Metal-controlled assembly of coordination polymers with the flexible ligand 1,1′-biphenyl-2,2′-dicarboxylate acid

To determine the influence of metal ions on the formation of metal-organic frameworks, five new coordination polymers, [Pb-6(dpa)(4)O-2](n) (1), [Ag-2(dpa)](n) (2), [Nd-2(dpa)3(H2O)(2)](n) (3), [Zn(dpa)(H2O)](n) (4), and [Cd-2(dpa)(2)(phen)(2)(H2O)(2)](n) (5), have been hydrothermally synthesized from 1,1'-biphenyl-2,2'-dicarboxylate acid (dpa). Complex 1 is a one-dimensional chain structure constructed from a new building unit, Pb6O18, which is connected by four different dpa molecules. Complex 3 is also a one-dimensional chain structure but is composed of a different building unit bridged by three dpa molecules. This complex is further extended into a two-dimensional supramolecular framework. Like complex 3, complex 4 is a two-dimensional supramolecular framework, which is connected by one-dimensional chains through pi-pi interactions and hydrogen bonding interactions. Complex 5 is a three-dimensional metal-organic supramolecular coordination polymer that possesses rectangular cavities. Different from the above four complexes, complex 2 is a two-dimensional covalence structure. To our knowledge, this is the first two-dimensional coordination polymer composed of metal ions and the dpa ligand. Furthermore, at room temperature, complex 4 exhibits strong photoluminescence.