Solvothermal synthesis of coordination polymers at different temperatures and their luminescence studies

A new linker, [1,1':2',1 ''-terphenyl]-4',5'-dimethoxy-4,4 ''-dicarboxylic acid (H2L) has been used along with 4,4'-azobispyridine (azpy) as the co-linker to solvothermally synthesize six coordination polymers (CPs). These compounds are formulated as {[Zn(L)(azpy)(0.5)]center dot(0.5H(2)O)}(n) (1), {[Zn-2(L)(2)(azpy)]center dot(DMF)center dot(1.5H(2)O)}(n) (2), {[Zn(L)(bphy)]center dot(DMF)}(n) (3), [Cd(L)(azpy)(0.5)(DMF)(H2O)](n) (4), {[Co(L)(azpy)](2H(2)O)}(n) (5) and {[Co-3(L)(2)(bphy)(2)(HCOO)(2)(H2O)(2)](6DMF)(6H(2)O)}(n) (6) (bphy = 1,2-bis.4-pyridyl) hydrazine). Interestingly, 1 and 2 which are synthesized at 90 and 120 degrees C, respectively, are found to be orientation isomers. When the solvothermal reactions are carried out at 140 degrees C, the azo-bond in the co-linker azpy is reduced to bphy as found in 3 and 6. All the complexes exhibit an sql topology. They are characterized by X-ray crystallography, elemental analysis, thermogravimetry, powder X-ray diffraction and infrared spectroscopy. Solid state photoluminescence studies show an intra-ligand pi-pi* transition in each case.