Syntheses, crystal structures and properties of four novel coordination polymers assembled from versatile 1,2,3,5-benzenetetracarboxylic acid

Abstract

Four novel metal–organic coordination polymers constructed from 1,2,3,5-benzenetetracarboxylic acid, namely [Cu3(Hbtec)2(H2O)6]·2H2O (1), [Co2(btec)(H2O)2] (2), [Zn2(btec)(H2O)2] (3) and [Cd4(btec)2(H2O)5] (4) (H4btec=1,2,3,5-benzenetetracarboxylic acid), have been synthesized by hydrothermal methods and characterized by elemental analysis, IR, TGA and single crystal X-ray diffraction. Complex 1 is a two-dimensional double layer, while three dimensional framework structures are observed for complexes 2–4. The metal atoms are bridged via short connecting μ2-O-carboxylate atoms into dimers in the four different complexes. Interestingly, the dimers connect Hbtec bridged binuclear units into a one dimensional chain and further into a two-dimensional double layer in complex 1, while the metal ions are connected by a short bridge from μ2-O-carboxylate atoms and a long bridge from an adjacent carboxylate into a one dimensional metal carboxylate chain in complexes 2–4. In complexes 2 and 3, each btec ligand is coordinated through three metal carboxylate chains into a metal carboxylate layer, and further into a three-dimensional framework. In complex 4, both a one-dimensional single Cd-carboxylate chain as well as a one-dimensional double Cd-carboxylate chain appear, the two different chains are joined by the ligands into a three dimensional framework. The thermal stabilities and photoluminescent properties of complexes 1–4 were examined. Complexes 3 and 4 display strong room temperature photoluminescence in the visible region, which may be assigned to a ligand-to-metal charge-transfer.