Crystal structure and Hirshfeld surface analysis of dichlorido(methanol-κO)bis(2-methylpyridine-κN)copper(II)

In the title complex, the CuII is in a tetragonal–pyramidal environment. The crystal structure features O—H⋯Cl and C—H⋯Cl interactions.

Both organic (from simple molecules to peptides and proteins) and inorganic complexes have been known for more than a century and are central to modern chemistry because of their fascinating, aesthetic architectures and multiple applications (Gan et al., 2011;Gellman, 1998;Thorat et al., 2013;Vijayadas et al., 2013;Ziach et al., 2018). Recently, coordination compounds have been reported that find applications in fields such as catalysis, gas storage, separation technology and molecular sensing (Mueller et al., 2006;Wan et al., 2006;Fé rey et al., 2003;James, 2003;Eddaoudi et al., 2002;Ruben et al., 2005, Kitagawa et al., 2004. There are many reports of coordination complexes where solvent molecules are located in the voids of the crystal structure. However, reports describing the replacement of coordinated solvent molecules with other molecules are relatively scarce. As part of ongoing work in our laboratory, employing pyridine ligands in the preparation of various coordination networks (PrakashaReddy & Pedireddi, 2007), we have extended our work to the synthesis of other coordination networks. A literature survey revealed that coordination complex aquadichlorobis(2-methylpyridine)copper(II) had been reported (Marsh et al., 1982). Our interest was to see whether we could replace the coordinated water molecule in the complex with other solvent molecules such as methanol or ethanol via single-crystal-to-single-crystal transition (SCSCT) to investigate the structural changes. Although we could not succeed in SCSCT of the complex, we were successful in synthesizing the methanol-coordinated copper complex incorporating 2-methylpyridine as reported herein. ISSN 2056-9890

Structural commentary
The title complex crystallizes in the monoclinic space group C2/c with one complex molecule per asymmetric unit. Two nitrogen atoms of 2-methylpyridine and two chloride ligands, which are trans to each other, form a rectangle around the copper atom, and its coordination is accomplished by the methanol oxygen atom, thus giving a tetragonal pyramid with the oxygen atom in the apical position (Fig. 1). The copper atom deviates by 0.161 (1) Å from the basal plane, and the angles around the copper atom are close to 90 and 180 . A plausible reason why the formation of a dimeric unit, as observed in [Cu(2-pic) 2 Cl 2 ] (Marsh et al., 1982), was precluded might be the presence of the coordinated methanol molecule on one side of the coordination rectangle and the methyl groups on the other side. The methylpyridine rings form angles of 83.96 (8) and 85.70 (8) with respect to the basal plane of the coordination polyhedron, thereby plausibly blocking the sixth coordination position at the copper atom. The Cu-O bond distance of 2.353 (2) Å is relatively short for an apical atom in typical copper(II) tetragonal-pyramidal structure, whereas the Cu-N bond lengths [Cu1-N1= 2.031 (2) Å , Cu1-N2 = 2.017 (2) Å ] agree well with those reported for related structures (Wang et al., 2006;Gong et al., 2009;Hu & Zhang, 2010;Li, 2011;Sun et al., 2013;Sanram et al., 2016).

Supramolecular features and Hirshfeld surface analysis
Complex molecules related by the twofold rotation axis are connected by pairs of O-HÁ Á ÁCl interactions (Table 1) involving the apical methanol ligand of one complex and a chloride ligand of the other, thus forming dimers (Fig. 2). The OÁ Á ÁCl and HÁ Á ÁCl distances and associated O-HÁ Á ÁCl angle lie within the ranges observed for other O-HÁ Á ÁCl interactions reported in the literature (Veal et al., 1972;Taylor,  The molecular structure of the title compound, showing the atom labelling and displacement ellipsoids drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; y; Àz þ 1 2 ; (ii) x À 1 2 ; y þ 1 2 ; z.

Figure 2
The O-HÁ Á ÁCl interactions between two molecules in the crystal of the title compound. The molecules are related by the symmetry operation Àx + 1, y, Àz + 1 2 .

Figure 3
A general view of the crystal packing of the title compound along the baxis direction with intermolecular contacts shown as dashed lines.
2016; Ristić et al., 2020;Estes et al., 1976). These dimers are further connected through C-HÁ Á ÁCl interactions, generating layers parallel to (001) (Fig. 3, Table 1). A Hirshfeld surface analysis was performed and twodimensional fingerprint plots were prepared using Crystal Explorer17 (Turner et al., 2017) to further investigate the intermolecular interactions in the title structure. The Hirshfeld surface mapped over d norm with corresponding colours representing intermolecular interactions is shown in Fig. 4.
The red spots on the surface correspond to the O-HÁ Á ÁCl, C-HÁ Á ÁCl and C-HÁ Á ÁO interactions (Table 1). The twodimensional fingerprint plots (McKinnon et al., 2007) are shown in Fig. 5. Weak van der Waals HÁ Á ÁH contacts make the largest contribution (53.1%) to the Hirshfeld surface. The twodimensional fingerprint plot shows two spikes that correspond to HÁ Á ÁCl/ClÁ Á ÁH (25.2%) interactions, which highlight the hydrogen bonds between adjacent molecules. The CÁ Á ÁH/ HÁ Á ÁC (15.5%) interactions also appear as two spikes. These interactions play a crucial role in the overall cohesion of the crystal packing.

Synthesis and crystallization
2-Methylpyridine and anhydrous copper(II) chloride were obtained from Aldrich, and HPLC grade methanol was used for reaction. Anhydrous copper(II) chloride (0.675 g, 0.005 mol) was dissolved in 15 ml of methanol. To this solution, 2-methylpyridine (0.93 g, 0.01 mol) dissolved in 15 mL of methanol was added. The resulting mixture was stirred for ca 40 min. at room temperature and filtered to remove the greenish precipitate. The blue filtrate was then allowed to stand at room temperature for a few hours, before being filtered and left at room temperature for crystallization. A mixture of dark-blue crystals of different sizes was obtained after 24 h.     program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Dichlorido(methanol-κO)bis(2-methylpyridine-κN)copper(II)
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.