catena-Poly[[aqua(imidazole)cadmium(II)]-μ3-benzene-1,3-dicarboxylato]

In the title compound, [Cd(C8H4O4)(C3H4N2)(H2O)]n, the CdII ion is seven-coordinated by five O atoms from three crystallographically independent benzene-1,3-carboxylate ligands, one N atom from the imidazole ligand and one coordinated water molecule. Neighboring CdII ions are bridged by the benzene-1,3-dicarboxylate ligands, forming a zigzag polymeric chain structure. These chains are further extended into a three-dimensional supramolecular structure through O—H⋯O and N—H⋯O hydrogen bonds.

In the title compound, [Cd(C 8 H 4 O 4 )(C 3 H 4 N 2 )(H 2 O)] n , the Cd II ion is seven-coordinated by five O atoms from three crystallographically independent benzene-1,3-carboxylate ligands, one N atom from the imidazole ligand and one coordinated water molecule. Neighboring Cd II ions are bridged by the benzene-1,3-dicarboxylate ligands, forming a zigzag polymeric chain structure. These chains are further extended into a three-dimensional supramolecular structure through O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds.

Comment
In recent years, considerable effort was paied in the study of metal-organic hybrid materials with the extended supermolecular framework structures, owing to their intriguing network topologies and potential application in adsorption, molecular recognition, catalysis and maganetism (Yaghi et al., 1998 ). Currently, carboxylic acids have been widely used as polydentate and bridging ligands since they can bind metal ions in diverse modes and play an important role in adjusting verious topologies structures. A number of promising supramolecular complexes have been designed and constructed by using carboxylic acids as favorable conditions. (Ma et al., 2008;Wang et al., 2008). In this paper, we report the synthesis and structural characterzation of the title compound in which the isophthalic acid ligand displayed its good coordination ability and diverse coordination modes.
The Cd II ion is six-coordinated by four O atoms from three crystallographically independent benzene-1,3-dicarboxylate ligands and one N atom from the chelating imidazole ligand and one coordinated water molecule ( Fig. 1 & Table 1). The neighboring Cd i ion is bridged by the benzene-1, 3-dicarboxylate ligands to form a one-dimensional chain structure. In the crystal structure, the adjacent chains are linked via O-H···O and N-H···O hydrogen bonds ( Fig. 2 & Table 2) resulting in the formation of a three dimensional supramolecular structure.

Experimental
A 10 ml aqueous solution of imidazole (0.014 g, 0.20 mmol) and isophthalic acid (0.034 g,0.020 mmol) was slowly added into cadmium nitrate (0.062 g, 0.20 mmol) solution in methanol (10 ml), and the mixed solution was stirred for 20 min and then was heated in a 30 ml Teflon-line autoclave under autogeneous pressure at 423 K for 3 d. After cooling to room temperature, colorless block crystals were obtained. (yield 38%).

Refinement
H atoms bound to H 2 O and NH atoms were located in a difference map and refined freely. Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms. [Symmetry codes:

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 > 2sigma(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.