A new one-dimensional Cd^II coordination polymer incorporating 2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylate)

Imidazole-4,5-dicarboxylic acid (H₃IDC) and its derivatives are widely used in the preparation of new coordination polymers owing to their versatile bridging coordination modes and potential hydrogen-bonding donors and acceptors. A new one-dimensional coordination polymer, namely catena-poly[[diaquacadmium(II)]-μ₃-2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylato)], [Cd(C₁₆H₆N₄O₈)_0.5(H₂O)₂]_n or [Cd(H₂Phbidc)_1/2(H₂O)₂]_n, has been synthesized by the reaction of Cd(OAc)₂·2H₂O (OAc is acetate) with 2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylic acid) (H₆Phbidc) under solvothermal conditions. In the polymer, one type of Cd ion (Cd1) is six-coordinated by two N atoms and two O atoms from one H₂Phbidc^4- ligand and by two O atoms from two water molecules, forming a significantly distorted octahedral CdN₂O₄ coordination geometry. In contrast, the other type of Cd ion (Cd2) is six-coordinated by two N atoms and two O atoms from two symmetry-related H₂Phbidc^4- ligands and by two O atoms from two symmetry-related water molecules, leading to a more regular octahedral coordination geometry. The Cd1 and Cd2 ions are linked by H₂Phbidc^4- ligands into a one-dimensional chain which runs parallel to the b axis. In the crystal, the one-dimensional chains are connected through hydrogen bonds, generating a two-dimensional layered structure parallel to the ab plane. Adjacent layers are further linked by hydrogen bonds, forming a three-dimensional structure in the solid state.