Three Novel Cd(II) Metal−Organic Frameworks Constructed from Mixed Ligands of Dipyrido[3,2-d:2‘,3‘-f]quinoxaline and Benzene-dicarboxylate:  From a 1-D Ribbon, 2-D Layered Network, to a 3-D Architecture

The use of dipyrido[3,2- d:2‘,3‘- f ]quinoxaline ( Dpq ) combined with three structurally related benzene-dicarboxylic acid ligands [benzene-1,3-dicarboxylic acid (H 2 L 1 ), benzene-1,2-dicarboxylic acid (H 2 L 2 ), and biphenyl-4,4‘-dicarboxylic acid (H 2 L 3 )] has allowed the rational design of three novel Cd(II) coordination polymers, [Cd 3 ( Dpq ) 3 ( L 1 ) 3 ]·4.5H 2 O ( 1 ), [Cd( Dpq )( L 2 )(H 2 O)] ( 2 ), and [Cd 2 ( Dpq ) 2 ( L 3 ) 2 ]·1.5H 2 O ( 3 ), which were hydrothermally synthesized and structurally determined by X-ray analysis. Compound 1 features a 1-D ribbonlike structure, compound 2 shows novel 2-D four-connected networks, and compound 3 possesses an interesting 6-connected 2-fold interpenetrated 3-D α-Po-related architecture. The Dpq ligand takes a chelating coordination mode while the other two nitrogen atoms did not coordinate to the Cd(II) ions. In these complexes, the three benzene−dicarboxylate ligands are able to link Cd(II) ions in various coordination modes, giving rise to 1-, 2-, and 3-dimensional Cd complexes, respectively. In addition, complexes 1 − 3 exhibit blue/green emission in the solid state at room temperature.