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), [Zn_2.5(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 1–4 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 5–7 have been separated completely. In additon, the luminescent properties of these compounds are discussed.