Two new two-dimensional coordination polymers based on isophthalate and a flexible N-donor ligand containing benzimidazole and pyridine rings: synthesis, crystal structures and a solid-state UV-Vis study.

In coordination chemistry and crystal engineering, many factors influence the construction of coordination polymers and the final frameworks depend greatly on the organic ligands used. N-Donor ligands with diverse coordination modes and conformations have been employed to assemble metal-organic frameworks. Carboxylic acid ligands can deprotonate completely or partially when bonding to metal ions and can also act as donors or acceptors of hydrogen bonds and are thus good candidates for the construction of supramolecular architectures. Two new transition metal complexes, namely poly[diaqua(μ4 -1,4-bis{[1-(pyridin-3-ylmethyl)-1H-benz[d]imidazol-2-yl]methoxy}benzene)bis(μ2 -isophthalato)dicobalt(II)], [Co(C8 H4 O4 )(C34 H28 N6 O2 )0.5 (H2 O)]n , (1), and poly[diaqua(μ4 -1,4-bis{[1-(pyridin-3-ylmethyl)-1H-benz[d]imidazol-2-yl]methoxy}benzene)bis(μ2 -isophthalato)dicadmium(II)], [Cd(C8 H4 O4 )(C34 H28 N6 O2 )0.5 (H2 O)]n , have been constructed using a symmetric N-donor ligand and a carboxylate ligand under hydrothermal conditions. X-ray crystallographic studies reveal that complexes (1) and (2) are isostructural, both of them exhibiting three-dimensional supramolecular architectures built by hydrogen bonds in which the coordinated water molecules serve as donors, while the O atoms of the carboxylate groups act as acceptors. Furthermore, (1) and (2) have been characterized by elemental, IR spectroscopic, powder X-ray diffraction (PXRD) and thermogravimetric analyses. The UV-Vis absorption spectrum of complex (1) has also been investigated.