Hydrothermal synthesis, crystal structures and photoluminescent properties of four cadmium(II) coordination polymers derived from diphenic acid and auxiliary ligands

Four novel metal coordination polymers, [Cd(dpa)(H2O)]n (1), [Cd(dpa)(2,2′-bipy)]n (2), {[Cd2(dpa)2(4,4′-bipy)3](4,4′-bipy)(H2O)2}n (3) and [Cd(dpa)(bim)2(H2O)]}n (4) (H2dpa = 2,4′-biphenyl-dicarboxylic acid, 2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine, bim = benzimidazole), have been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction. Single-crystal X-ray analyses reveal that the 2,4′-diphenic acids acts as bridging ligands, exhibiting rich coordination modes to link metal ions: bis-monodentate, bidentate chelating, chelating/bridging, monoatomic bridging and monodentate modes. In addition, the luminescent properties for compound 1–4 are also investigated in this work.