trans-Dichloridobis(secnidazole-κN 3)copper(II)

The crystal structure of the title complex is stabilized by intermolecular O—H⋯Cl hydrogen bonds, forming (18) ring motifs.

The use of acetic acid (HOAc) in a reaction between CuCl 2 •2H 2 O and secnidazole, an active pharmaceutical ingredient useful in the treatment against a variety of anaerobic Gram-positive and Gram-negative bacteria, affords the title complex, [CuCl 2 (C 7 H 11 N 3 O 3 ) 2 ].This compound was previously synthesized using ethanol as solvent, although its crystal structure was not reported [Betanzos-Lara et al. (2013).Inorg.Chim.Acta, 397, 94-100].In the molecular complex, the Cu 2+ cation is situated at an inversion centre and displays a squareplanar coordination environment.There is a hydrogen-bonded framework based on intermolecular O-H� � �Cl interactions, characterized by H� � �Cl separations of 2.28 (4) A ˚and O-H� � �Cl angles of 175 (3) � .The resulting supramolecular network is based on R 2 2 (18) ring motifs, forming chains in the [010] direction.

Structure description
Secnidazole [C 7 H 11 N 3 O 3 , IUPAC name: 1-(2-methyl-5-nitro-1H-imidazol-1-yl)propan-2ol, abbreviated secnim] is an active pharmaceutical ingredient used in the treatment against a variety of anaerobic Gram-positive and Gram-negative bacteria (Gillis & Wiseman, 1996).Some coordination complexes including secnidazole as a ligand were synthesized with late transition metals, Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ (Betanzos-Lara et al., 2013).Following the ideas of that group, the aim of this study is to obtain new complexes, to evaluate the synergistic effect of coordination of secnidazole to copper(II) on the antimicrobial activity.
In the literature, only one crystal structure of a secnidazole metallic complex has been reported (CSD refcode KICFUZ; Betanzos-Lara et al., 2013).The complex consists of a dinuclear cluster of Cu 2+ surrounded by four acetate anions OAc À and two secnidazole molecules bonded in terminal positions, to give [Cu 2 (secnim) 2 (� 2 -OAc) 4 ].The same authors synthesized [Cu(secnim) 2 Cl 2 ], although they did not determine its crystal structure.We have now obtained the same mononuclear complex using a simple synthetic route (see Experimental), and determined its molecular and crystal structure.
The mononuclear Cu 2+ ion is surrounded by two secnim molecules trans-coordinated through the imidazolic nitrogen atom N3, and two chloride ions, giving a distorted squareplane geometry for Cu II , with Cu1-N3 and Cu1-Cl1 bond lengths being 1.9953 (19) A ˚and 2.2586 (6) A ˚, respectively.The metal is located at an inversion centre in space group P1, and the asymmetric unit contains half a molecule (Fig. 1).A molecular overlay shows that the global conformation of the secnim free ligand (Novoa de Armas et al., 1997) is not altered by coordination to the central metal (Fig. 2).The most significant modification is related to the free rotation of the NO 2 group bonded to C5 in the ligand.The dihedral angle between the nitro group and the mean plane of the imidazole ring is 1.0 � in the non-coordinating ligand, while this angle is 15.2 (4) � in the complex.Such a rotation could be a consequence of a steric hindrance between the nitro group and the propan-2-ol lateral chain in a neighbouring molecule in the crystal (Table 1, entry 2).
The orientation of the hydroxy group promotes the formation of intermolecular hydrogen bonds and acts as a donor to the chloride ion, which acts as an acceptor (Table 1, entry 1).The crystal structure features centrosymmetric R 2 2 (18) ring motifs formed by the interaction between the noncoordinating hydroxy group and the chloride ion of a symmetry-related complex.A periodic framework is created, based on chains running in the [010] direction (Fig. 3).These chains are parallel in the crystal, and interact poorly, through weak C-H� � �O contacts involving the hydroxy and nitro groups as acceptors (Table 1, entries 2 and 3).

Synthesis and crystallization
Two ethanolic solutions of secnim (185 mg, 1 mmol in 15 ml) and CuCl 2 •2H 2 O (170 mg, 1 mmol, in 15 ml) were prepared at ambient conditions.Acetic acid (5 ml) was added to the CuCl 2 •2H 2 O solution.The solutions were combined under stirring for 1 h at 333 K.The resulting solution was then filtered and allowed to evaporate at 298 K over 2 days, affording blue single crystals suitable for X-ray crystallography.

Figure 2
An overlay calculated with Mercury (Macrae et al., 2020), comparing the shape of secnidazole as free ligand (red molecule; Novoa de Armas et al., 1997) and in the title compound (green molecule).The overlay was computed using the five atoms belonging to the imidazole heterocycle.Note the small rotation of ca 14 � for the nitro group.

Figure 3
Part of the supramolecular framework based on intermolecular O-H� � �Cl hydrogen bonds (dashed purple lines) corresponding to the first entry in Table 1, as viewed down [100].

Special details
Refinement.Methine, methylene and methyl H atoms were refined using a riding model and calculated displacement parameters, while hydroxy H atom (H3) was refined with free coordinates and isotropic displacement parameter.

Table 2
Experimental details.