Ligand and pH-Controlled ZnII bilayer coordination polymers based on biphenyl-3,3',4,4'-tetracarboxylate

Four novel Zn-II coordination polymers, [Zn(btc)(0.5)(H2O)](n) ((1)), {[Zn(btc)(0.5)(4,4'-bpy)(0.5)(H2O)]center dot 1.5H(2)O}(n) ((2)), {[Zn-2(H(2)btc)(2)(4,4'-bpy)(4)]center dot H2O}(n) ((3)), [Zn(H(2)btc)(bpe)](n) ((4)) [H(4)btc = biphenyl-3,3',4,4'-tetracarboxylic acid, 4,4'-bpy = 4,4'-bipyridine, and bpe = 1,2-bis(4-pyridyl)ethane], have been synthesized by hydrothermal reactions. Single-crystal X-ray structural analysis reveals that the four polymers exhibit different novel bilayer architectures. Complex 1 possesses a bilayer structure in which two helical layers are further pillared by (btc)(4-) ligands into a two-dimensional (2D) bilayer network. Complex 2 is an unusual 2D double-layered supramolecular motif generated by hydrogen bonding interactions of two single-layered networks. Complex 3 displays a 2D supramolecular bilayer network formed by the one-dimensional {[Zn-2(H(2)btc)(2)(4,4'-bpy)(4)]center dot H2O}(n) polymer. Complex 4 features a 2D double-layered framework in which two puckering single layers are linked by mu(2)-carboxylato groups of (H(2)btc)(2-) anions. The diverse structures illustrate rational adjustment of the second ligand, and the pH value is a good method to further design bilayer metal-organic compounds with novel structures and properties. In addition, the thermal stabilities and photoluminescence properties of 1-4 were also studied.