Coordination polymers driven by 2,5-dibromoterephthalic acid and chelating co-ligands: Syntheses, structures and luminescent properties

Four coordination polymers, namely, [Zn (DBT) (4,4'-dmbpy) (H2O)](n) (1), [Co(DBT) (2,2'-bpy) (H2O)](n) (2), [Zn (DBT) (2,2'-bpy)](n) (3), [Zn (DBT)(0.5) (2,2'-bpy)(2)-(HDBT-)](n) (4) (H2DBT = 2,5-dibromoterephthalic acid, 4,4'-dmbpy = 4,4'-dimethyl-2,2'-bipyridyl and 2,2'-bpy = 2,2'-bipyridyl) have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, IR and thermogravimetric (TG) analysis. These four compounds remained stable until 150 degrees C, and the major quality loss (83-90%) occurred between 150 and 700 degrees C. In mixed ligands system, the main ligand H2DBT exhibits monodentate or bidentate bridging coordination modes and the auxiliary ligands 4,4'-dmbpy and 2,2'-bpy both possess bidentate chelate coordination modes. An objective of this study was to investigate the pivotal role of chelating ligands in the formation of low dimensional structures. As the bipyridyl ligands occupy the coordination site, compounds 1-3 all display two dimensional structures and 4 shows 1D chains, of which compounds 1 and 2 are isomorphic. The hydrogen bonds and IE-It stacking work together in the formation of 3D supramolecular structure of these four compounds. Besides, we investigated their photoluminescence properties in the solid state at room temperature. The compounds 1, 3 and 4 exhibited good fluorescence performance, and their strong emission peaks were located at 447 nm (lambda ex = 285 nm) for 1, 427 nm (lambda ex = 330 nm) for 3, and 412 nm (lambda ex = 310 nm) for 4.