Poly[[{μ2-3-[(1H-benzimidazol-1-yl)methyl]benzoato}cadmium(II)] 0.1-hydrate]

In the title polymeric compound, {[Cd(C15H11N2O2)2]·0.1H2O}n, the CdII atom is coordinated by four carboxylate O atoms and two benzimidazole N atoms from four benzimidazolylmethylbenzoate anions in a distorted octahedral geometry. Each anion bridges two Cd atoms through the terminal carboxylate group and an imidazole N atom, forming polymeric complex chains running along the b axis. The uncoordinated water molecule is equally disordered over two sites; occupancies were fixed as 0.5 for each disordered component. Weak intermolecular C—H⋯O hydrogen bonding is present in the crystal structure.

In the title polymeric compound, {[Cd(C 15 H 11 N 2 O 2 ) 2 ]Á-0.1H 2 O} n , the Cd II atom is coordinated by four carboxylate O atoms and two benzimidazole N atoms from four benzimidazolylmethylbenzoate anions in a distorted octahedral geometry. Each anion bridges two Cd atoms through the terminal carboxylate group and an imidazole N atom, forming polymeric complex chains running along the b axis. The uncoordinated water molecule is equally disordered over two sites; occupancies were fixed as 0.5 for each disordered component. Weak intermolecular C-HÁ Á ÁO hydrogen bonding is present in the crystal structure.

Related literature
For the use of benzimidazoles and benzimidazole derivatives in the construction of metal-organic frameworks, see: Li et al.

Comment
The rational design and synthesis of supramolecular complexes are of great interest not only because of their potential applications but also owing to their intriguing structures. Benzimidazole and benzimidazole-containing derivatives acted as one of the useful classes of organic building blocks to construct metal-organic frameworks (MOFs) (Li et al., 2010;Vijayan et al., 2006). Supramolecular complexes based on bent unsymmetric ligands containing benzimidazole and carboxylic acid groups have been less extensively studied, so these bent unsymmetric ligands offer great potential for creating novel frameworks. In the present work, the new bent organic ligand 3-[(1H-benzimidazole-1-yl)methyl]benzoic acid (HL) was employed in a self-assembly reaction with cadmium (II) iodide under hydrothermal conditions to create the novel supramolecular complex [Cd(C 15 H 11 N 2 O 2 ) 2 0.10(H 2 O)] n (I).
The compound structure of (I) is shown in Fig. 1. The asymmetric unit contains two L ligands, one Cd(II) and 0.10 water molecule. Compound (I) crystallizes with one unique six-coordinated Cd(II) center in a distorted octahedral {Cd N 2 O 4 } environment involving four O atoms from the carboxylate groups of two L ligands and two N atoms from benzimidazole of two other L ligands.
Neighboring Cd(II) ions are bound together by the carboxylate groups and terminal benzimidazole N donors of two L ligands to form a {Cd 2 L 2 } bimetallic ring in which the diagonal Cd···Cd separation is 9.907 (6) Å. The dihedral angle between benzimidazole ring and benzene ring is 87.618 (113)°. Small amounts of disordered water molecules are located in the bimetallic ring. Each Cd (II) center of the bimetallic ring is further bonded with two other bridging ligands resulting in a novel infinite one-dimensional extended chains structure in the crystallographic c axis. The Cd···Cd distance between adjacent bimetallic rings is 10.830 (2) Å, and the dihedral angle of benzimidazole ring and benzene ring of the ligand is 62.467 (82)°, it is worthy noted that the Cd···Cd distance is longer than that of in the bimetallic ring, which may be caused by the different features of the ligand. (Fig. 2).
In the solid state, when viewed down the crystallographic b axis, these one-dimensional chains are arranged in an ···AA··· fashion stack through interchain π-π interaction between two benzimidazole ring, the centroid-to-centroid distance of ca.

Experimental
A mixture of 3-[(1H-benzimidazole-1-yl)methyl)methyl]benzoic acid (25.2 mg, 0.10 mmol), CdI 2 (12.7 mg, 0.10 mmol) and deionized water (2 ml) was sealed in a 5 ml Teflon-lined stainless steel reactor and heated at 453 K for 40 h, and then cooled slowly to room temperature over a period of 50 h. Colorless single crystals were obtained from the reaction mixture.

Refinement
The lattice water is disordered over two sites, site occupancy factors for each components were refined and converged to 0.048 and 0.046, respectively; in the final cycles of refinement they were fixed as 0.5 for each. H atoms of water molecules were placed at calculated positions and refined with distance constraint of O-H = 0.85±0.001 Å, and U iso (H) = 1.5U eq (O).

Figures
Fig. 2. One-dimensional chain structure of (I), disordered water molecules located in the bimetallic ring.
Crystal data [Cd(C 15

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 )