Aquabis(1H-benzimidazole-2-carboxylato-κ2 O,N 3)zinc(II)

In the title compound, [Zn(C8H5N2O2)2(H2O)], the ZnII ion is coordinated in each case by a carboxylate O atom and an imidazole N atom from two different benzimidazole-2-carboxylate (BIC) ligands and one water O atom in a trigonal-bipyramidal geometry. In the complex molecule, the two benzimidazole planes are twisted, making a dihedral angle of 55.93 (11)°. The three-dimensional framework is organized by intermolecular N—H⋯O hydrogen bonding and O—H⋯O interactions and π–π interactions between adjacent benzimidazole rings [centroid–centroid distance = 3.586 (3) Å].

In the title compound, [Zn(C 8 H 5 N 2 O 2 ) 2 (H 2 O)], the Zn II ion is coordinated in each case by a carboxylate O atom and an imidazole N atom from two different benzimidazole-2carboxylate (BIC) ligands and one water O atom in a trigonal-bipyramidal geometry. In the complex molecule, the two benzimidazole planes are twisted, making a dihedral angle of 55.93 (11) . The three-dimensional framework is organized by intermolecular N-HÁ Á ÁO hydrogen bonding and O-HÁ Á ÁO interactions andinteractions between adjacent benzimidazole rings [centroid-centroid distance = 3.586 (3) Å ].
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KP2256). metal-organic compounds m610 Di et al. al., 2005), those related to the benzimidazole-2-carboxylic acid(BICA) are reported rearly. Benzimidazole analogues are known to exhibit a wide variety of pharmacological properties; benzimidazole is an important pharmacophore and privileged structure in medicinal chemistry encompassing a diverse range of biological activities (Shingalapur et al., 2009). In the viewpoint of constructing new functional complex, we prepared aqua(1H-benzo[d]imidazole-2-carboxylato-κ 2 O:N)-zinc (II) with the formula [Zn(C 8 H 5 N 2 O 2 ) 2 (H 2 O)] (I) and report its structure.
In (I) Zn II coordination sphere is completed by carboxylato O atom and imidazole N atom from two different ligand molecules and one O atom from water ( Fig. 1). The two BICA molecules are deprotonated to make the molecule neutral, then the BICligand behaves as a chelating unit that binds through the imidazole N atom and carboxylato O atom, giving a five-membered chelate ring. The structural index τ (Addison et al. 1984) which represents the relative amount of trigonality of the five-coordination geometry as τ = 0 for a square pyramid and τ = 1 for a trigonal bipyramida in (I) is 0.791, therefore, the coordination geometry around Zn II seems to be classified as a trigonal bipyramid rather than a square pyramid; N3, O5, and N1 atoms form the equatorial trigonal plane indicated by the angle of O5-Zn-N1 and O5-Zn1-N3 being 116.39 (12)° and 115.42 (12) °, respectively. The axial position occupy O2 and O4 atoms; O4-Zn-O2 is the only combination with bonding angle close to 180 degrees. Therefore, the five-coordination geometry around Zn is classified as a distorted trigonal bipyramid with ZnN 2 O 3 core. Compared with the other analogous zinc complexes, the bond distance of Zn II and carboxylato O in (I) is in the normal range from 2.1445 (12) Å to 2.201 (3) Å (Table 1) (Zhong et al., 2006).
The benzimidazole moiety in each ligand is nearly coplanar with the mean deviation from plane by 0.0059 Å and 0.0042 Å for ring C1-C7/N1/N2 and C10-C16/N3/N4, respectively. Around Zn II two five-chelate rings are formed with slightly different conformations. The ring Zn1/N1/C7/C8/O2, adopts an envelope conformation with the deviation of Zn atom from the mean plane by 0.0686 (16) Å whereas the related ring Zn1/N3/C10/C9/O4 seems to be planar with the corresponding distance 0.0056 (14) Å. The dihedral angle of two benzimidazole groups around Zn II is about 55.93 (11) ° leading to the intersection mode in the stack (Fig.2). In the ab plane, the whole zig-zag motif is bulit up, together with the π-π interactions between the adjacent benzimidazole planes along the axis a. The pairs of the two benzimidazole rings are oriented almost parallel and overlap face to face with the Cg···Cg distances of 3.586 (3) Å (where Cg is the center of gravity of the benzi-supplementary materials sup-2 midazole ring) for the centroid···centroid separations of rings N1 / N2 / C1-C7 and N1 / N2 / C1-C7(symmetry code: 1-x, y, 3/2-z). The three-dimensional framework is defined by intermolecular hydrogen bonds involving water molecules, the uncoordinated imidazole N atoms, and carboxylate O atoms(N-H···O and O-H···O, Table 2 and Fig. 2).
Experimental 1H-benzo[d]imidazole-2-carboxylic acid(20 mg, 0.12 mmol) and zinc chloride dihydrate (10 mg, 0.06 mmol) were separately dissolved in 5 ml methanol. The solutions were mixed and stirred magnetically for 2 h. Colourless single crystals were isolated from the solution at room temperature over several days.

Refinement
At first, all H atoms were located from the difference Fourier maps, and then were treated as riding [C-H = 0.93 Å ; U iso (H) = 1.2 times U eq ; imidazole N-H = 0.86 Å and O-H = 0.85 Å; U iso (H) = 1.5 times U eq ]. The weighting schemes were optimized . Fig. 1. ORTEP drawing of (I) with the atomic numbering scheme. Ellipsoids for non-H atoms corresponding to 50 % probability.

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq