Crystal structure of the mixed methanol and ethanol solvate of bis{3,4,5-trimethoxy-N′-[1-(pyridin-2-yl)ethylidene]benzohydrazidato}zinc(II)

The title compound belongs to the class of neutral pyridine aroylhydrazone complexes. In the crystal, π–π stacking leads to dimerization of the complex molecules, which, in turn, are connected by weak C⋯O and C⋯C interactions, thus giving rise to a supramolecular layered architecture.


Chemical context
Aroylhydrazones are an attractive class of ligands exhibiting coordination versatility toward a wide range of metals, particularly 3d transition metal ions (Bernhardt et al., 2006;Deng et al., 2016;Peng et al., 2017). Remarkable chelating ability together with synthetic accessibility led to the exploration of aroylhydrazones as potential metal-chelating drugs (Link et al., 2003;Bernhardt et al., 2007). Another field of application includes utilization of some aroylhydrazones as fluorescent probes and as metal-ion fluorescence chemosensors (Xiang et al., 2006;Wu et al., 2007).

Structural commentary
In the complex, the Zn II ion possesses a distorted octahedral N 4 O 2 coordination environment, which is generated by the two deprotonated ligands (Fig. 1). The average bond lengths [Zn-N = 2.145 (3) Å and Zn-O = 2.141 (2) Å ] are typical for such Zn II complexes (Jang et al., 2005;Barbazá n et al., 2007;Singh et al., 2015;Kane et al., 2016;Wang et al., 2019). The N2-Zn-N5 angle, formed by the ketimine N atoms of the two ligand molecules, is 164.81 (10) , showing the deviation of the coordination polyhedron from an ideal octahedral geometry. The average trigonal distortion parameters AE = AE 1 24 (60 À i )/24, where i is the angle generated by superposition of two opposite faces of the octahedron (Chang et al., 1990) and È = AE 1 12 (|' i À 90|)/12, where ' i is the deviation from 90 of the cis-N-Zn-N angles in the coordination sphere (Drew et al., 1995), are 18.38 and 11.65 , respectively, which correspond to a moderate distortion. The volume of the coordination polyhedron is 12.008 Å 3 .

Figure 1
The title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity.

Hirshfeld surface and 2D fingerprint plots
The Hirshfeld surface analysis and the associated twodimensional fingerprint plots were undertaken using Crystal-Explorer17.5 software (Turner et al., 2018), using standard surface resolution with the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.2580 (red) to 2.2951 (blue) a.u. The pale-red spots symbolize short contacts and negative d norm values on the surface correspond to the inter-actions described above. The overall two-dimensional fingerprint plot is illustrated in Fig. 3. The Hirshfeld surfaces mapped over d norm are shown for the HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, and CÁ Á ÁC contacts, and the two-dimensional fingerprint plots are presented in Fig. 4, associated with their relative contributions to the Hirshfeld surface. At 44.8%, the largest contribution to the overall crystal packing is from HÁ Á ÁH interactions, which are located in the middle region of the fingerprint plot. HÁ Á ÁC/CÁ Á ÁH contacts contribute to 22.2% to the Hirshfeld surface, resulting in two pairs of characteristic wings. The pair of tips of HÁ Á ÁO/OÁ Á ÁH contacts make a 18.7% contribution to the Hirshfeld surface. The contacts are represented by a pair of sharp spikes in the fingerprint plot. The CÁ Á ÁC contacts contribute only to 3.9% to the Hirshfeld surface. Two projections of d norm mapped on Hirshfeld surfaces, showing the intermolecular interactions within the molecule. Red areas represent contacts shorter than the sum of the van der Waals radii, while blue areas represent regions where contacts are larger than the sum of van der Waals radii, and white areas are zones close to the sum of van der Waals radii.

Synthesis and crystallization
The complex was obtained by condensation of 3,4,5-trimethoxybenzohydrazide (1 mmol) and acetyl pyridine (1.1 mmol) in a mixture of absolute MeOH and EtOH (1:1) overnight in the presence of two drops of glacial acetic acid. The ligand obtained in situ was subsequently reacted with solid ZnCl 2 Á6H 2 O (0.5 mmol) to give a colourless complex. A paleyellow solution was obtained after deprotonation with NEt 3 (1 mmol). The neutral complex was isolated by slow cooling the solution to ambient temperature and subsequently by filtering off the yellowish crystals. Elemental analysis calculated (%) for C 37

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions using idealized geometries, with C-H = 0.97 Å for mthyl goups and 0.93 Å for aromatic H atoms, and refined using a riding model with U iso (H) = 1.2-1.5U eq (C). None of the hydrogen atoms of the methanol or ethanol molecules could be located.

Funding information
Funding for this research was provided by: H2020 Marie Skłodowska-Curie Actions (grant No. 734322).