Crystal structure of bis[2-(1H-benzimidazol-2-yl-κN 3)aniline-κN]bis(nitrato-κO)cadmium(II)

The synthesis and crystal structure of the title 2-(1H-benzimidazol-2-yl)aniline CdII complex is reported in which the CdII atom lies on a twofold rotation axis and is coordinated by four N atoms, provided by two bidentate 2-(1H-benzimidazol-2-yl)aniline ligands, and two nitrato O atoms, forming a distorted octahedral geometry.


Chemical context
Azole and benzazole derivatives are well-known nitrogencontaining heterocyclic compounds, and are of great interest because of their broad spectrum of biological activity (Esparza-Ruiz et al., 2011;Hock et al., 2013). Imidazole is an azapyrrole in which the nitrogen atoms are separated by one carbon atom. Benzimidazole, a fused heterocycle with benzene and imidazole, is associated with a wide array of pharmacological activities (Akhtar et al., 2017), and benzimidazole derivatives exhibit a wide range of various biological activities. These include bactericidal (Carcanague et al., 2002) and fungicidal (Lezcano et al., 2002;Aghatabay et al., 2007) properties. Their metal complexes have been shown to display antitumor activity and are important biological molecules (Sá nchez-Guadarrama et al., 2009;Ramla et al., 2007;Wang et al., 2007). Recently, we reported on the synthesis and structural features of Zn (Kim & Kang, 2015a) and Ag (Kim & Kang, 2015b) complexes with benzimidazole derivatives. In this work, we have synthesized the title compound and characterized it by single crystal X-ray crystallography. ISSN 2056-9890

Supramolecular features
In the crystal, molecules are linked by a series of N-HÁ Á ÁO interactions. The nitrate group containing oxygen atom O21 forms both intra-and intermolecular hydrogen bonds. Molecules are arranged into a zigzag chain along the c-axis direction via an N-HÁ Á ÁO hydrogen bond (N17-H17BÁ Á ÁO20 ii ; symmetry code as in Table 1; Fig. 2). The other N-HÁ Á ÁO hydrogen bonds (N9-H9Á Á ÁO20 i and N9-H9Á Á ÁO21 i ; Table 1) link the molecules into a three-dimensional network (Fig. 3).

Figure 2
Partial packing diagram of the title compound, showing molecules linked by intermolecular N-HÁ Á ÁO hydrogen bonds (dashed lines), viewed along the a-axis direction.

Synthesis and crystallization
Chemicals were obtained commercially in reagent grade and used as received. Solvents were dried using standard procedures described in the literature. To a stirred solution of Cd(NO 3 )Á4H 2 O (0.154 g, 0.5 mmol) in ethanol (20 ml) was added a solution of 2-(1H-benzimidazol-2-yl)aniline (0.209 g, 1.0 mmol) in ethanol (10 ml) at 333 K. After 24 h of stirring, the title complex was obtained as a white powder. The powder was filtered off and washed with ethanol. Colourless crystals of the title complex were obtained by slow evaporation of the methanol solvent at room temperature within two weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms of the NH and NH 2 groups were located in a difference-Fourier map and refined freely [refined distances: Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å , and with U iso (H) = 1.2U eq (C).

Funding information
This work was supported by the research fund of Chungnam National University.  Table 1).

Bis[2-(1H-benzimidazol-2-yl-κN 3 )aniline-κN]bis(nitrato-κO)cadmium(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.