Cadmium(II) complexes with 3,5-di(1H-imidazol-1-yl)benzoate: topological and structural diversity tuned by counteranions

Abstract

Four new coordination polymers [Cd(L)(OAc)]·H₂O (1), [Cd(L)(µ₂-OH)]·H₂O (2), [Cd₂(L)₂(µ₃-SO₄)(H₂O)₂]·5H₂O (3) and [Cd(L)₂]·H₂O (4) with different structures and topologies were obtained by solvo/hydrothermal reactions of varied Cd(II) salts with 3,5-di(1H-imidazol-1-yl)benzoic acid (HL) and 1,3-bis(4-pyridyl)propane (bpp). The structures of 1–4 were characterized by single-crystal X-ray diffraction analysis and the results showed that no bpp ligands were incorporated in the resulting complexes, and more interestingly, complexes 1–3 were obtained by reactions of metal to ligand ratio of 1 : 1, however, when the reactions were carried out with a metal to ligand ratio of 1 : 2, the resulting complexes had the same structure, namely [Cd(L)₂]·H₂O (4). In contrast to the 2D network with 6³-hcb topology of complex 1 with acetate as terminal ligand, complex 2 is a 3D (4,6)-connected net with µ₂-hydroxyl bridging group. Complex 3 is an unprecedented 3D self-penetrating (3,4,5)-connected net with each sulfate as a µ₃-bridge to link three Cd(II) atoms, and complex 4 is a 3D self-penetrating (3,5)-connected net formed by two alternate chiral helical chains linking 2-fold interpenetrating 2D (4,8²) nets. The results showed that the L⁻ ligand has varied coordination modes and the counteranions have a great impact on the structure of the complexes.