A novel two-dimensional cadmium(II) complex: poly[diaquatris(μ4-cyclohexane-1,4-dicarboxylato)bis[2-(pyridin-4-yl)-1H-benzimidazole]tricadmium(II).

The title compound, [Cd3(C8H10O4)3(C12H9N3)2(H2O)2]n or [Cd3(chdc)3(4-PyBIm)2(H2O)2]n, was synthesized hydrothermally from the reaction of Cd(CH3COO)2·2H2O with 2-(pyridin-4-yl)-1H-benzimidazole (4-PyBIm) and cyclohexane-1,4-dicarboxylic acid (1,4-chdcH2). The asymmetric unit consists of one and a half Cd(II) cations, one 4-PyBIm ligand, one and a half 1,4-chdc(2-) ligands and one coordinated water molecule. The central Cd(II) cation, located on an inversion centre, is coordinated by six carboxylate O atoms from six 1,4-chdc(2-) ligands to complete an elongated octahedral coordination geometry. The two terminal rotationally symmetric Cd(II) cations each exhibits a distorted pentagonal-bipyramidal geometry, coordinated by one N atom from 4-PyBIm, five O atoms from three 1,4-chdc(2-) ligands and one O atom from an aqua ligand. The 1,4-chdc(2-) ligands possess two conformations, i.e. e,e-trans-chdc(2-) and e,a-cis-chdc(2-). The cis-1,4-chdc(2-) ligands bridge the Cd(II) cations to form a trinuclear {Cd3}-based chain along the b axis, while the trans-1,4-chdc(2-) ligands further link adjacent one-dimensional chains to construct an interesting two-dimensional network.