Synthesis, crystal structure and Hirshfeld surface analysis of a copper(II) complex involving 3-methylbenzoate and 2,2′-bipyridine ligands

A new copper(II) complex with 3-methylbenzoate and 2,2′-bipyridine synthesized displays chains of hydrogen-bonded complex units along the b axis. Hirshfeld surface analysis indicates that H⋯H and H⋯C/C⋯H contacts are the most important interactions.


Chemical context
The coordination chemistry of mixed-ligand copper(II) complexes continues to be of interest.Copper is an important part of various metalloenzymes.It takes part in many metabolic processes such as iron metabolism, mitochondrial oxidative phosphorylation and catecholamine production (Chen et al., 2020;De Freitas et al., 2003).Mixed-ligand copper(II) carboxylates containing nitrogen donor ligands have been reported to display a variety of pharmacological and superoxide dismutase activities.For example, the bis-(acetato)bis(imidazole)copper(II) complex exhibits antitumor activity (Tamura et al., 1987) and copper(II) salicylate with imidazoles have dismutase activities (Abuhijleh, 2010).Incorporating nitrogen donor ligands in metal complexes has resulted in enhancement of the biological activity of these complexes (Patel et al., 2012).It has been reported that the steric effect of a substituent on the phenyl group of carboxylate ligands in metal complexes affects the coordination number of the metal, the geometry of the complex and the coordination mode of the ligand (Saini et al., 2015).In our previous contribution, the Cu II complex with 3-mb and N,N,N, N-tetramethylethylenediamine (tmeda),  2 (tmeda)-(H 2 O) 2 ], was prepared and characterized by single-crystal X-ray diffraction.The complex was octahedral with 3-mb acting as monodentate (Kansız et al., 2021).In view of the above information, a new Cu II carboxylate containing 2,2 0bipyridine was synthesized, characterized by X-ray crystallographic analysis and studied by Hirshfeld surface analysis.

Supramolecular features
In the crystal, hydrogen bonding between H atoms of the coordinated water molecule and the O atoms of the coordinated 3-mb (O5-H5B� � �O4) leads to the formation of a linear chain in the b-axis direction (Fig. 2 and Table 1).The chains interdigitate with other chains related by a screw-axis, connected via C-H� � �O interactions between O atoms of the 3-mb ligand and H atoms of the bipy ligand (Table 1), further consolidating the crystal.The occupancy of the solvent water (H6A-O6-H6B) refined to 0.68, which seems to be due to water escaping the crystal through the channels that run along the b-axis direction.

Hirshfeld surface analysis
CrystalExplorer (Turner et al., 2017) was used for Hirshfeld surface analysis and to generate the fingerprint plots.The purpose of using Hirshfeld surfaces, mapped onto d norm , is to provide additional insight into intermolecular interactions.
Close contacts shorter than van der Waals radii are shown as red spots on the surface.The closest contacts are responsible for directional supramolecular interactions.The blue areas in the surface map represent weak contacts that are longer than the sum of the van der Waals radii.The Hirshfeld surface mapped onto d norm , is presented in Fig. 3.It displays several red spots due to O-H� � �O and C-H� � �O contacts.The intense spot near the coordinated water molecule in the complex is assigned to the O5-H5� � �O hydrogen bond, as confirmed by the X-ray analysis (Table 1).Fingerprint plots for the contacts are shown in Fig. 4. The contributions of the H� � �H (Fig. 4b), H� � �C/C� � �H (Fig. 4c) and H� � �O/O� � �H (Fig. 4d) contacts are 56.8,21.7 and 13.7%, respectively.

Synthesis and crystallization
3-Methylbenzoic acid (4 mmol, 0.54 g) and sodium hydroxide (4 mmol, 0.16 g) in water (20 ml) were added to a solution of Cu(NO 3 ) 2 •3H 2 O (2 mmol, 0.48 g) in water (20 ml) under stirring.A solution of 2,2 0 -bipyridine (2 mmol, 0.3 g) in EtOH (25 ml) was added and the color changed from greenish blue to blue.The precipitate was filtered off, washed with water and dried.Blue single crystals of the title complex suitable for X-ray diffraction studies were obtained after evaporation of an ethanol solution after several days.
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Figure 3
Hirshfeld surface map for the title complex.

Figure 4
Fingerprint plot of the title compound showing all interactions and delineated into the most important intermolecular contacts.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.One of the 3-methylbenzoates (O3/O4/C9-C16) is disordered over two positions related by a 180 � rotation.The occupancies of the two components refined to 0.664 (4):0.336(4).The occupancy of the water molecule H6A-O6-H6B refined to 0.680 (10).The coordinates of the ordered water atom were refined with U iso (H) = 1.5U eq (O).
All other H atoms were positioned geometrically and refined as riding with U iso (H) = 1.2-1.5Ueq (parent atom).

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.

Figure 1
Figure 1Molecular structure of complex 1 with ellipsoids drawn at the 50% probability level.Only the major component of disorder is shown.

Figure 2
Figure 2 Partial view of the packing arrangement in compound 1 showing O-H� � �O interactions along the b-axis direction.

Table 2
Experimental details.