCV analysis of ImMe(2)center dot BN center dot W(CO)(5) and ImMe(2)center dot B3N3 center dot W(CO)(5) shows that the carbene-boron bonds are stronger in the presence of W(CO)(5) as a Lewis acid mainly because of a dramatic decrease in the amount of Pauli repulsion rather than an increase in the electrostatic/orbital attraction terms.
First author: Pedrosa, S, Imido-pyridine Ti(IV) compounds: synthesis of unusual imido-amidog heterobimetallic derivatives, DALTON TRANSACTIONS, 44, 11119, (2015)
Abstract: The reaction of lithiated picolines and [TiCl3(eta(5)-C5Me5)] leads to several bridging or terminal imido compounds, each of which can be selectively formed by controlling the stoichiometry and temperature. Specifically, the dinuclear imido-bridged [TiCl(eta(5)-C5Me5)(mu-NR)](2) (1a, NR = 2-imido-3-picoline; 1b, NR = 2-imido-5-picoline) species and the unusual Ti-Li imido-amido heterobimetallic complex [{Li(THF)}-{ Ti(eta(5)-C5Me5)(NR)(NHR)(2)}] (2a, NR = 2-imido-3-picoline; 2b, NR = 2-imido-5-picoline) were isolated. Compounds 2 are in effect the first structurally characterized examples of titanium(IV) coordinated to terminal imido-pyridines. DFT-D calculations for 2a denote a multiple bond character between titanium and the imido ligand and a strong polarization of the electron density by the alkali cation in spite of the lack of intermetallic bonding.
First author: Izakmehri, Z, Removal of dioxane pollutants from water by using Al-doped single walledg carbon nanotubes, RSC ADVANCES, 5, 48124, (2015)
Abstract: The detection and fast enrichment of toxic organic pollutants are challenging issues in the field of environmental science. We have studied the adsorption of dioxane on perfect, defected, and Al-doped CNTs by DFT calculations adopting the vdW forces corrections (vdW-DF). The accuracy of the vdW-DF results have been evaluated against the state-of-the-art B3LYP-D3 level of theory and it was shown that there is good agreement between the two respective methods. It was found that the dioxane adsorption ability of Al-CNT is much better (stronger) than perfect and defected CNTs. Calculations of the adsorption behavior of water molecules as a solvent demonstrate the existence of a stronger interaction between dioxane and Al-CNT in comparison with water molecules. Finally, we studied the interaction of dioxane molecules with CNT and Al-CNT in the presence of water molecules in ambient conditions using a DFTB-MD simulation. We showed that dioxane in the presence of water molecules is weakly bound (physisorption) to the outer surface of CNTs while it can be adsorbed on the Al-CNT system stronger than the water molecules as a competitor. Our study provides a molecular level understanding of the interactions between dioxane and CNTs and may be instructive for toxicity agent adsorption and detection from environment.
First author: Zhao, ZY, A sensor for formaldehyde detection: luminescent metal-organic frameworkg [Zn-2(H2L)(2,2 '-bpy)(2)(H2O)](n), RSC ADVANCES, 5, 49752, (2015)
Abstract: Density functional theory and time-dependent density functional theory methods have been used to investigate the hydrogen bonding between the Metal-organic framework [Zn-2(H2L)(2,2′-bpy)(2)(H2O)](n) and formaldehyde in the electronically excited state. The calculated geometric configuration, H-1 NMR chemical shift and IR spectra of the hydrogen-bonded complex demonstrated that the hydrogen bond was strengthened in the excited state S-1. The strengthening of the hydrogen bond in the S1 state would lead to a luminescence decreasing phenomenon of [Zn-2(H2L)(2,2′-bpy)(2)(H2O)](n), and the fluorescent rate constant of [Zn-2(H2L)(2,2′-bpy)(2)(H2O)](n) was decreased when encapsulating formaldehyde into it. Taken together, these results indicated that [Zn-2(H2L)(2,2′-bpy)(2)(H2O)](n) could be used for the detection of formaldehyde.
First author: Schluns, D, Subsystem-DFT potential-energy curves for weakly interacting systems, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 14323, (2015)
Abstract: Kohn-Sham density-functional theory (DFT) within the local-density approximation (LDA) or the generalized-gradient approximation (GGA) is known to fail for the correct description of London dispersion interactions. Often, not even bound potential-energy surfaces are obtained for van der Waals complexes, unless special correction schemes are employed. In contrast to that, there has been some evidence for the fact that subsystem-based density functional theory produces interaction energies for weakly bound systems which are superior to Kohn-Sham DFT results without dispersion corrections. This is usually attributed to an error cancellation between the approximate exchange-correlation and non-additive kinetic-energy functionals employed in subsystem DFT. Here, we investigate the accuracy of subsystem DFT for weakly interacting systems in detail, paying special attention to the shape of the potential-energy surfaces (PESs). Our test sets include the extensive S22x5 and S66x8 data sets. Our results indicate that subsystem DFT PESs strongly vary depending on the functional. LDA results are usually quite good, but behave differently from their KS counterparts. GGA results from the popular Perdew-Wang (PW91) set of functionals produce PESs that are often, but not in general overbinding. Results from Becke-Perdew (BP86) GGAs, by contrast, show the typical problems known from the corresponding KS results. We provide some preliminary results for empirical corrections for both PW91 and BP86 in subsystem DFT.
First author: Kubas, A, Electronic couplings for molecular charge transfer: benchmarking CDFT,g FODFT and FODFTB against high-level ab initio calculations. II, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 14342, (2015)
Abstract: A new database (HAB7-) of electronic coupling matrix elements (H-ab) for electron transfer in seven medium-sized negatively charged pi-conjugated organic dimers is introduced. Reference data are obtained with spin-component scaled approximate coupled cluster method (SCS-CC2) and large basis sets. Assessed DFT-based approaches include constrained density functional theory (CDFT), fragment-orbital DFT (FODFT), self-consistent charge density functional tight-binding (FODFTB) and the recently described analytic overlap method (AOM). This complements the previously reported HAB11 database where only cationic dimers were considered. The CDFT method in combination with a functional based on PBE and including 50% of exact exchange (HFX) was found to provide best estimates, with a mean relative unsigned error (MRUE) of 8.2%. CDFT couplings systematically increase with decreasing fraction of HFX as a consequence of increasing delocalisation of the SOMO orbital. The FODFT method is found to be very robust underestimating electronic couplings by 28%. The FODFTB and AOM methods, although orders of magnitude more efficient in terms of computational effort than the DFT approaches, perform well with reasonably small errors of 54% and 29%, respectively, translating in errors in the nonadiabatic electron transfer rate of a factor of 2.4 and 1.7, respectively. We discuss carefully various sources of errors and the scope and limitations of all assessed methods taking into account the results obtained for both HAB7- and HAB11 databases.
First author: Prlj, A, Excited state dynamics of thiophene and bithiophene: new insights intog theoretically challenging systems, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 14719, (2015)
Abstract: The computational elucidation and proper description of the ultrafast deactivation mechanisms of simple organic electronic units, such as thiophene and its oligomers, is as challenging as it is contentious. A comprehensive excited state dynamics analysis of these systems utilizing reliable electronic structure approaches is currently lacking, with earlier pictures of the photochemistry of these systems being conceived based upon high-level static computations or lower level dynamic trajectories. Here a detailed surface hopping molecular dynamics of thiophene and bithiophene using the algebraic diagrammatic construction to second order (ADC(2)) method is presented. Our findings illustrate that ring puckering plays an important role in thiophene photochemistry and that the photostability increases when going upon dimerization into bithiophene.
First author: Vazquez-Lima, H, Cryptic noninnocence: FeNO corroles in a new light, DALTON TRANSACTIONS, 44, 10146, (2015)
Abstract: Multiple lines of evidence, including electronic absorption spectroscopy, infrared spectroscopy, and broken-symmetry DFT calculations, indicate that the well-known FeNO corroles, long assumed to be {FeNO}(6) complexes, are in fact better described as {FeNO}(7)-(corrole(center dot 2-)).
First author: Akbari, A, A quest for stable 2,5-bis(halobora)cyclopentenylidene and its Si, Ge,g Sn and Pb analogs at theoretical levels, RSC ADVANCES, 5, 43319, (2015)
Abstract: Replacing the two nitrogen atoms of Arduengo's N-heterocyclic carbenes (NHCs) with electron deficient boron atoms forms B-heterocyclic carbenes (BHCs) which may appear destabilizing at first glance. Yet, among the 40 optimized singlet (s) and triplet (t) BHCs and their Si, Ge, Sn and Pb homologues (BHEs), eight species are found that show higher stability than their corresponding NHEs for exhibiting wider singlet-triplet energy gaps (Delta E-st), at B3LYP/TZ2P, as well as CBS-QB3 and G4MP2 ab initio levels. Moreover, triplet BHEs assume a planar geometry with a dihedral angle (D1) of about zero degrees. In contrast, their corresponding singlets show a high tendency for puckering with D1 congruent to 66 degrees. The preference of the latter for puckered nonplanar geometries is evidenced by NBO calculations and visually through their frontier molecular orbitals. The main stabilizing interactions appear to be pi- and sigma-bond hyperconjugation across the ring. The resulting eight species that demonstrate higher stability are: 2,5-bis(iodobora) cyclopentensilylene, 2,5-bis(Z-bora) cyclopenten-germylene and -stannylene, for Z = Br and I; as well as 2,5-bis(Z(2)-bora) cyclopentenplumbylene, for Z(2) = Cl, Br and I.
First author: Dairaku, T, Direct detection of the mercury-nitrogen bond in theg thymine-Hg-II-thymine base-pair with Hg-199 NMR spectroscopy, CHEMICAL COMMUNICATIONS, 51, 8488, (2015)
Abstract: We have observed the 1-bond Hg-199-N-15 J-coupling ((1)J(Hg-199,N-15) = 1050 Hz) within the Hg-II-mediated thymine-thymine base pair (T-Hg-II-T). This strikingly large (1)J(Hg-199,N-15) is the first one for canonical sp(2)-nitrogen atoms, which can be a sensitive structure-probe of N-mercurated compounds and a direct evidence for N-mercuration.
First author: Lohar, S, Ratiometric sensing of lysine through the formation of the pyreneg excimer: experimental and computational studies, CHEMICAL COMMUNICATIONS, 51, 8536, (2015)
Abstract: Several pyrene based fluorescent probes undergo lysine assisted monomer to excimer conversion in a ratiometric manner. Intracellular lysine is detected using fluorescence microscopy.
First author: Atkins, AJ, High-resolution X-ray absorption spectroscopy of iron carbonyl complexes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 13937, (2015)
Abstract: We apply high-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) to study iron carbonyl complexes. Mono-, bi-, and tri-nuclear carbonyl complexes and pure carbonyl complexes as well as carbonyl complexes containing hydrocarbon ligands are considered. The HERFD-XANES spectra reveal multiple pre-edge peaks with individual signatures for each complex, which could not be detected previously with conventional XANES spectroscopy. These peaks are assigned and analysed with the help of TD-DFT calculations. We demonstrate that the pre-edge peaks can be used to distinguish the different types of iron-iron interactions in carbonyl complexes. This opens up new possibilities for applying HERFD-XANES spectroscopy to probe the electronic structure of iron catalysts.
First author: Poggio, S, Properties of transition metal substituted zinc sulfide hexamers andg dodecamers, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 14208, (2015)
Abstract: Density functional theory was used to study the structural and electronic properties of endohedrally- and substitutionally-doped Zn6S6 and Zn12S12 clusters with first-row transition metal atoms. Generally, the lowest energy electronic state of the cluster is that with the maximum multiplicity (Ti and Cr are exceptions). Substitutionally-doped clusters have greater binding energies (per atom) for both cluster sizes, providing an indication that similar doping will be preferred in the bulk material as well. The results are relevant to thin films of doped ZnS in which cluster formation is likely.
First author: Thornley, WA, Rotameric transformations in the photochemistry ofg TpM(CO)(2)(eta(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W,g and R = H or Me, DALTON TRANSACTIONS, 44, 8007, (2015)
Abstract: Low energy photolysis of TpM(CO)(2)(eta(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = 2-H or 2-Me in PVC matrices at 85 K results in exo/gauche isomerism of the allyl ligand. This transformation comes in contrast to the behaviour observed in cyclopentadienyl analogues which undergo exo/endo isomerism. DFT computations reveal an eta(3) –>eta(1)* –>eta(3) mechanism for the allyl rotameric interconversion where the eta(1)*-allyl intermediate is generated upon MLCT excitation.
First author: Mishima, K, Theoretical studies on the absorption spectra of cis-[Ru(4,4 '-COO-2,2g '-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and panchromatic trans-terpyridyl Rug complexes including strong spin-orbit coupling, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 12317, (2015)
Abstract: In this paper, we theoretically and experimentally investigate the photophysical and chemical characteristics and absorption spectra of various ruthenium complexes in solution used as efficient dye-sensitized solar cells. The target molecules are two well-known complexes, cis-[Ru(4,4′-COO-2,2′-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and trans-terpyridyl Ru. The experimental absorption spectra of these molecules, which show strong spin-orbit (SO) coupling, are simulated using first-order perturbation theory based on time-dependent density functional theory and quantum chemistry calculations. It turns out that the theory can simulate the experimental data very well, which indicates that SO coupling is very important and the mixing between singlet and triplet states is strong in these molecules because of the large SO coupling constant of the Ru atom. The exact absorption spectra can only be reproduced by including the perturbation by SO coupling. The physical and chemical differences between cis-[Ru(4,4′-COO-2,2′-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and trans-terpyridyl Ru complexes are elucidated by natural bond orbital and natural transition orbital analyses. From these analyses, we have found that the two kinds of Ru complexes are quite different in terms of photoexcitation response and chemical bonding between the central Ru atom and the surrounding ligands.
First author: Navamani, K, Effect of dynamic disorder on charge carrier dynamics in Ph4DP andg Ph4DTP molecules, RSC ADVANCES, 5, 38722, (2015)
Abstract: Electronic structure calculations were used to study the charge transport and optical properties of 2,2′,6,6′-tetraphenyldipyranylidene (Ph4DP) and its sulfur analogue 2,2′,6,6′-tetraphenyldithiopyranylidene (Ph4DTP) based molecules. The dynamic disorder effect is included while calculating the charge transfer kinetic parameters such as rate coefficient, disorder drift time, hopping conductivity and mobility of charge carriers through the kinetic Monte Carlo simulations. The existence of degeneracy levels promotes the delocalization of charge carrier and charge transfer. Theoretical results show that if the orbital splitting rate is larger than the static charge transfer rate (O-R > k(static)), the charge transfer is kinetically favored. If O-R < k(static), the charge carrier is potentially trapped in the localized site. In the case of O-R similar to k(static), the charge carrier motion is not affected by the dynamic disorder. The calculated hole mobility in Ph4DP and Ph4DTP molecules is 0.04 and 0.03 cm(2) V-1 s(-1) and is in agreement with the experimental results. It has been found that fluorine and chlorine substituted Ph4DP molecules have good ambipolar transporting character. The absorption and emission spectra were calculated using the time dependent density functional theory (TDDFT) method at the CAM-B3LYP/6-31G(d, p) and M062X/6-31G(d,p) levels of theory. The calculated absorption spectra are in agreement with the experimental results.
First author: Ornso, KB, Design of two-photon molecular tandem architectures for solar cells byg ab initio theory, CHEMICAL SCIENCE, 6, 3018, (2015)
Abstract: An extensive database of spectroscopic properties of molecules from ab initio calculations is used to design molecular complexes for use in tandem solar cells that convert two photons into a single electron-hole pair, thereby increasing the output voltage while covering a wider spectral range. Three different architectures are considered: the first two involve a complex consisting of two dye molecules with appropriately matched frontier orbitals, connected by a molecular diode. Optimized combinations of dye molecules are determined by taking advantage of our computational database of the structural and energetic properties of several thousand porphyrin dyes. The third design is a molecular analogy of the intermediate band solar cell, and involves a single dye molecule with strong intersystem crossing to ensure a long lifetime of the intermediate state. Based on the calculated energy levels and molecular orbitals, energy diagrams are presented for the individual steps in the operation of such tandem solar cells. We find that theoretical open circuit voltages of up to 1.8 V can be achieved using these tandem designs. Questions about the practical implementation of prototypical devices, such as the synthesis of the tandem molecules and potential loss mechanisms, are addressed.
First author: Hao, JY, Dynamic motion of an Lu pair inside a C-76(T-d) cage, RSC ADVANCES, 5, 34383, (2015)
Abstract: Relativistic density functional theory (DFT) computations were performed to investigate the dynamic motion of an encapsulated Lu pair inside a C-76(T-d) cage. The results revealed that the lowest-energy configuration of Lu-2@C-76(T-d) adopts C-2 symmetry; four electrons are transferred to the outer carbon cage and the two encapsulated Lu atoms form a metal-metal single bond (with an electronic structure of Lu-2(4+)@C-76(4-)), and the good electron delocalization in the C-76(4)-(T-d) cage partially contributes the thermodynamic preference of Lu-2@C-76(T-d). The rather small barrier (3.2 kcal mol(-1)) for Lu-2 atoms to hop from one stable site to another leads to flexible motion of the Lu pair inside the parent fullerene cage, and the O-h symmetrical motion trajectory of two Lu atoms is consistent with the STM image. The computed C-13 NMR spectrum with this trajectory also agrees well with the experimental results.
First author: Joy, J, Negative hyperconjugation and red-, blue- or zero-shift in X-Z centerg dot center dot center dot Y complexes, FARADAY DISCUSSIONS, 177, 33, (2015)
Abstract: A generalized explanation is provided for the existence of the red-and blue-shifting nature of X-Z bonds (Z = H, halogens, chalcogens, pnicogens, etc.) in X-Z center dot center dot center dot Y complexes based on computational studies on a selected set of weakly bonded complexes and analysis of existing literature data. The additional electrons and orbitals available on Z in comparison to H make for dramatic differences between the H-bond and the rest of the Z-bonds. The nature of the X-group and its influence on the X-Z bond length in the parent X-Z molecule largely controls the change in the X-Z bond length on X-Z center dot center dot center dot Y bond formation; the Y-group usually influences only the magnitude of the effects controlled by X. The major factors which control the X-Z bond length change are: (a) negative hyperconjugative donation of electron density from X-group to X-Z sigma* antibonding molecular orbital (ABMO) in the parent X-Z, (b) induced negative hyperconjugation from the lone pair of electrons on Z to the antibonding orbitals of the X-group, and (c) charge transfer (CT) from the Y-group to the X-Z sigma* orbital. The exchange repulsion from the Y-group that shifts partial electron density at the X-Z sigma* ABMO back to X leads to blue-shifting and the CT from the Y-group to the sigma* ABMO of X-Z leads to red-shifting. The balance between these two opposing forces decides red-, zero- or blue-shifting. A continuum of behaviour of X-Z bond length variation is inevitable in X-Z center dot center dot center dot Y complexes.
First author: Sadr-Arani, L, Fragmentation mechanisms of cytosine, adenine and guanine ionized bases, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 11813, (2015)
Abstract: The different fragmentation channels of cytosine, adenine and guanine have been studied through DFT calculations. The electronic structure of bases, their cations, and the fragments obtained by breaking bonds provides a good understanding of the fragmentation process that can complete the experimental approach. The calculations allow assigning various fragments to the given peaks. The comparison between the energy required for the formation of fragments and the peak intensity in the mass spectrum is used. For cytosine and guanine the elimination of the HNCO molecule is a major route of dissociation, while for adenine multiple loss of HCN or HNC can be followed up to small fragments. For cytosine, this corresponds to the initial bond cleavage of N3-C4/N1-C2, which represents the main dissociation route. For guanine the release of HNCO is obtained through the N1-C2/C5-C6 bond cleavage ( reverse order also possible) leading to the largest peak of the spectrum. The corresponding energies of 3.5 and 3.9 eV are typically in the range available in the experiments. The loss of NH3 or HCN is also possible but requires more energy. For adenine, fragmentation consists of multiple loss of the HCN molecule and the main route corresponding to HC8N9 loss is followed by the release of HC2N1.
First author: Davari, N, Local electric field factors by a combined charge-transfer andg point-dipole interaction model, RSC ADVANCES, 5, 31594, (2015)
Abstract: A force-field model for the local electric field as a linear response to a frequency-dependent external electric field is presented based on a combined charge-transfer and point-dipole interaction (CT-PDI) force-field model for frequencies through the first absorption maximum. The local electric field provides a measure of the mutual interactions of the molecules with each other, as is important in problems ranging from dielectric breakdown to solvent polarization and energy transfer. It also indicates how resonant excitation of these molecules can perturb Raman scattering by a third molecule located nearby through an intensity borrowing mechanism. The CT-PDI model is a combination of a modified electronegativity equalization model including non-metallic behaviour and a point-dipole interaction model described by atomic polarizabilities which also includes the time-dependence of the atomic charges and atomic dipole moments. A parametrization of frequency-dependent polarizabilities through the first absorption maximum calculated by time-dependent density-functional theory has been extended for a set of hydrocarbon and azobenzene molecules to provide atom-type parameters for the CT-PDI model. As initial model systems, results are presented for the benzene and azobenzene dimers for the local electric field response at points between the molecules and at the atoms in the molecules. As expected, the response depends critically on the intermolecular distance between the monomers. The azobenzene dimer shows a larger local field response at the atoms in the phenyl rings compared to the benzene dimer and the response at the nitrogen atoms is larger than at the hydrogen and carbon atoms in the azobenzene dimer, which can be rationalized qualitatively by the charge and dipole contributions to the local field factor either adding up or to a large extent cancelling each other. At the absorption frequency, the largest local field factor of the benzene dimer is around 6 and for the azobenzene dimer it is around 12, respectively, at typical distances, indicating that the response may be significant.
First author: Gao, Y, A strong charge-transfer effect in surface-enhanced Raman scatteringg induced by valence electrons of actinide elements, RSC ADVANCES, 5, 32198, (2015)
Abstract: Surface-enhanced Raman scattering (SERS) is a powerful spectroscopic technique for highly sensitive molecular detection. As the great radial extent of 5f/6d orbitals is enough to support surface plasmons, SERS substrate materials containing actinide elements might bring a novel enhancement mechanism and even significantly enhanced magnitude. Here we study the SERS of a pyridine molecule on the typical actinide embedded structure Ac@Au-7 and on a similar structure of pure gold Au-8, respectively, using the time-dependent density functional theory (TDDFT) method. The calculated results show that the absorption spectrum of pyridine-Ac@Au-7 at 456 nm presents a strong peak belonging to charge-transfer (CT) transition from the metal to the pyridine molecule. Surprisingly, the corresponding CT-SERS enhancement can reach an order of magnitude of 10(5), which could hardly be achieved in the pure gold systems (about 103-104). Furthermore, electronic structure analysis reveals that the initial orbitals of the CT transition contain a non-ignorable contribution from the 6d electrons of the Ac atom. Meanwhile, the contribution of the 6d electrons can be tuned by changing the conformation of the pyridine-Ac@Au-7 complex. The current findings provide a theoretical basis for exploring and synthesizing SERS materials based on actinide elements, which might subsequently facilitate applications of such structures in nanostructural characterization, single-molecule SERS signal detections and biological molecular recognitions etc.
First author: Goicoechea, JM, On the structural landscape in endohedral silicon and germaniumg clusters, M@Si-12 and M@Ge-12, DALTON TRANSACTIONS, 44, 6755, (2015)
Abstract: Amongst the endohedral clusters of the tetrel elements, M@E-n, the 12-vertex species are unique in that three completely different geometries, the icosahedron (I-h, [Ni@Pb-12](2-)), the hexagonal prism (HP, Cr@Si-12) and the bicapped pentagonal prism (BPP, [Ru@Ge-12](3-)) have been identified in stable molecules. We explore here the origins of this structural diversity by comparing stability patterns across isovalent and isoelectronic series, M@Si-12, M@Ge-12 and [M@Ge-12](3-). The BPP structure dominates the structural landscape for high valence electron counts (57-60) while the HP has a rather narrower window of stability around the 54-56 count. Moreover the preference for an HP structure is unique to silicon: in no case is a rigorously D-6h-symmetric structure the global minimum for M@Ge-12. Distortions from the high-symmetry limits, where present, can be traced to degeneracies or near-degeneracies in the frontier orbital domains. In all cases the structure adopted is that which maximizes the delocalization of electron density between the metal and the cluster cage, such that both components attain stable electronic configurations.
First author: Spinney, HA, The titanium tris-anilide cation [Ti(N[Bu-t]Ar)(3)](+) stabilized as itsg perfluoro-tetra-phenylborate salt: structural characterization andg synthesis in connection with redox activity of 4,4 '-bipyridineg dititanium complexes,DALTON TRANSACTIONS, 44, 6784, (2015)
Abstract: This work explores the reduction of 4,4′-bipyridine using two equivalents of the titanium(III) complex Ti(N[Bu-t]Ar)(3) resulting in formation of a black, crystalline complex, (4,4′-bipy){Ti(N[Bu-t]Ar)(3)}(2), for which an X-ray structure determination is reported. The neutral, black, 4,4′-bipyridine-bridged bimetallic was found to be redox active, with mono-and di-anions being accessible electrochemically, and with the mono- and di-cations also being accessible chemically, and isolable, at least when using the weakly coordinating anion [B(C6F5)(4)](-) as the counter-ion. It proved possible to crystallize the salt [(4,4′-bipy){Ti(N[Bu-t]Ar)(3)}(2)]-[B(C6F5)(4)](2) for a single-crystal X-ray structure investigation; in this instance it was revealed that the aromaticity of the 4,4′-bipyridine ligand, that had been disrupted upon reduction, had been regained. A rare cationic d(0) metal tris-amide complex, shown by X-ray crystallography to contain an intriguing pyramidal TiN3 core geometry, namely {Ti(N[Bu-t]Ar)(3)}(+), could also be isolated when using [B(C6F5)(4)] as the essentially non-interacting counter-ion. This highly reactive cation should be considered as a potential intermediate in the plethora of reactions wherein Ti(N[Bu-t]Ar)(3) has been shown to effect the reduction of substrates including halogenated organic molecules, carbonyl compounds, organic nitriles, and metal complexes.
First author: Mishra, S, A convenient and quantitative route to Sn(IV)-M [M = Ti(IV), Nb(V),g Ta(V)] heterobimetallic precursors for dense mixed-metal oxide ceramics, DALTON TRANSACTIONS, 44, 6848, (2015)
Abstract: The strategy of reacting SnCl4 with M(OR)(x) provided a convenient and quantitative approach to new heterobimetallics with a simple addition formula, [SnCl4M(OR)(x)(HOR)(y)] (M = Ti, Nb, Ta; R = Et, Pr-i, x = 4, 5; y = 0-2) or sometimes an oxo complex [SnCl3(O)Ti-2(OPri)(7)(HOPri)(2)]. The alcoholysis reactions of these heterometallics afforded mixed alkoxo complexes [SnCl4(mu-OEt)(2)M((PrO)-O-i)(x)((PrOH)-O-i)(y)] [M = Ti (x = y = 2), Nb, Ta (x = 3, y = 1)] under mild conditions, or a planar rectangular oxo product [SnCl3(mu-OEt)(2)Nb-(OEt)(2)(EtOH)(mu-O)](2) at refluxing/extended stirring time. DFT calculations shed light on the stability and reactivity of these complexes. The use of these thoroughly characterized heterometallics as sol-gel precursors suppresses the formation of the undesired SnO2 grains, which are difficult to be sintered to a high density. The combined approach of using bottom-up synthesis of mixed Ti0.5Sn0.5O2 nanoparticles and Spark Plasma Sintering allowed the successful densification of chloride-free mixed-metal oxide ceramics. The influence of thermal treatment before sintering on the density and spinodal decomposition of the TiO2-SnO2 pellets is reported.
First author: Widdifield, CM, Solid-state Re-185/187 NMR and GIPAW DFT study of perrhenates andg Re-2(CO)(10): chemical shift anisotropy, NMR crystallography, and ag metal-metal bond, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 10118, (2015)
Abstract: Advances in solid-state nuclear magnetic resonance (SSNMR) methods, such as dynamic nuclear polarization (DNP), intricate pulse sequences, and increased applied magnetic fields, allow for the study of systems which even very recently would be impractical. However, SSNMR methods using certain quadrupolar probe nuclei (i.e., I > 1/2), such as Re-185/187 remain far from fully developed due to the exceedingly strong interaction between the quadrupole moment of these nuclei and local electric field gradients (EFGs). We present a detailed high-field (B-0 = 21.1 T) experimental SSNMR study on several perrhenates (KReO4, AgReO4, Ca(ReO4)(2)center dot 2H(2)O), as well as ReO3 and Re-2(CO)(10). We propose solid ReO3 as a new rhenium SSNMR chemical shift standard due to its reproducible and sharp Re-185/187 NMR resonances. We show that for KReO4, previously poorly understood high-order quadrupole-induced effects (HOQIE) on the satellite transitions can be used to measure the EFG tensor asymmetry (i.e., ZQ) to nearly an order-of-magnitude greater precision than competing SSNMR and nuclear quadrupole resonance (NQR) approaches. Samples of AgReO4 and Ca(ReO4)(2)center dot 2H(2)O enable us to comment on the effects of counter-ions and hydration upon Re(VII) chemical shifts. Calcium-43 and Re-185/187 NMR tensor parameters allow us to conclude that two proposed crystal structures for Ca(ReO4)(2)center dot 2H(2)O, which would be considered as distinct, are in fact the same structure. Study of Re-2(CO)(10) provides insights into the effects of Re-Re bonding on the rhenium NMR tensor parameters and rhenium oxidation state on the Re chemical shift value. As overtone NQR experiments allowed us to precisely measure the Re-185/187 EFG tensor of Re-2(CO)(10), we were able to measure rhenium chemical shift anisotropy (CSA) for the first time in a powdered sample. Experimental observations are supported by gauge-including projector augmented-wave (GIPAW) density functional theory (DFT) calculations, with NMR tensor calculations also provided for NH4ReO4, NaReO4 and RbReO4. These calculations are able to reproduce many of the experimental trends in rhenium diso values and EFG tensor magnitudes. Using KReO4 as a prototypical perrhenate-containing system, we establish a correlation between the tetrahedral shear strain parameter (vertical bar psi vertical bar) and the nuclear electric quadrupolar coupling constant (C-Q), which enables the refinement of the structure of ND4ReO4. Shortcomings in traditional DFT approaches, even when including relativistic effects via the zeroth-order regular approximation (ZORA), for calculating rhenium NMR tensor parameters are identified for Re-2(CO)(10).
First author: Li, SB, Theoretical design and characterization of pyridalthiadiazole-basedg chromophores with fast charge transfer at donor/acceptor interfaceg toward small molecule organic photovoltaics, RSC ADVANCES, 5, 29401, (2015)
Abstract: A class of D-1-A-D-2-A-D-1-type small molecule (SM) donors (2-5) was engineered via modifying or replacing the core donor moiety in three building blocks based on the reported DTS(PTTh2)(2) (1) to screen suitable donor materials for organic photovoltaics (OPV). Density functional theory calculation was performed to investigate the electronic structures, open circuit voltage (V-oc) and key parameters closely relevant to the short-circuit current density (J(sc)), including (i) absorption spectrum, (ii) electron-hole coherence, (iii) energy driving force, (iv) charge transfer dynamics, and (v) carrier transport efficiency. The results manifest that the designed 2-5 show good performance with large V-oc, stable charge transfer and effective charge transport. Surprisingly, the ratios k(inter-CT)/k(inter-CR) of 2/PCBM, 3/PCBM, and 5/PCBM heterojunctions present over 10(4) times higher than that of 1/PCBM. Our conclusions indicate that designed PT-based SMs can better the performance of OPVs, which will provide theoretical guideline for the design and synthesis of new organic SM donors.
First author: Jastrzebski, R, Sustainable production of dimethyl adipate by non-heme iron(III)g catalysed oxidative cleavage of catechol, CATALYSIS SCIENCE & TECHNOLOGY, 5, 2103, (2015)
Abstract: Adipic acid and its esters are important bulk chemicals whose principal use is in the production of the nylon-6,6 polymer. There is considerable interest in finding novel green routes from sustainable feedstocks towards these important intermediates. Herein, we describe the catalytic oxidative cleavage of catechol to muconic acids using a catalyst prepared in situ from iron(III) nitrate, tris(2-pyridylmethyl) amine and ammonium acetate. An investigation of catalyst loading, temperature and oxygen pressure, allowed a turnover frequency of 120 h(-1) to be obtained. The subsequent hydrogenation and transesterification of the obtained muconic acid products were shown to proceed well over commercially available supported catalysts. After vacuum distillation, dimethyl adipate could be isolated in 62% yield from catechol, thus demonstrating a green and sustainable route to this important bulk chemical.
First author: Kather, R, Lewis-acid induced disaggregation of dimeric arylantimony oxides, CHEMICAL COMMUNICATIONS, 51, 5932, (2015)
Abstract: The previously known dimeric arylantimony oxides (Ph3SbO)(2) and [2,6-(Me2NCH2)(2)C6H3SbO](2) were disaggregated by the Lewis acid B(C6F5)(3) giving rise to the formation of the Lewis pair complexes Ph3SbOB(C6F5)(3) and 2,6-(Me2NCH2)(2)C6H3SbOB(C6F5)(3) having short bipolar single Sb-O bonds.
First author: Xiong, XG, On the gold-ligand covalency in linear [AuX2](-) complexes, DALTON TRANSACTIONS, 44, 5535, (2015)
Abstract: Gold compounds, clusters, and nanoparticles are widely used as catalysts and therapeutic medicines; the interactions between gold and its ligands in these systems play important roles in their chemical properties and functionalities. In order to elucidate the nature of the chemical interactions between Au(I) and its ligands, herein we use several theoretical methods to study the chemical bonding in a variety of linear [AuX2](-) complexes, where X = halogen atoms (F, Cl, Br, I, At and Uus), H, OH, SH, OCH3, SCH3, CN and SCN. It is shown that the most important bonding orbitals in these systems have significant contributions from the Au sd hybridized atomic orbitals. The ubiquitous linear or quasi-linear structures of [AuX2](-) are attributed to the well-balanced optimal overlap in both s and p bonding orbitals and minimal repulsion between the two negatively charged ligands. The stability of these complexes is related to the covalency of the Au-X bond and a periodic trend is found in the evolution of covalency along the halogen group ligands. The special stability of [Au(CN)(2)](-) is a result of strong covalent and ionic interactions. For the superheavy element Uus, the covalency of Au-Uus is enhanced through the spin-orbit interactions.
First author: Sterenberg, BT, Binuclear platinum-iridium complexes: synthesis, reactivity andg luminescence, DALTON TRANSACTIONS, 44, 5555, (2015)
Abstract: The chemistry of the heterobinuclear platinum-iridium complex [PtIr(CO)(3)(mu-dppm)(2)][PF6], 1, dppm = Ph2PCH2PPh2, is described. The reaction of a hydride with 1 gave [HPtIr(CO)(2)(mu-dppm)(2)], by displacement of the carbonyl ligand from platinum, while reaction of 1 with dihydrogen, hydrogen chloride or Ph2MeSiH gave the fluxional complex [PtIrH4(CO)(mu-dppm)(2)][PF6], [PtIrH2Cl2(CO)(mu-dppm)(2)][PF6], or [PtIrH(SiMePh2)(CO)(2)(mu-dppm)(2)][PF6], respectively, by oxidative addition at iridium. Complex 1 reacted, often regioselectively, with several alkynes to give the mu-eta(1),eta(1) bridging alkyne complexes [PtIr(mu-RCCR')(CO)(2)(mu-dppm)(2)][PF6], R = H, R' = Ph, 4-C6H4Me, CO2Me; R = Ph, R' = CO2Me; R = R' = CO2Me. The complex [PtIr(mu-HCC-4-C6H4Me)(CO)(2)(mu-dppm)(2)][PF6] reacted reversibly with CO to give [PtIr(mu-HCC-4-C6H4Me)(CO)(3)(mu-dppm)(2)][PF6] and [PtIr(CO)(3)(mu-dppm)(2)][PF6], 1. With HCl, [PtIr(mu-HCC-4C(6)H(4)Me)(CO)(2)(mu-dppm)(2)][PF6] reacted to give [PtIrHCl(mu-HCC-4-C6H4Me)(CO)(2)(mu-dppm)(2)][PF6], by oxidative addition at iridium, and then the alkenylplatinum derivative [PtIrCl{HC=CH(4-C6H4Me)}(CO)(2)(mu-dppm)(2)][PF6]. [PtIr(mu-HCC-4-C6H4Me)(CO)(2)(mu-dppm)(2)][PF6] reacted slowly with dihydrogen to give 4-MeC6H4CH=CH2 and [PtIrH4(CO)(mu-dppm)(2)][PF6]. The complex [PtIr(mu-HCCPh)(CO)(2)(mu-dppm)(2)][PF6] is intensely luminescent in solution at room temperature, with features characteristic of a d(8)-d(8) face-to-face complex.
First author: Behzadi, S, Determination of nanoparticles using UV-Vis spectra, NANOSCALE, 7, 5134, (2015)
Abstract: Nanoparticles (NPs) are increasingly being used in different branches of science and in industrial applications; however, their rapid detection and characterization at low concentration levels have remained a challenge; more specifically, there is no single technique that can characterize the physicochemical properties of NPs (e.g. composition and size). In this work we have developed a colorimetric sensor array for defining the physicochemical properties of NPs in aqueous solution with ultra-low concentrations (e.g. 10(-7)g ml(-1) for gold NPs). Various NPs were readily identified using a standard chemometric approach (i.e. hierarchical clustering analysis), with no misclassifications over 400 trials.
First author: Soto, JR, Reexamination of the origin of the pseudo Jahn-Teller puckeringg instability in silicene, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 7624, (2015)
Abstract: Silicene, the graphene-like crystal formed by the Si hexagonal lattice, presents a periodic buckled structure whose origin is due to the pseudo Jahn-Teller instability on each of its planar six membered rings. This has been attributed to the coupling of the planar D-6h ground state with the first b(2g) excited state through a b(2g) vibrational mode. Here we show, by explicitly calculating the vibronic coupling constants through a complete study of the PJT effect, that the vibronic coupling of the ground state with only one excited state to explain the planar instability is inconsistent with the linear multilevel PJT effect theory. It is also shown that in order to have consistency, the PJT model should include the next excited state, which is symmetry compatible coupled to the puckering mode. This is done by the analysis, based on DFT and TDDFT calculations, of the vibronic instability of the ground state of hexasilabenzene, the basic silicon hydrogenated hexagonal ring unit defining silicene.
First author: Neidhart, SM, Theoretical examination of solvent and R group dependence in goldg thiolate nanoparticle synthesis, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 7676, (2015)
Abstract: The growth of gold thiolate nanoparticles can be affected by the solvent and the R group on the ligand. In this work, the difference between methanol and benzene solvents as well as the effect of alkyl (methyl) and aromatic (phenyl) thiols on the reaction energies and barrier heights is investigated theoretically. Density functional theory (DFT) calculations using the BP86 functional and a triple zeta polarized basis set show that the overall reaction favors methylthiol over phenylthiol with reaction energies of -0.54 and -0.39 eV in methanol, respectively. At the same level of theory, the methanol solvent is favored over the benzene solvent for reactions forming ions; in benzene, the overall reaction energies for methylthiol and phenylthiol reacting with AuCl4- to form Au(HSR)(2)(+) are 0.37 eV and 0.44 eV, respectively. Methylthiol in methanol also has the lowest barrier heights at about 0.3 eV, whereas phenylthiol has barrier heights around 0.4 eV. Barrier heights in benzene are significantly larger than those in methanol.
First author: Moura, RT, Features of chemical bonds based on the overlap polarizabilities:g diatomic and solid-state systems with the frozen-density embeddingg approach, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 7731, (2015)
Abstract: The chemical bond overlap properties were obtained for alkali halides NaY (Y = F, Cl, Br), alkaline-earth chalcogenides MX (M = Ca, Mg and X = O, S, Se) and alkali and alkali-earth metals (Li, Na, and Mg) in diatomic and solid-state systems using an embedding approach based on the frozen density functional theory to simulate the crystalline effects. The computational protocol established provides errors for bond distances smaller than 1%. The results indicate that larger chemical bond covalency leads to larger absorption or scattering by the overlap region. The ionic specific valence and overlap polarizability are closely related to the valence orbital compactness measured by the sum of Mulliken electronegativities. The embedding approach used in this work makes it possible to quantify the effects of the crystalline environment on the chemical bond overlap properties. In the solid-state, the bond overlap charges are less polarizable, in cases of well-known ionic systems (provided by electronegativity differences), leading to smaller chemical bond covalency in solids than in diatomics. The spectroscopic properties of the polarizability of the electron density in the overlap region of a chemical bond could be measured in the 1-20 eV spectral region and could be used to characterize some bands in several spectra whose assignments are ambiguous or not available.
First author: Pascual-Borras, M, Accurate calculation of P-31 NMR chemical shifts in polyoxometalates, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 8723, (2015)
Abstract: We search for the best density functional theory strategy for the determination of P-31 nuclear magnetic resonance (NMR) chemical shifts, delta(P-31), in polyoxometalates. Among the variables governing the quality of the quantum modelling, we tackle herein the influence of the functional and the basis set. The spin-orbit and solvent effects were routinely included. To do so we analysed the family of structures alpha-[P2W18-xMxO62](n-) with M = Mo-VI, V-V or Nb-V; [P2W17O62(M'R)](n-) with M' = Sn-IV, Ge-IV and Ru-II and [PW12-xMxO40](n-) with M = Pd-IV, Nb-V and Ti-IV. The main results suggest that, to date, the best procedure for the accurate calculation of delta(P-31) in polyoxometalates is the combination of TZP/PBE//TZ2P/OPBE (for NMR//optimization step). The hybrid functionals (PBE0, B3LYP) tested herein were applied to the NMR step, besides being more CPU-consuming, do not outperform pure GGA functionals. Although previous studies on W-183 NMR suggested that the use of very large basis sets like QZ4P were needed for geometry optimization, the present results indicate that TZ2P suffices if the functional is optimal. Moreover, scaling corrections were applied to the results providing low mean absolute errors below 1 ppm for delta(P-31), which is a step forward in order to confirm or predict chemical shifts in polyoxometalates. Finally, via a simplified molecular model, we establish how the small variations in delta(P-31) arise from energy changes in the occupied and virtual orbitals of the PO4 group.
First author: Ramanantoanina, H, Tailoring the optical properties of lanthanide phosphors: prediction andg characterization of the luminescence of Pr3+-doped LiYF4, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 9116, (2015)
Abstract: We present a theoretical work detailing the electronic structure and the optical properties of (PrF8)(5)- embedded in LiYF4, complementing the insight with data that are not available by experimental line. The local distortions due to the embedding of the lanthanide ion in the sites occupied in the periodic lattice by smaller yttrium centres, not detectable in regular X-ray analyses, are reproduced with the help of geometry optimization. Then, based on the local coordination environment, the relation structure-optical properties is constructed by Density Functional Theory computations in conjunction with the ligand field theory analyses (LFDFT) determining the [Xe] 4f(2) -> [Xe]4f(1)5d(1) transitions. In previous instances we analysed rather symmetric systems, here facing the complexity of low symmetry cases, treated in the Wybourne ligand field parameterization and in the Angular Overlap Model (AOM) frame. A very important improvement at the AOM level is the consideration of the f-d mixing that brings coupling term of odd-even nature, essential for the realistic description of the asymmetric coordination centres. Furthermore, we introduce now a principle for modelling the emission intensity. The results are in agreement with available experimental findings. The relevance of the modelling has a practical face in the rational design of optimal luminescent materials needed in domestic lightening and also an academic side, revisiting with modern computational tools areas incompletely explored by the standard ligand field theories.
First author: Kolesnikov, VI, Compatibility of chemical elements on grain boundaries in steel and itsg influence on wear resistance of steel, JOURNAL OF FRICTION AND WEAR, 36, 1, (2015)
Abstract: A quantum-chemical analysis of the interaction of atoms of alloying and impurity elements with grain surfaces in steel has been performed. The cluster model and the two-periodic slab model have been used. The compatibility of various elements with iron on grain boundaries in steel has been estimated. The results are in agreement with the known experimental data and correspond to Mendeleev's law. The obtained dependences can be used for predicting strength characteristics of polycrystalline materials with various alloying additives.
First author: Kaczmarzyk, T, Mossbauer study of a tetrakis (pentafluorophenyl) porphyrin iron (III)g chloride in comparison with the fluorine unsubstituted analogue, NUKLEONIKA, 60, 57, (2015)
Abstract: Mossbauer investigations, in association with density functional theory (DFT) calculations, have been conducted for the molecular and electronic structures of iron (III) [tetrakis (pentafluorophenyl)] porphyrin chloride [(F20TPP)Fe:Cl], as a Fe(III)-tetraphenylporphyrin complex containing chloride axial ligand and substituted hydrogen atoms by fluorine ones in the four phenyl rings, in comparison with its fluorine unsubstituted analogue [(TPP)Fe:Cl]. It was found that the parameters of Mossbauer spectra of both complexes are close to one another, and correspond to the high-spin state of Fe(III) ions, but they show the different temperature dependence and the quadrupole doublets in Mossbauer spectra show different asymmetry at low temperatures. Results of DFT calculations are analyzed in the light of catalytic activity of the halogenated complex.
First author: Novak, M, Asymmetric bifurcated halogen bonds, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 6440, (2015)
Abstract: Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as 'sigma-hole – lone pair' or 'sigma-hole – pi' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction.
First author: Morales-Verdejo, CA, Photophysics of tungsten-benzylidyne complexes derived from s-indacene:g synthesis, characterization and DFT studies, RSC ADVANCES, 5, 25594, (2015)
Abstract: The photophysics of the mono-and homobimetallic complexes of tungsten-benzylidyne derived from s-indacene have been examined by using absorption and emission. Theoretical calculations of these compounds were carried out to gain further understanding of these novel molecular systems. Consistent with this prediction, each of the complexes displays a weak, mid-visible absorption band which is attributed to the d -> pi* transition. The tungsten complexes also exhibit luminescence with a lifetime in the 5-6 ns regime.
First author: Nijesh, K, 2-Adamantylidene and its heavier analogues: hyperconjugation versus loneg pair stability and electrophilicity versus nucleophilicity, DALTON TRANSACTIONS, 44, 4693, (2015)
Abstract: The structure, bonding and reactivity of 2-adamantylidene and its heavier group-14 analogues, 2X (X10H14, X = C-Sn), have been studied at the M06/def2-TZVPP//BP86/def2-TZVPP level of theory. 2-Adamantylidene and its heavier analogues, 2X, have a singlet ground state, where the carbene and silylene bridges in 2C and 2Si are bent similarly to the foiled-type carbenes. The bending of the carbene and silylene bridges in 2C and 2Si as well as their stability are mainly attributed to the Cieplak-type hyperconjugative interaction between a pair of vicinal sigma-bonds with the empty p-orbital on the carbon and silicon atoms. However, the inertness of the lone pair of the silicon atom also contributes to the stability of 2Si. The extent of hyperconjugative interactions is significantly less in 2Ge and 2Sn and the inertness of the lone pair is the major factor for their stability. The high proton affinity (PA) and hydride affinity (HA) of 2-adamantylidene and its heavier analogues suggest their ambiphilic nature. The high PA and HA of 2X can be attributed to the stabilization of the protonated adduct, 4X, and the hydride adduct, 5X, by the Cieplak-type and Felkin-Anh-type hyperconjugations, respectively. However, the nucleophilicity of 2X decreases and electrophilicity increases when X changes from C to Sn.
First author: Ferrari, AC, Science and technology roadmap for graphene, related two-dimensionalg crystals, and hybrid systems, NANOSCALE, 7, 4598, (2015)
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.
First author: Baranac-Stojanovic, M, Energy decomposition analysis of gauche preference in 2-haloethanol,g 2-haloethylamine (halogen = F, Cl), their protonated forms and antig preference in 1-chloro-2-fluoroethane, RSC ADVANCES, 5, 22980, (2015)
Abstract: 2-Haloethanol and 2-haloethylamine (halogen = F, Cl) prefer gauche conformation. This preference is significantly increased upon protonation. Commonly used explanations are based on intramolecular hydrogen bonding and hyperconjugation. 1,2-Difluoroethane prefers gauche conformation, too, while gaseous 1-chloro-2-fluoroethane is more stable as the anti conformer. The origin of these conformational preferences has been investigated by a quantitative partitioning of the gauche/anti energy difference into contributions from electrostatic, orbital, dispersion and Pauli interactions, and structural changes accompanying the rotation. The results show that, with two exceptions, the most important contributor to the gauche preference is electrostatic attraction, which is larger in gauche forms relative to the anti ones. Next come orbital interactions, while dispersion forces provide the smallest stabilizing energy. These energy components override destabilizing Pauli interactions and energetically costly structural changes. All gauche preferences also benefit from stereoelectronic effects, except in protonated 2-chloroethanol which, instead, shows a significant Cl lone pair -> O-H antibond mixing, associated with hydrogen bonding. The increase in the Pauli repulsion upon anti to gauche isomerization is more pronounced for fluorine than for chlorine derivatives. Thus, the smaller gauche effect in chloro-compounds and the anti preference in 1-chloro-2-fluoroethane have their origin in the decrease in electrostatic and orbital stabilizing interactions, a drop in the former being more pronounced.
First author: Kuhn, A, Observed hydrolysis of fluorine substitutedg bis(beta-diketonato)-dichlorotitanium(IV) complexes, DALTON TRANSACTIONS, 44, 5106, (2015)
Abstract: Novel fluorine substituted mononuclear Ti(beta-diketonato)(2)Cl-2 complexes have been synthesised and shown to be involved in a partial hydrolysis reaction in solution, in which the hydrolyzed dinuclear {Ti(beta-diketonato)(2)Cl}(2)(mu-O) is in equilibrium with the monomer. This is in contrast to the solution behaviour of the non CF3-containing Ti(CH3COCHCOCH3)(2)Cl-2, Ti(PhCOCHCOCH3)(2)Cl-2 and Ti(PhCOCHCOPh)(2)Cl-2 complexes, under the same conditions. Variable temperature (H-1 and F-19) NMR spectra and X-ray structure analyses reveal that the partially hydrolyzed dinuclear complex exists both in solution and in solid state, bridging through a single mu-oxo bridge and having one labile chloro-ligand per titanium center. Inclusion of electron-withdrawing CF3 groups into the already electron-deficient Ti complexes, led to the formation of {Ti(CF3COCHCOCF3)(2)Cl}(2)(mu-O) (dinuclear) and [Ti(CF3COCHCOCF3)(2)(mu-O)](4) (tetranuclear) complexes in CDCl3 containing trace amounts of water. DFT calculated free energies of hydrolysis support the existence of Ti(CH3COCHCOCH3)(2)Cl-2 as a monomer and Ti(CF3COCHCOCF(3))(2)Cl-2 as a equilibrium mixture of the monomer and partially hydrolyzed dinuclear {Ti(beta-diketonato)(2)Cl}(2)(mu-O) in CDCl3 solution.
First author: Moniodis, JJ, Competitive formation of DNA linkage isomers by a trinuclear platinumg complex and the influence of pre-association, DALTON TRANSACTIONS, 44, 3583, (2015)
Abstract: 2D [ 1H, 15N] HSQC NMR spectroscopy has been used to monitor the reaction of fully 15N- labelled [{transPtCl( NH3) 2} 2( – trans- Pt( NH3) 2{NH2( CH2) 6NH2} 2)] 4+ ( BBR3464 ( 15N- 1)) with the 14- mer duplex ( 5′-{d( ATACATG( 7) G( 8) TACATA)}- 3′ 5′-{d( TATG( 18) TACCATG( 25) TAT)}- 3′ or I) at pH 5.4 and 298 K, to examine the possible formation of 1,4 and 1,5- GG adducts in both 5′- 5′ and 3′- 3′ directions. In a previous study, the binding of the dinuclear 1,1/ t, t to I showed specific formation of the 5′- 5′ 1,4 G( 8) G( 18) crosslink, whereas in this case a mixture of adducts were formed. Initial 1H NMR spectra suggested the presence of two pre- associated states aligned in both directions along the DNA. The pre- association was studied in the absence of covalent binding, by use of the " non- covalent" analog [{transPt( NH3) 3} 2( – trans- Pt( NH3) 2{NH2( CH2) 6NH2} 2)] 6+ ( AH44, 0). Chemical shift changes of DNA protons combined with NOE connectivities between CH2 and NH3 protons of 0 and the adenine H2 protons on I show that two different molecules of 0 are bound in the minor groove. Molecular dynamic simulations were performed to study the interaction of 0 at the two pre- association sites using charges derived from density functional theory ( DFT) calculations. Structures where the central platinum is located in the minor groove and the aliphatic linkers extend into the major groove, in opposite directions, often represent the lowest energy structures of the snapshots selected. In the reaction of 15N- 1 and I, following the preassociation step, aquation occurs to give the mono aqua monochloro species 2, with a rate constant of 3.43 0.03 x 10- 5 s- 1. There was evidence for two monofunctional adducts ( 3, 4) bound to the 3′ ( G8) and 5′ ( G7) residues and the asymmetry of the 1H, 15N peak for 3 suggested two conformers of the 3′ adduct, aligned in different directions along the DNA. The rate constant for combined monofunctional adduct formation ( 0.6 0.1 M- 1) is ca. 2- fold lower for 1 compared to 1,1/ t, t, whereas the rate constant for conversion of the combined monofunctional species to combined bifunctional adducts ( 5) ( 8.0 0.2 x 10- 5 s- 1) is two- fold higher.
First author: Saleh, N, Effect of Molecular-Level Insulation on the Performance of ag Dye-Sensitized Solar Cell: Fluorescence Studies in Solid State, JOURNAL OF FLUORESCENCE, 25, 59, (2015)
Abstract: The performance of a dye-sensitized solar cell (DSSC) that is based on the host-guest encapsulation of 5-[4-diphenylamino)phenyl]thiophene-2-cyanoacrylic acid (L1) inside beta-cyclodextrin hosts has been tested. The formation of the complex in the solid state and when adsorbed on TiO2 was characterized using steady and picosecond time-resolved emission techniques, as well as time dependent DFT calculations. The molecular-level insulation has led to a small enhancement in the energy-conversion performance of the fabricated DSSC with the best results being an increase in the open circuit voltage (Voc) from 0.7 to 0.8 V. The importance of the present investigation lies in the unique spectroscopic characterizations of the examined materials in the solid state.
First author: Mallesham, G, Phosphine oxide functionalized pyrenes as efficient blue light emittingg multifunctional materials for organic light emitting diodes, JOURNAL OF MATERIALS CHEMISTRY C, 3, 1208, (2015)
Abstract: In a search for blue light emitting multifunctional materials, the electron transport enhancing diphenyl phosphine-oxide (Ph2P=O) group has been appended to blue light emitting pyrene derivatives. This design, we observe, leads to highly efficient electron transporting blue-emitters for non-doped organic light emitting devices (OLEDs) with good film formation characteristics. The superior performance is attributed to enhanced charge transport and formation of pyrene excimers assisted by thermally activated delayed fluorescence (TADF) in the device. We report the synthesis and characterization using experimental and computational methods of six such pyrene derivatives. Although three of these derivatives show quenching of luminescence in solvents at higher concentrations, in the thin film invariably all six of them exhibit typical pyrene excimer emission. X-ray crystal analysis reveals pi-pi stacking and the C-H center dot center dot center dot O interactions in the solid due to the P=O group. The measured electron mobilities for all the compounds are higher in comparison to the standard electron transport material, Alq(3). Non-doped OLEDs with the pyrene derivatives as emitters (multi-layer configuration) as well as electron transport cum emitters (bilayer configuration) exhibit excellent efficiencies. The derivatives as emitters display a performance with current efficiencies (eta(c)) in the range 21.1-30.1 cd A(-1), power efficiencies (eta(p)) 11.0-15.76 lm W-1, external quantum efficiencies (EQE) 7.2-9.1% and brightness 28 500-42 750 cd m(-2). In addition, the derivatives as electron transporting emitters demonstrate very good external quantum efficiencies in the range of 3.0-4.0%. These results demonstrate a successful strategy to obtain blue light emitting multifunctional materials for OLED applications.
First author: Hancock, AN, The effect of leaving radical on the formation of tetrahydroselenopheneg by S(H)i ring closure: an experimental and computational study, ORGANIC & BIOMOLECULAR CHEMISTRY, 13, 2310, (2015)
Abstract: Competition kinetic studies augmented with laser-flash photolysis and high-level computational techniques [G3(MP2)-RAD], with [COSMO-RS, SMD] and without solvent correction, provide kinetic parameters for the ring closures of a series of 4-(alkylseleno) butyl radicals 1. At 22 degrees C rate constants (k(c)) that lie between 10(4)-10(7) s(-1) were determined experimentally and correlate with expectations based on leaving group ability. Activation energies (E-act) were determined to lie between 10.6 (R = Ph2CH) and 28.0 (R = n-Bu) kJ mol(-1), while log(A/s(-1)) values were generally between 9 and 10 in benzene. Computationally determined rate constants were in good-to-excellent agreement with those determined experimentally, with the COSMO-RS solvation model providing values that more closely resemble those from experiment than SMD.
First author: Azpiroz, JM, The effect of TiO2 surface on the electron injection efficiency in PbSg quantum dot solar cells: a first-principles study, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 6076, (2015)
Abstract: We present a density functional theory (DFT) study aimed at understanding the injection and recombination processes that occur at the interface between PbS QDs and TiO2 oxide nanoparticles with different morphologies. The calculated injection rates fall in the picosecond timescale in good agreement with the experiments. In addition, our simulations show that the (101) facet of TiO2 more favourably accommodates the QD, resulting in stronger electronic couplings and faster electron injections than the (001) surfaces. Despite this, the (101) slab is also more prone to faster electron recombination with the valence band of the QD, which can lead to overall lower injection efficiencies than the (001) surface.
First author: Vummaleti, SVC, What can NMR spectroscopy of selenoureas and phosphinidenes teach usg about the pi-accepting abilities of N-heterocyclic carbenes?, CHEMICAL SCIENCE, 6, 1895, (2015)
Abstract: The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the pi-accepting ability of NHCs, independent of their sigma-donating ability, via the collection of Se-77 or P-31 NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that delta(Se) is correlated to the energy gap between a filled lone pair orbital on Se and the empty pi* orbital corresponding to the Se-NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital pi-contribution to bonding and the chemical shielding, while a good correlation was found between the pi-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept pi-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between delta(Se) and delta(P) and pi-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.
First author: Witwicki, M, Understanding natural semiquinone radicals – Multifrequency EPR andg relativistic DFT studies of the structure of Hg(II) complexes, CHEMOSPHERE, 119, 479, (2015)
Abstract: Multifrequency EPR spectroscopy and DFT calculations were used to investigate Hg(II) complexes with semiquinone radical ligands formed in a direct reaction between the metal ions and tannic acid (a polyphenol closely related to tannins). Because of the intricate structure of tannic acid a vast array of substituted phenolic compounds were tested to find a structural model mimicking its ability to react with Hg(II) ions. The components of the g matrix (the g tensor) determined from the high field (208 GHz) EPR spectra of the Hg(II) complexes with the radical ligands derived from tannic acid and from the model compounds were analogous, indicating a similar coordination mode in all the studied Hg(II) complexes. Since catechol (1,2-dihydroxybenzene) was the simplest compound undergoing the reaction with Hg(II) it was selected for DFT studies which were aimed at providing an insight into the structural properties of the investigated complexes. Various coordination numbers and different conformations and protonation states of the ligands were included in the theoretical analyses. g Matrices were computed for all the DFT optimized geometries. A good agreement between the theoretical and experimental values was observed only for the model with the Hg(II) ion tetracoordinated by two ligands, one of the ligands being monoprotonated with the unpaired electron mainly localized on it.
First author: Deb, T, Scorpionato Halide Complexes [(Tp(Ph,Me))Ni-X] [X = Cl, Br, I; Tp(Ph,Me)g = Hydrotris(3-phenyl-5-methyl-1-pyrazolyl)-borate]: Structures,g Spectroscopy, and Pyrazole Adducts, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 119, 458, (2015)
Abstract: Pseudotetrahedral scorpionato halide complexes [(Tp(Ph,Me)) Ni-X] [Tp(Ph,Me) = hydrotris(3-phenyl-5-methyl-1-pyrazolyl) borate] were synthesized by metathesis of Tl(Tp(Ph,Me)) and NiX2 (X = Cl, Br, I). Pyrazole adducts [(Tp(Ph,Me)) Ni(Hpz(Ph,Me)) (X)] (X = Cl, I) were also obtained. [(Tp(Ph,Me)) Ni-X] (X = Br, I) are isomorphous with previously reported [(Tp(Ph,Me)) Ni-Cl], and a new solvated pseudo-polymorph [(Tp(Ph,Me))Ni-Cl]center dot 2CH(2)Cl(2) was found in this work. Ni-X bond lengths correspond to ionic radii of the halide ions, but some variations in Ni-Cl and Ni-N bond lengths are respectively attributed to bending of the chloride from the ideal threefold HB center dot center dot center dot Ni axis and to the size of the 3-pyrazole substituents. Electronic spectra were rationalized by means of time-dependent (TD) DFT calculations on simplified C-3v-symmetric [(Tp) Ni-X] models. Exogenous pyrazole binds to give the pentacoordinate adducts [(Tp(Ph,Me)) Ni(Hpz(Ph,Me))(X)] (X = Cl, I). We obtained a crystal structure of the iodide adduct, as well as that of [(Tp(Ph,Me)) Ni(Hpz(Ph,Me))(Cl)]center dot 0.5MeCN, isomorphous with a previously reported aquo monosolvate. A hallmark of adduct formation is an intramolecular N-H center dot center dot center dot X hydrogen bond between the added pyrazole and the adjacent halide ligand, thus giving rise to a strong IR absorption band. The stretching frequency correlates to the N(H)center dot center dot center dot X separation for the range of known adducts.
First author: Ruger, R, Efficient Calculation of Electronic Absorption Spectra by Means ofg Intensity-Selected Time-Dependent Density Functional Tight Binding, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 11, 157, (2015)
Abstract: During the last two decades density functional based linear response approaches have become the de facto standard for the calculation of optical properties of small and medium-sized molecules. At the heart of these methods is the solution of an eigenvalue equation in the space of single-orbital transitions, whose quickly increasing number makes such calculations costly if not infeasible for larger molecules. This is especially true for time-dependent density functional tight binding (TD-DFTB), where the evaluation of the matrix elements is inexpensive. For the relatively large systems that can be studied the solution of the eigenvalue equation therefore determines the cost of the calculation. We propose to do an oscillator strength based truncation of the single-orbital transition space to reduce the computational effort of TD-DFTB based absorption spectra calculations. We show that even a sizeable truncation does not destroy the principal features of the absorption spectrum, while naturally avoiding the unnecessary calculation of excitations with small oscillator strengths. We argue that the reduced computational cost of intensity-selected TD-DFTB together with its ease of use compared to other methods lowers the barrier of performing optical properties calculations of large molecules, and can serve to make such calculations possible in a wider array of applications.
First author: Benz, F, Nanooptics of Molecular-Shunted Plasmonic Nanojunctions, NANO LETTERS, 15, 669, (2015)
Abstract: Gold nanoparticles are separated above a planar gold film by 1.1 nm thick self-assembled molecular monolayers of different conductivities. Incremental replacement of the nonconductive molecules with a chemically equivalent conductive version differing by only one atom produces a strong 50 nm blue-shift of the coupled plasmon. With modeling this gives a conductance of 0.17G0 per biphenyl-4,4′-dithiol molecule and a total conductance across the plasmonic junction of 30G0. Our approach provides a reliable tool quantifying the number of molecules in each plasmonic hotspot, here <200.
First author: Abdoul-Carime, H, Solution vs. gas phase relative stability of the choline/acetylcholineg cavitand complexes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 4448, (2015)
Abstract: How the information obtained from the gas phase experiments can reflect the processes in solution is a crucial question for analytical chemistry, and particularly the selective host-guest recognition mechanisms which are fundamental in biology. Here we combine ElectroSpray Ionization mass spectrometry (ESI-MS) and the Collision Induced Dissociation (CID) experiments to the density functional theory to investigate the interaction of acetylcholine and the choline cation with a triphosphonate cavitand. While the relative abundance of the cation complexes in the ESI mass spectrum reflects the preferential capture of the acetylcholine ion over the choline ion by the cavitand in the solution, the gas phase CID measurements indicate that after desolvation the choline cation is the most strongly bound to the host. The experimental results are interpreted by theory that underlines the role of the counterion in the stabilization of the complexes in solution and therefore in the selective recognition of substrates of biological interest.
First author: Ulloa, CO, [2.2.2]Paracyclophane, preference for eta(6) or eta(18) coordinationg mode including Ag(I) and Sn(II): a survey into the cation-pi interactiong nature through relativistic DFT calculations, RSC ADVANCES, 5, 7803, (2015)
Abstract: [2.2.2] Paracyclophane is a versatile pi-cryptating structure, which can exhibit eta(2):eta(2):eta(2) and eta(6):eta(6):eta(6) coordination with metal ions, involving two or six carbon atoms in each aromatic ring. According to the nature of the metallic cation, the interaction can occur at the centre of the cage or upper face of the structure, which is determined mainly by the ligand-to-metal charge transfer ruled by symmetry and energetic considerations, and thus by the nature of the cation-pi interaction. For Ag(I), the 5s-Ag shell is close in energy to the frontier orbitals of paracyclophane, resulting in the formation of a bonding combination with the symmetric combination of the pi(2)-type levels, which leads to a non-centered conformation. In contrast, the Sn(II) case exhibits a largely favourable bonding interaction with the pi(2) and pi(3) type levels, which involve the 5p-Sn shell and result in a centered conformation. The interaction between the metal and paracyclophane was studied via molecular orbitals diagram, energy decomposition analyses (EDA) and non-covalent indexes (NCI).
First author: Ferbinteanu, M, Metal-Organic Frameworks with d-f Cyanide Bridges: Structural Diversity,g Bonding Regime, and Magnetism, LANTHANIDE METAL-ORGANIC FRAMEWORKS, 163, 185, (2015)
Abstract: We present a selection of metal-organic frameworks based on d-f and f-f linkages, discussing their structural features and properties from experimental and theoretical viewpoints. We give an overview of our own synthetic and modeling methodologies, highlighting the complexity of the interdisciplinary approach developed. Significant experimental and computational strategies of other researchers are also reviewed. The bonding regime of lanthanide units in MOFs is similar to those encountered in mono-or polynuclear f-type coordination compounds. However, the steric demands of constructing a three-dimensional network determine specific ligand composition and topologies at the local f nodes. Due to weak interaction propensity of the inner shell f orbitals, the electronic structure treatments of lanthanide units require certain conceptual and technical subtleties. With proper handling, multiconfiguration wave function approaches as well as density functional theory (DFT) treatments can be analyzed in terms of meaningful ligand field (LF) modeling. The interplay of LF and spin-orbit (SO) effects in determining the magnetic anisotropy is illustrated, after reviewing the experimental magnetic behavior of several d-f cyanide-bridged systems.
First author: Gianetti, TL, Electron localization in a mixed-valence diniobium benzene complex, CHEMICAL SCIENCE, 6, 993, (2015)
Abstract: Reaction of the neutral diniobium benzene complex {[Nb(BDI)(NBu)-Bu-t](2)(mu-C6H6)} (BDI = N, N'-diisopropylbenzene- beta-diketiminate) with Ag[B(C6F5) 4] results in a single electron oxidation to produce a cationic diniobium arene complex, {[Nb(BDI)(NBu)-Bu-t](2)(mu-C6H6)}{B(C6F5)(4)}. Investigation of the solid state and solution phase structure using single-crystal X-ray diffraction, cyclic voltammetry, magnetic susceptibility, and multinuclear NMR spectroscopy indicates that the oxidation results in an asymmetric molecule with two chemically inequivalent Nb atoms. Further characterization using density functional theory (DFT) calculations, UV-visible, Nb L-3,L-2-edge X-ray absorption near-edge structure (XANES), and EPR spectroscopies supports assignment of a diniobium complex, in which one Nb atom carries a single unpaired electron that is not largely delocalized on the second Nb atom. During the oxidative transformation, one electron is removed from the delta-bonding HOMO, which causes a destabilization of the molecule and formation of an asymmetric product. Subsequent reactivity studies indicate that the oxidized product allows access to metal-based chemistry with substrates that did not exhibit reactivity with the starting neutral complex.
First author: Hering, F, Bite-angle bending as a key for understanding group-10 metal reactivityg of d(10)-[M(NHC)(2)] complexes with sterically modest NHC ligands, CHEMICAL SCIENCE, 6, 1426, (2015)
Abstract: Synthesis, characterization and investigations on the reactivity of the novel metal basic, yet isolable 14 VE NHC-complexes [M-0(iPr(2)Im)(2)] (M = Pd 3, Pt 4; iPr(2)Im = 1,3-di-isopropyl-imidazolin-2-ylidene; VE = valence electron; NHC = N-heterocyclic carbene) is reported and compared to the chemistry of the corresponding nickel complex. Quantum chemical analyses reveal that differences in the reactivity of group 10 NHC complexes are caused by differences in the rigidity and thus activation strain associated with bending the corresponding d(10)-[M(NHC)(2)] fragments during reaction. These results should have implications for the understanding of the fundamental steps in catalytic cycles, in which such complex fragments are employed.
First author: Funes, AV, Switching nuclearity and Co(II) content through stoichiometryg adjustment: {(Co6Co3III)-Co-II} and {(CoCo4III)-Co-II} mixed valentg complexes and a study of their magnetic properties, DALTON TRANSACTIONS, 44, 2390, (2015)
Abstract: We are reporting two new mixed valent Co(II)/Co(III) polynuclear complexes, {(Co6Co3III)-Co-II} and {(CoCo4III)-Co-II}, bearing different amount of Co(II) ions in their cores, through the employment of the multidentate triethanolamine (teaH(3)) ligand in different stoichiometric ratios. We present a complete picture of the magnetic behaviour of both complexes through a combined usage of the susceptibility, magnetization and X-band EPR data as well as broken-symmetry DFT calculations. Compound 1 shows an atypical spin-only behaviour, probably due to the presence of four and five coordinated Co(II) sites as well as highly distorted six coordinated Co(II) ions, promoting a high degree of orbital contribution quenching. Through the usage of a simplified exchange coupling scheme and relying on DFT based magneto-structural correlation we have been able to explain the observed diamagnetic ground state. Concerning compound 2, DC magnetic data supported by X-band EPR measurements suggest the existence of anisotropy with a zero-field splitting parameter D, at least in the range of 2-10 cm(-1). In agreement with this description, a slow relaxation of magnetization is observed after applying a small external magnetic field, under AC measurements. Field and temperature dependence of the characteristic relaxation time establishes a thermal barrier for magnetization reversal of about 25 cm(-1), which is in good agreement with the energy splitting of the vertical bar ± 1/2 > and vertical bar ± 3/2 > doublets established from static magnetic measurements.
First author: Lv, CM, Tuning electronic structures of uranyl fluorides via increasingg equatorial pyridyl number and extending pyridyl conjugation, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1051, 144, (2015)
Abstract: Uranyl complexes, [(UO2)(PY)F-4](2)-(1a, PY = pyridine), [(UO2)(Py)(3)(cis-F)(2)] (1a9, RUO2)(PY)sl2+ (la"), KUO2)(bPY)F3r (2a, bPY = 2,2′-bipyridine), P02)(tpy)F21 (3a, tpy = 2,2′:6'2″-terpyridine) and [(UO2) (qpy)Fr (4a, qpy = 2,2′:6′,2″:6″,2″-quaterpyridine) have been examined using scalar relativistic density functional theory (DFT). It is shown that both increasing the monopyridyl number (from la to la' and la") and extending the pyridyl conjugation (from la to 2a, 3a and 4a) are capable of tuning electronic structures of uranyl complexes. Unlike those of la, for instance, 4a is featured with n(qpy) character of HOMO and HOMO-1, and its cr(U=0) bond is greatly stabilized to form HOMO-2; and more it*(qpy)-type orbitals insert between U(f)-based and n*(U=-0) unfilled orbitals. For comparison, fourfold uranyl complexes with one less equatorial fluorine ligand ([(UO2)(py)F3r (1b), [(UO2)(bpy)F21 (2b), I(UO2)(tpy)Fr (3b) and RUO2)(cIPY)12* (411)) were calculated. Both thermodynamic and geometrical results suggest that polypyridyl (such as bpy, tpy and qpy) dioxouranium complexes favor fivecoordinated mode in the equatorial plane, whereas fourfold is preferred by the single-pyridyl complex.
First author: Hazlehurst, RJ, Oxidation of dimethylplatinum(II) complexes with malonyl peroxideg derivatives, CANADIAN JOURNAL OF CHEMISTRY, 93, 74, (2015)
Abstract: The reaction of the cyclic peroxides cyclobutane malonoyl peroxide and cyclopentane malonoyl peroxide to dimethylplatinum( II) complexes with the bidentate nitrogen donor ligand 4,4′-di-t-butyl-2,2′-bipyridine (bubpy) gave a mixture of the products of cis and trans oxidative addition, [PtMe2{(O2C2)(2)C(C3H6)}(bubpy)] and [PtMe2{(O2C)(2)C(C4H8)}(bubpy)], respectively. The cis isomers exist with a chelating dicarboxylate ligand, forming a six-membered ring, while the trans isomers are thought to exist as oligomers, which may react with water or solvent to give complexes containing a monodentate dicarboxylate ligand. Equilibration of the product of cis oxidative addition, cis-[PtMe2{(O2C)(2)C(C3H6)}(bubpy)], with oxalic or phthalic acid to give equilibria with the oxalate cis-[PtMe2(O4C2)(bubpy)] or phthalate cis-[PtMe2{(O2C)(2)C6H4}(bubpy)] derivative, respectively, indicated the expected sequence of chelate stability oxalate > cyclobutane malonate > phthalate.
First author: Conradie, J, Density functional theory calculations of Rh-beta-diketonato complexes, DALTON TRANSACTIONS, 44, 1503, (2015)
Abstract: Density functional theory (DFT) results on the geometry, energies and charges of selected Rh-beta-diketonato reactants, products and transition states are discussed. Various DFT techniques are used to increase our understanding of the orientation of ligands coordinated to Rh, to identify the lowest energy geometry of possible geometrical isomers and to get a molecular orbital understanding of ground and transition states. Trends and relationships obtained between DFT calculated energies and charges, experimentally measured values and electronic parameters describing the electron donating power of groups and ligands, enable the design of ligands and complexes of specific reactivity.
First author: Caramori, GF, Cyclic trinuclear copper(I), silver(I), and gold(I) complexes: ag theoretical insight, DALTON TRANSACTIONS, 44, 377, (2015)
Abstract: The metal-ligand, M-L, bonding situation in cyclic trinuclear complexes, CTCs, of copper(I), silver(I), and gold(I) was investigated in terms of the energy decomposition analysis (EDA-NOCV) and natural bond orbitals (NBOs). The anisotropy of the induced current density (ACID) and magnetic response were employed to evaluate the effect of electronic conjugation and metal-metal interactions in CTCs. The EDA-NOCV results show that the M-L bonding is stronger in gold(I) than in copper(I) or silver(I) complexes. Au+-L bonds present an elevated covalent character when compared with Cu+-L and Ag+-L bonds. The NBO analysis confirms the elevated covalent character observed for Au+-L bonds, indicating that the ligand-metal donation, L -> M, and the metal-ligand back-donation, M -> L, are more stabilizing in gold(I) than in copper(I) or silver(I) complexes. Both ACID and the magnetic response calculations reveal that there are cyclic conjugations in the ligands and a strong diatropic ring current indicating the presence of aromaticity. However, there is no through-bond M-L conjugation between the ligands and the metallic centers, as indicated by the absence of a continuous anisotropy boundary surface involving M-L bonds.
First author: Azam, M, Novel uranyl(VI) complexes incorporating propylene-bridged salen-typeg N2O2-ligands: a structural and computational approach, DALTON TRANSACTIONS, 44, 568, (2015)
Abstract: The synthesis of the tetradentate dianionic ligand, H2L (2,2′-(1E,1'E)-(2,2-dimethylpropane-1,3-dyl)bis(azanylylidene)bis(methanylylidene)diphenol), from 2,2-dimethyl-1,3-diaminopropane and its reaction with UO2(CH3COO)(2)center dot 2H(2)O in a 1 : 1 molar ratio in methanol to produce the complex [UO2(L)(CH3OH)] are reported. The isolated compounds have been characterized by elemental analysis, ionization mass spectrometry (ESI-MS), UV/Vis, FT-IR, H-1- and C-13-NMR, DEPT-135 spectroscopy, TGA and single-crystal X-ray diffraction. As shown by X-ray crystallography, the coordination geometry around the uranium centre is distorted pentagonal bipyramidal with two imine nitrogen atoms, two phenolic oxygen atoms and one methanol O atom occupying equatorial sites, together with two axial oxo groups. To obtain insights into the structure and spectral properties of the studied complex, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations have been carried out. The computed results show that LUMO of the complex is featured with uranium f orbital character. TD-DFT results indicate that the complex displays two intense bands and one weak charge transfer band. The charge transfer band is primarily due to HOMO. LUMO (53%). Two intense bands have main contributions from HOMO-2 -> LUMO (81%) and HOMO-3 -> LUMO (77%) transitions, respectively. TD-DFT results indicate that the complex displays the charge transfer band primarily due to HOMO. LUMO (53%) and other two charge transfer bands have main contributions from HOMO-2 -> LUMO (81%), HOMO-3 -> LUMO (77%) transitions, respectively. NBO analysis reveals that the ground state of the complex is mainly stabilized by n -> n* interaction. EDA analysis reveals that the interaction existing between the ligand and other parts of the complex is mainly electrostatic in nature.
First author: Martin-Somer, A, Acidity enhancement of unsaturated bases of group 15 by association withg borane and beryllium dihydride. Unexpected boron and beryllium Bronstedg acids, DALTON TRANSACTIONS, 44, 1193, (2015)
Abstract: The intrinsic acidity of CH2=CHXH2, HC equivalent to CXH2 (X = N, P, As, Sb) derivatives and of their complexes with BeH2 and BH3 has been investigated by means of high-level density functional theory and molecular orbital ab initio calculations, using as a reference the ethyl saturated analogues. The acidity of the free systems steadily increases down the group for the three series of derivatives, ethyl, vinyl and ethynyl. The association with both beryllium dihydride and borane leads to a very significant acidity enhancement, being larger for BeH2 than for BH3 complexes. This acidity enhancement, for the unsaturated compounds, is accompanied by a change in the acidity trends down the group, which do not steadily decrease but present a minimum value for both the vinyl- and the ethynyl-phosphine. When the molecule acting as the Lewis acid is beryllium dihydride, the pi-type complexes in which the BeH2 molecules interact with the double or triple bond are found, in some cases, to be more stable, in terms of free energies, than the conventional complexes in which the attachment takes place at the heteroatom, X. The most important finding, however, is that P, As, and Sb ethynyl complexes with BeH2 do not behave as P, As, or Sb Bronsted acids, but unexpectedly as Be acids.
First author: Manna, D, Actinide selectivity of 1,10-phenanthroline-2,9-dicarboxamide and itsg derivatives: a theoretical prediction followed by experimentalg validation, DALTON TRANSACTIONS, 44, 1332, (2015)
Abstract: The conventional concept of selective complexation of actinides with soft donor ligands (either S or N donor) has been modified here through exploiting the concept, "intra-ligand synergism", where a hard donor atom, such as oxygen preferentially binds to trivalent actinides [An(III)] as compared to the valence iso-electronic trivalent lanthanides [Ln(III)] in presence of another soft donor centre. We have theoretically predicted the selectivity of 1,10-phenanthroline-2,9-dicarboxylamide towards the Am(III) ion through density functional calculations. Subsequently, several such amide derivatives have been synthesized to optimize the solubility of the ligands in the organic phase. Finally, solvent extraction experiments have been carried out to validate our theoretical prediction on the selectivity of mixed donor ligands towards Am(III) as compared to Eu(III), and a maximum separation factor of about 51 has been achieved experimentally using the 2,9-bis(N-decylaminocarbonyl)-1,10-phenanthroline ligand.
First author: Niebel, C, Thienoacene dimers based on the thieno[3,2-b] thiophene moiety:g synthesis, characterization and electronic properties, JOURNAL OF MATERIALS CHEMISTRY C, 3, 674, (2015)
Abstract: Two thienoacene dimers based on the thieno[3,2-b] thiophene moiety were efficiently synthesized, characterized and evaluated as active hole-transporting layers in organic thin-film field-effect transistors. Both compounds behaved as active p-channel organic semi-conductors showing averaged hole mobility of up to 1.33 cm(2) V-1 s(-1).
First author: Pan, S, Metastable behavior of noble gas inserted tin and lead fluorides, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 972, (2015)
Abstract: Ab initio computations are carried out to explore the structure and stability of FNgEF(3) and FNgEF (E = Sn, Pb; Ng = Kr-Rn) compounds. They are the first reported systems to possess Ng-Sn and Ng-Pb bonds. Except for FKrEF3, the dissociations of FNgSnF(3) and FNgEF, producing Ng and SnF4 or EF2, are only exergonic in nature at room temperature, whereas FNgPbF(3) has a thermochemical instability with respect to two two-body dissociation channels. However, they are kinetically stable, having positive activation barriers (ranging from 2.2 to 49.9 kcal mol(-1)) with respect to those dissociations. The kinetic stability gradually improves in moving from the Kr to Rn analogues. The remaining possible dissociation channels for these compounds are found to be endergonic in nature. The nature of the bonding is analyzed by natural bond order, electron density, and energy decomposition analyses. Particularly, the natural population analysis reveals that they are best represented as F-(NgEF(3))(+) and F-(NgEF)(+). All the Xe/Rn-E bonds in FNgEF(3) and FNgEF are covalent in nature.
First author: Wolters, LP, Covalency in resonance-assisted halogen bonds demonstrated withg cooperativity in N-halo-guanine quartets, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 1585, (2015)
Abstract: Halogen bonds are shown to possess the same characteristics as hydrogen bonds: charge transfer, resonance assistance and cooperativity. This follows from the computational analyses of the structure and bonding in N-halo-base pairs and quartets. The objective was to achieve an understanding of the nature of resonance-assisted halogen bonds (RAXB): how they resemble or differ from the better understood resonance-assisted hydrogen bonds (RAHB) in DNA. We present an accurate physical model of the RAXB based on the molecular orbital theory, which is derived from the corresponding energy decomposition analyses and study of the charge distribution. We show that the RAXB arise from classical electrostatic interaction and also receive strengthening from donor-acceptor interactions within the sigma-electron system. Similar to RAHB, there is also a small stabilization by pi-electron delocalization. This resemblance leads to prove cooperativity in N-halo-guanine quartets, which originates from the charge separation that occurs with donor-acceptor orbital interactions in the s-electron system.
First author: Li, JB, SO2 – yet another two-faced ligand, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 1987, (2015)
Abstract: Experimentally known adducts of SO2 with transition metal complexes have distinct geometries. In the present paper, we demonstrate by a bonding analysis that this is a direct consequence of sulfur dioxide acting as an acceptor in one set, square-planar complexes of d(8) and linear two-coordinated complexes of d(10) transition metals, and as a donor with other compounds, well-known paddle-wheel [Rh-2(O2CCF3)(4)] and square-pyramidal [M(CO)(5)] (M = Cr, W) complexes. Bonding energy computations were augmented by the natural bond orbital (NBO) analysis and energy decomposition analysis (EDA). When the SO2 molecule acts as an acceptor, bonding in the bent coordination mode to the axial position of the d(8) or the d(10) metal center, the dominant contributor to the bonding is LAO(S) (Lewis Acidic Orbital, mainly composed of the px-orbital of the S atom) as an acceptor, while a d(z)(2) orbital centered on the metal is the corresponding donor. In contrast, the distinct collinear (or linear) coordination of the SO2 bound at the axial position of [Rh-2(O2CCF3)(4)] and/or [M(CO)(5)] is associated with a dominant donation from a lone pair localized on the sulfur atom, sigma*(Rh-Rh) and/or empty LAO(M) (mainly composed of the d(z)(2) orbital of the metal), respectively, acting as an acceptor orbital. The donor/acceptor capabilities of the SO2 molecule were also checked in adducts with organic Lewis acids (BH3, B(CF3)(3)) and Lewis bases (NH3, N(CH3)(3), N-heterocyclic carbene).
First author: Braunschweig, H, Stepwise isolation of low-valent, low-coordinate Sn and Pb mono- andg dications in the coordination sphere of platinum, CHEMICAL SCIENCE, 6, 425, (2015)
Abstract: Synthetic access to low-coordinate Pb mono- and dications is in general impeded due to their poor solubility and highly electrophilic nature. However, the electrophilicity of these cations can be tamed by attaching them to electron-rich transition metals. Following this principle we have isolated low-valent Pb mono- ([(Cy3P)(2)Pt-PbCl](2)[AlCl4](2), 8a) and dications ([(Cy3P)(2)Pt(Pb)][AlCl4](2), 11) in the coordination sphere of platinum. The same approach then has been implemented for the isolation of analogous low-valent Sn mono- (7a) and dications (10). An energy decomposition analysis (EDA-NOCV) was performed to investigate the nature of Pt-Pb and Pb-Cl bonding in [(Cy3P)(2)Pt(PbCl2)] (2), 8a and 11. The results show that the Pt-Pb bonds in 8a and 11 are electron-sharing in nature, whereas that of the precursor 2 is a dative bond. The breakdown of attractive interactions in 2, 8a and 11 reveals that the ionic interactions in the analyzed Pt-Pb and Pb-Cl bonds are always stronger than the covalent interactions, except for the Pb-Cl bond in 8a. The calculated D3 dispersion energies show that dispersion interactions play a key role in the thermodynamic stability of 2, 8a and 11.
First author: Mulet-Gas, M, Small endohedral metallofullerenes: exploration of the structure andg growth mechanism in the Ti@C-2n (2n=26-50) family, CHEMICAL SCIENCE, 6, 675, (2015)
Abstract: The formation of the smallest fullerene, C-28, was recently reported using gas phase experiments combined with high-resolution FT-ICR mass spectrometry. An internally located group IV metal stabilizes the highly strained non-IPR C-28 cage by charge transfer (IPR = isolated pentagon rule). Ti@C-44 also appeared as a prominent peak in the mass spectra, and U@C-28 was demonstrated to form by a bottom-up growth mechanism. We report here a computational analysis using standard DFT calculations and Car-Parrinello MD simulations for the family of the titled compounds, aiming to identify the optimal cage for each endohedral fullerene and to unravel key aspects of the intriguing growth mechanisms of fullerenes. We show that all the optimal isomers from C-26 to C-50 are linked by a simple C-2 insertion, with the exception of a few carbon cages that require an additional C-2 rearrangement. The ingestion of a C-2 unit is always an exergonic/exothermic process that can occur through a rather simple mechanism, with the most energetically demanding step corresponding to the closure of the carbon cage. The large formation abundance observed in mass spectra for Ti@C-28 and Ti@C-44 can be explained by the special electronic properties of these cages and their higher relative stabilities with respect to C-2 reactivity. We further verify that extrusion of C atoms from an already closed fullerene is much more energetically demanding than forming the fullerene by a bottom-up mechanism. Independent of the formation mechanism, the present investigations strongly support that, among all the possible isomers, the most stable, smaller non-IPR carbon cages are formed, a conclusion that is also valid for medium and large cages.
First author: Jensen, KR, ANALYTICAL APPLICATIONS OF ELECTRON MONOCHROMATOR-MASS SPECTROMETRY, MASS SPECTROMETRY REVIEWS, 34, 24, (2015)
Abstract: An electron monochromator (EM) produces an electron beam with a narrow energy distribution that can be utilized with mass spectrometry (MS). The history and development of the EM from an initial research design to a commercial model are reviewed along with MS research applications. An EM incorporated with a mass spectrometer showed significant improvement in sensitivity over traditional methods for negative-ion generation and selectivity for compounds with electrophilic character. Sensitivity of EM-MS has been shown to be 25fg for hexachlorobenzene in positive-ion mode and 10fg for nitrobenzene in negative-ion mode. Reports regarding the analysis of chlorinated compounds, explosives, pesticides, phthalates, polychlorodibenzo-p-dioxins, polycyclic aromatic hydrocarbons (PAHs), nitro-polycyclic aromatic hydrocarbons (NPAHs), antioxidants, and bacterial biomarkers are discussed. Additionally, theoretical methods to predict electron-capture properties are presented. (c) 2013 Wiley Periodicals, Inc. Mass Spec Rev 34: 24-42, 2015.
First author: Pignotti, LR, Bimetallic nickel complexes supported by 2,5-bis(g phosphine)-1,4-hydroquinonate ligands. Structural, electrochemical andg theoretical investigations, INORGANICA CHIMICA ACTA, 424, 274, (2015)
Abstract: The coordination chemistries of several 2,5-bis(phosphine)-1,4-hydroquinones, (2,5-bis(PiPr(2))-3, 6-difluoro-1,4-hydroquinone (1a), 2,5-bis(PiPr(2))-1,4-hydroquinone (1b), (2,5-bis(PPh2)-3,6-difluoro-1,4-hydroquinone (1c), and 2,5-bis(PPh2)-1,4-hydroquinone (1d)) were investigated. Reactions of these ligands 1a-d with excess (similar to 2.5) of bis(cyclopentadienide) nickel, and in case of 1a, with bis(pentamethylcyclopentadienide) nickel, resulted in the formation of bimetallic nickel complexes 2a-d and 3a, where both [P,O] chelating pockets of the ligands were occupied by CpNi or Cp*/Ni moieties, respectively. Cyclic voltammetric (CV) scans on complexes 2a-d contained a common feature of two reversible/quasi-reversible waves and one irreversible redox event. Complex [2a][PF6] was isolated by the oxidation of 2a with ferrocenium hexafluorophosphate. Spectroscopic, structural, and synthetic studies were carried out in order to elucidate the nature of these redox processes. Our results suggest that the reversible and quasi-reversible redox events are ligand-based processes (hydroquinone/semiquinone/quinone), while the irreversible process was assigned as metal-based. These conclusions were supported by additional experimental data and by theoretical calculations. Investigations of chemical reactivity showed that cyclopentadienide ligands in complexes 2a-d can be displaced from the metal centers upon reactions with o-aminothiophenol. One of these derivatives, 4a, containing capping [N,S] o-aminothiophenolate ligands was isolated and fully characterized. A CV scan of complex 4a contained one reversible wave and an irreversible wave at higher potentials. The assignment is complicated by the proton transfer processes accompanying the electron transfer events. Complexes 1a, 2a-c, [2a][PF6] and 4a were characterized by single crystal X-ray diffraction experiments.
First author: Arcisauskaite, V, Structure and bonding in trimetallic arrays containing a Cr-Cr quadrupleg bond: A challenge to density functional theory, INORGANICA CHIMICA ACTA, 424, 293, (2015)
Abstract: Structural trends within the series of trimetallics Cr2M(dpa)(4)Cl-2, M = Cr, Mn, Fe, Ni and Zn offer an important test bed for the theoretical treatment of the quadruple Cr-Cr bond. Cr-Cr bond lengths are dramatically functional dependent, reflecting the different treatment of exchange and correlation in each case. The presence of a paramagnetic heterometal in a Cr2M(dpa)(4)Cl-2 array has the effect of elongating the Cr-Cr bond by polarising the spin density in the Cr-Cr sigma bond, effectively seeding the localisation of the remaining pi and delta components.
First author: Van Dorn, LO, From gas-phase ionization energies to solution oxidation potentials:g Dimolybdenum tetraformamidinate paddlewheel complexes, INORGANICA CHIMICA ACTA, 424, 316, (2015)
Abstract: The gas-phase ionization energies of a series of Mo-2(DPhF)(4) paddlewheel complexes (DPhF is the N,N'-diphenylformamidinate anion with p-CH3, p-Cl, m-Cl, p-CF3, or m-CF3 phenyl substituents) have been measured by ultraviolet photoelectron spectroscopy (UPS) and compared with the solution oxidation potentials measured by cyclic voltammetry (CV) reported by Ren and coworkers. A linear relationship was found between the gas-phase ionization energies and the solution oxidation potentials. Density functional theory (DFT) computations clarify the individual electronic and thermodynamic factors that contribute to the correlation. The metal-metal delta bond electron energy is the largest factor in determining the solution oxidation potential. The substituents shift the metal-metal orbital energies by changing the through-space field potential at the metals rather than by an inductive change in charge at the metals or orbital overlap effects. The cation solvation energies determine the extent that the potential shifts are attenuated in solution. The results show that substituent field effects and solvation have major roles in determining the dimetal redox chemistry even when the dimetal unit is protected from direct interaction with the substituent and the solvent.