Synthesis and structures of two-dimensional coordination polymers constructed by metal salts and 4,4′-bipyridine

Abstract

Two nitrate compounds, [Cu(4,4′-bpy) 2(NO 3) 2]·(paba) 3 ( 1) and [Cd(4,4′-bpy) 2(H 2O) 2](NO 3) 2·4H 2O ( 2) (4,4′-bpy=4,4′-bipyridine; paba=4-aminobenzic acid), were obtained from the reactions of different metal salts and 4,4′-bpy. Compounds 1 and 2 are made up of two-dimensional square [M 4(4,4′-bpy) 4] grids in which the cavity has dimensions of 11.01×11.02 and 11.69×11.81 Å for 1 and 2, respectively. In 1, the guest paba molecules are enclathrated in the hydrophobic host cavities or situated between the coordination layers and interlinked into one-dimensional hydrogen-bonding chains through hydrogen bonding and CH⋯π interactions, which further interpenetrate and contact the square grids through their functional moieties (pyridyl rings, amine groups and carboxylic groups), resulting in a new three-dimensional molecular network. In 2, the lattice water molecules and nitrate ions are situated between the coordination layers, and extensive hydrogen bonds between the host grid and guest molecules extend the two-dimensional coordination layer into a three-dimensional molecular network.