Assembly of anion-controlled cadmium(II) coordination polymers based on flexible bis(imidazole) derivative

Four Cd(II) metal–organic complexes, namely, [Cd(Cl)2(bbdmbm)] (1), [Cd(NO3)(N3)(bbdmbm)1.5] (2), [Cd(BBA)2(bbdmbm)(H2O)] (3), [Cd(DNBA)2(bbdmbm)] (4), (bbdmbm = 1,1-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole), HBBA = 4-bromobenzoic acid, and HDNBA = 3,5-dinitrobenzoic acid) have been obtained from hydrothermal reactions of different Cd(II) salts with the mixed ligands of bbdmbm and five anions (Cl−, NO3−, N3−, BBA and DNBA). Single crystal X-ray diffraction analyses reveal that the four complexes exhibit different structures. Complex 1 possesses a one-dimensional (1D) helical chain, which is finally extended into a two-dimensional (2D) supramolecular structure through π–π stacking interactions. Complex 2 shows a 1D ladderlike chain bridged by bbdmbm ligands with two kinds of coordination conformations. Complex 3 is a 1D coordination polymer and is ultimately extended into a 2D supramolecular network through H-bonding interactions. Complex 4 displays a dinuclear cluster, which is finally packed into a three-dimensional (3D) supramolecular framework through three kinds of π–π stacking interactions. The Cd(II) exhibits four different coordination modes in complexes 1–4, respectively. The results indicate that the anion ligands with different steric hindrance and size play important roles in the coordination modes of Cd(II) and construction of the title complexes, leading to the structural diversity. In addition, the conformations of bbdmbm ligand also show some effect on the final structures. Fluorescence properties of complexes 1–4 are reported in this paper.