Crystal structure, Hirshfeld surface analysis and geometry optimization of 2-hydroxyimino-N-[1-(pyrazin-2-yl)ethylidene]propanohydrazide

The title compound, 2-hydroxyimino-N-[1-(2-pyrazinyl)ethylidene]propanehydrazide, is a ligand able to form polynuclear metal complexes. The molecule is not planar due to a twist between the oxime and amide groups. In the crystal, molecules are linked by O—H⋯O hydrogen bonds into supramolecular chains.


Chemical context
The combination in one molecule of two donor sets of a different nature, such as oxime and hydrazide, might be the key to creating new asymmetric polynucleative ligands suitable for the formation of polynuclear complexes. In recent decades, a number of ligands based on 2-hydroxyiminopropanehydrazide have been obtained. It was shown that such a type of ligand reveals a strong tendency for the formation of polynuclear complexes (Anwar et al., 2011(Anwar et al., , 2012Fritsky et al., 2006;Jin et al., 2022).
The title compound, 2-hydroxyimino-N-[1-(pyrazin-2yl)ethylidene]propanohydrazide (1), was first described in the work of Feng and co-workers (Feng et al., 2018). It acts as a ligand in three new polynuclear heterometal porous coordination polymers, which have displayed high CO 2 adsorption uptake and high adsorption selectivity of CO 2 over N 2 and CH 4 . The present work is devoted to the synthesis, crystal structure, spectroscopic characterization, Hirshfeld surface analysis and quantum mechanical geometry optimization of 1.

Figure 3
The Hirshfeld surface of the title molecule 1 mapped over d norm , showing the close contacts.

Figure 1
The molecular structure of the title compound 1 with displacement ellipsoids shown at the 50% probability level.
Explorer17 (Turner et al., 2017). The Hirshfeld surfaces of the complex anions are colour-mapped with the normalized contact distance (d norm ) from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii). The Hirshfeld surface of the title compound mapped over d norm , in the colour range À0.6441 to 1.3084 a.u. is shown in Fig. 3. According to the Hirshfeld surface, O2-H2Á Á ÁO1 and C4-H4AÁ Á ÁN2 are the most noticeable intermolecular interactions. In addition, a C2-H2AÁ Á ÁO2 weak intermolecular interaction is observed. A fingerprint plot delineated into specific interatomic contacts contains information related to specific intermolecular interactions. The blue colour refers to the frequency of occurrence of the (d i , d e ) pair with the full fingerprint plot outlined in grey. Fig. 4 shows the two-dimensional fingerprint plots of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. The most significant contribution to the Hirshfeld surface is from HÁ Á ÁH (41.9%) contacts. In addition, NÁ Á ÁH/HÁ Á ÁN (20.5%) and OÁ Á ÁH/ HÁ Á ÁO (15.4%) are highly significant contributions to the total Hirshfeld surface. The OÁ Á ÁH/HÁ Á ÁO fingerprint plot ( Fig. 4d) reveals two sharp spikes along 1.9 Å < d i + d e < 2.4 Å , which are associated with the O2-H2Á Á ÁO1 hydrogen bond.

Geometry optimization
The DFT quantum-chemical calculations were performed at the B3LYP/6-311 G(d,p) level (Becke, 1993) as implemented in PSI4 software package (Parrish et al., 2017). The GFN2-xTB (Bannwarth et al., 2019) calculations were applied with xtb 6.4 package (Grimme, 2019). The structure optimization of the title compound was performed starting from the X-ray geometry and the resulting geometric values were compared with experimental values (Table 2, Fig. 5). The r.m.s. deviations are 0.380 and 0.362 Å for DFT and GFN2-xTB, respectively.
The calculated geometric parameters are in good agreement with experimental values. It is important to note that the accuracy of the semi-empirical GFN2-xTB method is close to that of the DFT calculations, even though GFN2-xTB calculations are significantly computationally 'cheaper' ($2Á10 3 times faster for the calculations described here).
The most significant difference between the calculated and X-ray geometries is the absence of a twist deformation between the oxime and the amide groups in the case of QM calculated geometries. This might be additional evidence that the twist distortion of the molecule is due to effects of the crystal packing. The largest differences between the X-ray and calculated bond lengths are observed for the hydrazide moiety: N3-N4 is slightly longer (0.019 and 0.034 Å for DFT and GFN2-xTB, respectively) and C7-N4 is shorter (0.050 and 0.036 Å for DFT and GFN2-xTB, respectively) than calculated. Such calculation errors are probably typical for 902 Plutenko et al.

Figure 5
Overlay between the molecule obtained from experimental (orange) and DFT optimization (blue).
hydrazide derivatives at this level of theory (Anitha et al., 2019;Malla et al., 2022). The HOMO-LUMO gap calculated by DFT method is 0.159 a.u. and the frontier molecular orbital energies, E HOMO and E LUMO are À0.23063 and À0.07178 a.u., respectively.

Synthesis and crystallization
The title compound was prepared according to a slightly modified procedure (Feng et al., 2018). A solution of 2-(hydroxyimino)propanehydrazide (0.702 g, 5 mmol) in methanol (50 ml) was treated with 2-acetylpyrazine (0.732 g, 5 mmol) and the mixture was heated under reflux for 1.5 h. After that, the solvent was evaporated under vacuum and the product was recrystallized from methanol. Yield 1.141 g (86%

2-hydroxyimino-N-[1-(pyrazin-2-yl)ethylidene]propanohydrazide
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.