Three Heterometallic Coordination Polymers Containing Lead(II): Syntheses, Crystal Structures, and Fluorescence Properties

Three coordination polymers [Pb-2(nipt)(2)(NiL)(2)] (1), [Pb(tpt)(NiL)]center dot 2H(2)O (2), and [Pb-2(ipt)(2)(NiL)(2)] (3) (ML, H2L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien, H(2)nipt = 5-nitroisophthalic acid, H(2)tpt = terephthalic acid, H(2)ipt = isophthalic acid) were synthesized by solvothermal methods and characterized by single-crystal X-ray diffraction. Complex 1 exhibits a zig-zag chain consisting of Pb2Ni2 units with oxamide and 5-nitro isophthalate bridges, whereas complex 2 possesses a double chain with oxamide and terephthalate bridges. Complexes 1 and 2 have a 2D supra-molecular architecture formed by intermolecular interactions and hydrogen bonds. Complex 3 exhibits a two-dimensional network structures formed by Pb4Ni4 units via oxamide and isophthalate bridges. In complexes 1-3, the arrangement of donor atoms suggest that the coordination around the lead(II) atoms is hemi-directed. The different steric hindrance of bridged ligands, and lone pair electrons effect of lead(II) ion cooperatively influence nipt, tpt and ipt displaying in diverse connecting modes and further result in different structures. Additionally the fluorescence properties of compounds 1-3 are discussed.