Ligand-controlled Assembly of Cd(II) Metal-Organic Coordination Polymers Based on 3,5-Dinitrobenzoate and Flexible Bis(imidazole) Derivatives

Three new Cd(II) metal-organic coordination polymers, [Cd(bbi)(DNBA)2] (1), [Cd(bbbi)(DNBA)2] (2), and [Cd(dmbbbi)(DNBA)Cl]·0.38H2O (3) [HDNBA = 3,5-dinitrobenzoic acid, bbi = 1,1-(1,4-butanediyl)bis(imidazole), bbbi = 1,1-(1,4-butanediyl)bis(benzimidazole), and dmbbbi = 1,1-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole)], have been obtained from hydrothermal reactions of cadmium(II) chloride with the mixed ligands HDNBA and the three structurally related flexible bis(imidazole) derivatives. Single-crystal X-ray diffraction analyses have revealed that the dinuclear cadmium clusters acting as nodes interlinked by two μ2-carboxylic groups, are connected to four other clusters through bridging bbi (for 1) and bbbi (for 2) units to generate two extended two-dimensional (2-D) networks. Compound 3 features a 1-D zigzag chain structure. A systematic structural comparison of the title compounds indicates that the conformations and the steric hindrance of flexible bis(imidazole) derivatives each play an important role in the formation of the Cd(II) coordination polymers. The thermal stability of 1 and 2, and the luminescence behavior of 3 were also investigated.