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 (H 2 O)] ( 1 ), [Zn 2 (BPTC)(L 2 )]·H 2 O ( 2 ), [Zn 2 (BPTC)(L 3 ) 2 ]·3H 2 O ( 3 ), [Zn 2.5 (BPTC)(L 4 )(OH)(H 2 O)] ( 4 ), [Zn 2 (BPTC)(L 5 )(H 2 O) 2 ]·3H 2 O ( 5 ), [Cd 2 (BPTC)(L 5 )(H 2 O)]·H 2 O ( 6 ), and [Cd(BPTC) 0.5 (L 6 )]·H 2 O ( 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)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 (4 4 ·6 2 )(4 4 ·6 10 ·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 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 (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.