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(L1)0.5(H2O)] (1), [Zn2(BPTC)(L2)]·H2O (2), [Zn2(BPTC)(L3)2]·3H2O (3), [Zn2.5(BPTC)(L4)(OH)(H2O)] (4), [Zn2(BPTC)(L5)(H2O)2]·3H2O (5), [Cd2(BPTC)(L5)(H2O)]·H2O (6), and [Cd(BPTC)0.5(L6)]·H2O (7), where L1 = 4,4′-bis(imidazol-1-ylmethyl)bibenzene, L2 = 4,4′-bis(imidazol-1-ylmethyl)benzene, L3 = 1,4-bis(imidazol-1-yl)butane, L4 = 1,4-bis(2-ethyl-imidazol-1-yl)butane, L5 = 1,3-bis[2-(2-pyridyl)imidazol-1-ylmethyl]benzene, L6 = 1,2-bis[2-(2-pyridyl)imidazol-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 1 exhibits a (4,6)-connected network with a (44·62)(44·610·8) topology formed by L1 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 L3−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 L4−Zn sheets are connected by BPTC pillars to generate a 3D framework with a distorted α-Po topology. Compound 5 shows infinite chains. Compound 6 shows two kinds of novel infinite chains which are linked by π−π stacking interactions to form 2D supramolecular sheets. Compound 7 is a (3,4)-connected framework with a (62·8)2(62·84) topology. The structural differences among 14 indicate the importance of the flexibility of the ligands (L1−L4) for the framework formation of the coordination polymers. By varying the angular feature of the ligands (L5 and L6), compounds 57 have been separated completely. In additon, the luminescent properties of these compounds are discussed.