Ligand and pH-Controlled Zn^II Bilayer Coordination Polymers Based on Biphenyl-3,3‘,4,4‘-tetracarboxylate

Four novel ZnII coordination polymers, [Zn(btc)0.5(H2O)]n (1), {[Zn(btc)0.5(4,4‘-bpy)0.5(H2O)]·1.5H2O}n (2), {[Zn2(H2btc)2(4,4‘-bpy)4]·H2O}n (3), [Zn(H2btc)(bpe)]n (4) [H4btc = 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 {[Zn2(H2btc)2(4,4‘-bpy)4]·H2O}n polymer. Complex 4 features a 2D double-layered framework in which two puckering single layers are linked by μ2-carboxylato groups of (H2btc)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.