Poly[[(μ-1H-benzimidazole-5,6-dicarboxylato)zinc(II)] monohydrate]

The three-dimensional polymeric title compound, {[Zn(C9H4N2O4)]·H2O}n, contains one crystallographically independent ZnII atom, one fully deprotonated 1H-benzimidazole-5,6-dicarboxylate (bdc) ligand and one uncoordinated water molecule. The ZnII atom is four-coordinated by three O atoms and one N atom from the bdc ligands, giving a distorted tetrahedral coordination geometry. The uncoordinated water molecule is bound to the main structure through a strong bdc–water N—H⋯O hydrogen bond, and two much weaker water–bdc O—H⋯O interactions.

The three-dimensional polymeric title compound, {[Zn (C 9 H 4 N 2 O 4 )]ÁH 2 O} n , contains one crystallographically independent Zn II atom, one fully deprotonated 1H-benzimidazole-5,6-dicarboxylate (bdc) ligand and one uncoordinated water molecule. The Zn II atom is four-coordinated by three O atoms and one N atom from the bdc ligands, giving a distorted tetrahedral coordination geometry. The uncoordinated water molecule is bound to the main structure through a strong bdcwater N-HÁ Á ÁO hydrogen bond, and two much weaker water-bdc O-HÁ Á ÁO interactions.
Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97. Zhao-yang Li, Jing-wei Dai and Shan-tang Yue S1. Comment N-Heterocyclic carboxylic acids have atracted attention not only because their versatile coordination modes but also owing to their forming high-dimensional polymers through H-bonding interactions. 1H-benzimidazole-5,6-dicarboxylic acid (bdc), having six coordination points, is a good candidate for the generation of three-dimensional coordination polymers. However, up to now the complexes based on the bdc ligand are rare (Lo et al., 2007;Gao et al., 2008;Wei et al., 2008;Yao et al., 2008). Here we report the first three-dimensional Zn coordination polymer connected by bdc ligands, [Zn(C 9 As is shown in Figure 1, the asymmetric unit consists of one Zn 2+ cation, a fully deprotonated bdc 2ligand, and a free water moelcule. The cation has a tetrahedral coordination environment, and is surrounded by three oxygen and one nitrogen atoms from the bdc ligands. A packing diagram showing the 3D structure coming out from the tetradentate character of the bdc ligand is shown in Figure 2. To the best of our knowledge, the title compound is the first 3D transition metal coordination polymer based on the 1H-benzimidazole-5,6-dicarboxylic acid ligand.

S2. Experimental
A mixture of bdc (0.0415 g, 0.20 mmol), Zn(NO 3 ) 2 .6H 2 O (0.0594 g, 0.20 mmol) and water (10 ml) was heated up to 430 K for 72 h in a 23 ml Teflon-lined stainless-steel autoclave and then cooled down to room temperature in a 278 K/hour rate. Colourless prismatic crystals were collected and dried in air.

Figure 2
The packing diagram of the title compound, with H atoms omitted for clarity. Hydrogen bonds are shown as dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.