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 (H2L1), benzene-1,2-dicarboxylic acid (H2L2), and biphenyl-4,4'-dicarboxylic acid (H2L3)] has allowed the rational design of three novel Cd(II) coordination polymers, [Cd-3(Dpq)(3)(L-1)(3)]center dot 4.5H(2)O (1), [Cd(Dpq)(L-2)(H2O)] (2), and [Cd-2(Dpq)(2)(L-3)(2)]center dot 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 alpha-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.