Structures and luminescent properties of seven coordination polymers of zinc(II) and Cadmium(II) with 3,3',4,4'-benzophenone tetracarboxylate anion and bis(imidazole)

Seven coordination polymers, namely [Zn(BPTC)(0.5)(L-1)(0.5)(H2O)] (1), [Zn-2(BPTC)(L-2)]center dot H2O (2), [Zn-2(BPTC)(L-3)(2)]center dot 3H(2)O (3), [Zn-2.5(BPTC)(L-4)(OH)(H2O)](4), [Zn-2(BPTC)(L-5)(H2O)(2)]center dot 3H(2)O (5), [Cd-2(BPTC)(L-5)(H2O)]center dot H2O (6), and [Cd(BPTC)(0.5)(L-6)]center dot H2O (7), where L-1 = 4,4'-bis(imidazol-1-ylmethyl)bibenzene, L-2 = 4,4'-bis(imidazol-1-ylmethyl)benzene, L-3 = 1,4-bis(imidazol- 1-yl)butane, L-4 = 1,4-bis(2-ethyl-imidazol-1-yl)butane, L-5 = 1,3-bis [2-(2-pyridyl)imidazol-1-ylmethyl]benzene, L-6 = 1,2-bis[2-(2-pyridyl)im idazol-1-ylmethyl]benzene, and BPTC = 3,3',4,4'-benzophenone tetracarboxylate ligand, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric analyses. The structure of I exhibits a (4,6)-connected network with a (4(4)center dot 6(2)) (4(4) center dot 6(10)center dot 8) topology formed by L-1 ligands connecting BPTC-Zn sheets. The structure of 2 is a chiral 3D network in which there exists a Zn-O helical chain which may transmit the chirality to the whole framework. In compound 3, multicarboxylate ligands link L-3-metal helical chains to generate a layer which is further connected by intermolecular H bonds to form a 3D supramolecular structure. In compound 4, the L-4-Zn sheets are connected by BPTC pillars to generate a 3D framework with a distorted alpha-Po topology. Compound 5 shows infinite chains. Compound 6 shows two kinds of novel infinite chains which are linked by pi-pi stacking interactions to form 2D supramolecular sheets. Compound 7 is a (3,4)-connected framework with a (6(2). 8)(2)(6 (2).8(4)) topology. The structural differences among 1-4 indicate the importance of the flexibility of the ligands (L-1-L-4) for the framework formation of the coordination polymers. By varying the angular feature of the ligands (L 5 and L 6), compounds 5-7 have been separated completely. In additon, the luminescent properties of these compounds are discussed.