A Tail Does Not Always Make a Difference: Assembly of cds Nets from Co(NCS)2 and 1,4-bis(n-Alkyloxy)-2,5-bis(3,2′:6′,3″-terpyridin-4′-yl)benzene Ligands

The consistent assembly of a (65.8) cds net is observed in reactions of cobalt(II) thiocyanate with 1,4-bis(n-alkyloxy)-2,5-bis(3,2′:6′,3″-terpyridin-4′-yl)benzene ligands in which the n-alkyloxy substituents are n-propyl (ligand 3), n-butyl (4), n-pentyl (5), n-hexyl (6), n-heptyl (7), and n-octyl (8). Crystals were grown by layering a methanol solution of Co(NCS)2 over a 1,2-dichlorobenzene solution of each ligand. The choice of crystallization solvents is critical in directing the assembly of the cds net. Single-crystal structures of [Co(NCS)2(3)]n.3.5nC6H4Cl2, [Co(NCS)2(4)]n.5.5nC6H4Cl2, [Co(NCS)2(5)]n.4nC6H4Cl2, [Co(NCS)2(6)]n.3.8nC6H4Cl2, [Co(NCS)2(7)]n.3.1nC6H4Cl2, and [Co(NCS)2(8)]n.1.6nC6H4Cl2.2nMeOH (C6H4Cl2 = 1,2-dichlorobenzene) are presented and compared. The n-alkyloxy chains exhibit close to extended conformations and are accommodated in cavities in the lattice without perturbation of the coordination framework.

Yoshida et al. [15] were the first to report the coordination chemistry of tetratopic ligands combining two divergent terpyridine domains; this included ligand 2 (Scheme 1). In addition to the conformational flexibility described in Scheme 2, ligands such as 2 also exhibit conformational variation arising from bond rotation about the arene spacer-tpy C-C bonds. With reference to the centroid of the central arene ring in 2 and the four outer pyridine N-donors, the ligand is described as a 4-connecting node, and the limiting geometries are defined with the two 3,2 :6 ,3 -tpy units being coplanar or orthogonal [16].

Crystal Growth Conditions
We have previously reported the synthesis and characterization of compounds 3-8.
Crystal growth experiments were carried out under ambient conditions (ca. 22 • C) by layering a MeOH solution of Co(NCS) 2 over a 1,2-Cl 2 C 6 H 4 solution of each ligand. Reactions were carried out on the same scale with the same concentrations of solutions, and X-ray quality crystals were obtained in periods ranging from 21 days to two months (see Section 3).

Single Crystal Structures
The compounds [Co(NCS) 2  2nMeOH crystallized in the monoclinic space group P2 1 /n. All six compounds exhibit similar, extended structures and we therefore discuss them together. The structures of the asymmetric units with atom numbering are shown in Figures S1-S6 in the Supporting Material. Each bis(3,2 :6 ,3 -tpy) ligand binds to four different {Co(NCS) 2 } units and therefore functions as a 4-connecting node. Each Co(II) center is 6-coordinate and is in a trans-{Co(NCS) 2 (N) 4 } environment, coordinated by four different bis(3,2 :6 ,3 -tpy) ligands. Thus, each Co(II) is also a 4-connecting node. Figure 1 illustrates this for [Co(NCS) 2 (3)] n . 3.5nC 6 H 4 Cl 2 as representative of the six structures. Selected bond parameters are given in Table 1; the Co-N bond lengths are unexceptional, and the N -Co-N bond angles are all close to 90 • , consistent with a regular octahedral coordination sphere.  The asymmetric unit in each of the structures of the complexes containing 3, 5, 6, 7 and 8 contains half of one independent ligand, with the second half being generated by inversion (Figures S1 and S3-S6 in the Supporting Material). Thus, symmetry dictates that the four N-donors are coplanar. In [Co(NCS)2(4)]n . 5.5nC6H4Cl2, the asymmetric unit contains one whole and one-half independent ligands. For the latter, the ligand is completed by inversion and so, again, the four N-donors (N7, N9, N7 i , N9 i in Figure S2) are coplanar. For the crystallographically independent ligand containing N1, N2, N3 and N4 ( Figure  S2), the angle between the plane containing N1, N2 and the centroid of the arene spacer, and the plane containing N3, N4 and the centroid of the arene ring, is 3.4°. This ligand is therefore also a planar, 4-connecting node, and while the ligands in [Co(NCS)2(4)]n . 5.5nC6H4Cl2 are crystallographically independent, they are topologically equivalent. Therefore, in all six structures, both the bis(3,2′:6′,3"-tpy) ligand and the cobalt center are planar, 4-connecting nodes and the assemblies propagate into 3D networks with a cds topology. This is one of the more common networks comprising planar 4-connecting nodes [27,28]; half of the adjacent nodes are coplanar and half are mutually perpendicular. This is shown for [Co(NCS)2(3)]n . 3.5nC6H4Cl2 in Figure 2, in which the ligand and metal nodes are shown in red and blue, respectively. The coordination networks with 3-8 are structurally related to that in [Co(NCS)2(9)]n . 1.6nH2O . 1.2nC6H4Cl2, crystals of which were also grown using a MeOH/1,2-Cl2C6H4 mixture [20]. The cds net was also found for [Co(NCS)2(12)]n . 2nC6H4Cl2 (see Scheme 3 for ligand 12) in which 12 is an isomer of 3 [29]. H atoms and solvent molecules are omitted for clarity. The asymmetric unit in each of the structures of the complexes containing 3, 5, 6, 7 and 8 contains half of one independent ligand, with the second half being generated by inversion (Figures S1 and S3-S6 in the Supporting Material). Thus, symmetry dictates that the four N-donors are coplanar. In [Co(NCS) 2 (4)] n . 5.5nC 6 H 4 Cl 2 , the asymmetric unit contains one whole and one-half independent ligands. For the latter, the ligand is completed by inversion and so, again, the four N-donors (N7, N9, N7 i , N9 i in Figure S2) are coplanar. For the crystallographically independent ligand containing N1, N2, N3 and N4 ( Figure S2), the angle between the plane containing N1, N2 and the centroid of the arene spacer, and the plane containing N3, N4 and the centroid of the arene ring, is 3.4 • . This ligand is therefore also a planar, 4-connecting node, and while the ligands in [Co(NCS) 2 (4)] n . 5.5nC 6 H 4 Cl 2 are crystallographically independent, they are topologically equivalent. Therefore, in all six structures, both the bis(3,2 :6 ,3 -tpy) ligand and the cobalt center are planar, 4-connecting nodes and the assemblies propagate into 3D networks with a cds topology. This is one of the more common networks comprising planar 4-connecting nodes [27,28]; half of the adjacent nodes are coplanar and half are mutually perpendicular. This is shown for [Co(NCS) 2 (3)] n . 3.5nC 6 H 4 Cl 2 in Figure 2, in which the ligand and metal nodes are shown in red and blue, respectively. The coordination networks with 3-8 are structurally related to that in [Co(NCS) 2 (9)] n . 1.6nH 2 O . 1.2nC 6 H 4 Cl 2 , crystals of which were also grown using a MeOH/1,2-Cl 2 C 6 H 4 mixture [20]. The cds net was also found for [Co(NCS) 2 (12)] n . 2nC 6 H 4 Cl 2 (see Scheme 3 for ligand 12) in which 12 is an isomer of 3 [29]. In each compound, the 3,2′:6′,3′′-tpy unit adopts conformation II (Scheme 2), an angles between the least-squares planes of bonded pairs of aromatic rings in the co nated ligands 3-8 show striking similarities ( Table 2). This is further demonstrated i overlay of one building block from each structure displayed in Figure 3. In each struc the n-alkyloxy chains are in close to extended conformations and it is noteworthy th increase in steric demands of the substituents has negligible effect on the overall stru as discussed below. Packing diagrams of the six structures with solvent molecules om are displayed in comparable orientations in Figure 4 and illustrate how the n-alky chains are accommodated in analogous cavities with little impact on the 3D framew The solvent-accessible void space was calculated using Mercury version 2022.1.0 [30] a contact surface map with probe radius of 1.2 Å . The decrease from 49.3% to 34.4% ( 3) is consistent with the increase in the steric demands of the n-alkyloxy chains.   In each compound, the 3,2 :6 ,3 -tpy unit adopts conformation II (Scheme 2), and the angles between the least-squares planes of bonded pairs of aromatic rings in the coordinated ligands 3-8 show striking similarities ( Table 2). This is further demonstrated in the overlay of one building block from each structure displayed in Figure 3. In each structure, the n-alkyloxy chains are in close to extended conformations and it is noteworthy that the increase in steric demands of the substituents has negligible effect on the overall structure as discussed below. Packing diagrams of the six structures with solvent molecules omitted are displayed in comparable orientations in Figure 4 and illustrate how the n-alkyloxy chains are accommodated in analogous cavities with little impact on the 3D framework. The solvent-accessible void space was calculated using Mercury version 2022.1.0 [30] with a contact surface map with probe radius of 1.2 Å. The decrease from 49.3% to 34.4% (Table 3) is consistent with the increase in the steric demands of the n-alkyloxy chains.

Bulk Sample Analysis
Powder X-ray diffraction (PXRD) and solid-state IR spectroscopy were used to analyze the bulk materials after single crystals had been selected for single-crystal X-ray diffraction. The IR spectra are shown in Figs. S7-S12, and a strong absorption at 2065, 2069, 2069, 2067, 2068 or 2056 cm -1 for the compound containing ligands 3, 4, 5, 6, 7 or 8,

Bulk Sample Analysis
Powder X-ray diffraction (PXRD) and solid-state IR spectroscopy were used to analyze the bulk materials after single crystals had been selected for single-crystal X-ray diffraction. The IR spectra are shown in Figures S7-S12, and a strong absorption at 2065, 2069, 2069,  2067, 2068 or 2056 cm −1 for the compound containing ligands 3, 4, 5, 6, 7 or 8, respectively, was assigned to the ν(CN) mode of the coordinated thiocyanato ligands. The fingerprint regions of the IR spectra are all similar.
For [Co(NCS) 2 (6)] n . 3.8nC 6 H 4 Cl 2 , an excellent fit was found between the experimental PXRD pattern for the bulk material and the pattern predicted from the single-crystal structure ( Figure 5). However, for the remaining compounds, good fits were not obtained, most likely because of solvent loss which occurs on standing at ambient temperatures. Overlays of the experimental PXRD (298 K) for the bulk material and that predicted from the single crystal structures (150 K) of [Co(NCS) 2 3.8nC6H4Cl2, an excellent fit was found between the experimenta PXRD pattern for the bulk material and the pattern predicted from the single-crystal struc ture ( Figure 5). However, for the remaining compounds, good fits were not obtained, mos likely because of solvent loss which occurs on standing at ambient temperatures. Overlays of the experimental PXRD (298 K) for the bulk material and that predicted from the single crystal structures (150 K) of [Co(NCS)2(3)]n . 3.5nC6H4Cl2 and [Co(NCS)2(4)]n . 5.5nC6H4Cl are shown in Figures S13 and S14.

Role of Solvents
The consistency of the cds net in the [Co(NCS) 2 (L)] n family for L = 3-8 and as well as 9 [20] when crystallization conditions are the same, and the appearance of other nets when different solvent systems are used [20,21] indicates that the role of the solvents is a critical factor in directing the assembly while retaining the 4-connecting Co(NCS) 2 [21]. We are currently investigating further the effects of solvent on crystal growth in the reactions of Co(NCS) 2 with ligands structurally related to 3-9.
FT-IR spectra were recorded on a PerkinElmer UATR Two instrument.

Crystallography
Single crystal data were collected on a STOE StadiVari Eulerian 4-circle diffractometer (CuKα radiation) equipped with a Dectris Eiger2 1M detector, or using a STOE StadiVari diffractometer equipped with a Pilatus300K detector and with a Metaljet D2 source (GaKα radiation) with data processing using STOE software (X-Area 1.90, STOE, 2020). Structures were solved using Superflip [31,32] and Olex2 [33]. The model was refined with ShelXL v. 2018/3 [34]. All H atoms were included at geometrically calculated positions and refined using a riding model with U iso = 1.2 of the parent atom. Structure analysis and structural diagrams used CSD Mercury 2022.1.0 [30].
In  2nMeOH. In each case, the electron density removed was accounted for in terms of added solvent molecules, and these were added to the formulae and all appropriate numbers.
PXRD data were collected at 295 K in transmission mode using a Stoe Stadi P diffractometer equipped with CuKα1 radiation (Ge(111) monochromator and a DECTRIS MYTHEN 1K detector). Whole-pattern profile matching analysis [35][36][37] of the diffraction patterns was performed using the package FULLPROF SUITE (v. January 2021) [37,38] applying a previously determined instrument resolution function based on a NIST640d standard. The structural models were derived from the single crystal X-ray diffraction data. Refined parameters in Rietveld were scale factor, zero shift, lattice parameters, background points, and peak shapes as a Thompson-Cox-Hastings pseudo-Voigt function. Preferred orientations as a March-Dollase multi-axial phenomenological model were incorporated into the analysis.
Thermogravimetric analysis was carried out under nitrogen on a TGA5500 instrument coupled to a Discovery II MS, Cirrus 3 mass spectrometer. A Barchart scanning method in the mass range 10-125 or 12-160 was used, and the temperature of the TGA instrument was initially stabilized at 30 • C. The samples were heated to 210 • C, and this was maintained for 30 min.

Conclusions
We have reported the single-crystal structures of [Co(NCS) 2  2nMeOH, in which the ligands 3-8 are bis(3,2 :6 ,3 -tpy) ligands with n-alkyloxy substituents ranging from n-propyl to n-octyl. Crystals were grown by layering a MeOH solution of Co(NCS) 2 over a 1,2-Cl 2 C 6 H 4 solution of 3-8. For each compound, the assembly of a (6 5 .8) cds net was observed. Despite the increasing steric demands of the ligands, the network remains little perturbed, and the n-alkyloxy chains (all in extended) are accommodated in cavities in the lattice with a concomitant decrease in the solvent-accessible void space within the net. The assembly of the cds net rather than other possible nets is critically dependent upon the choice of solvents for the crystal growth. We are currently exploring the effects of using different solvent systems and will report on these findings in the near future.