Synthesis, Structure, and Characterization of Variable Chains in a Series of Transition Metal Coordination Compounds

Five new transition metal coordination polymers, [Zn-3(bipy)(TC)(6)] (1), [Co-3(bipy)(TC)(6)] (2), [Co(bipy)(TC)(2)] (3), [Cd(bipy)(TC)(2)] (4), and [Cu-2(bipy)(TC)(4)] (5) (bipy = 4,4'-bipyridine; TC = 3-thiophenecarboxylate), with chain structures, were solvothermally synthesized in high yields under mild reaction conditions. While compounds 1, 2, and 3 reveal peddle wheel-like chain structures, compounds 4 and 5 exhibit ladder-like chain backbones. The organic bipy ligand was utilized as a linker that connects each cluster consisting of the corresponding metal cation and the TC ligand in each infinite chain. While the frameworks of compounds 1, 2, 3, and 5 are thermally robust up to ca. 300 degrees C, that of compound 4 reveals thermal stability to ca. 250 degrees C. The observed band gaps of the title compounds range from 1.94 to 3.64 eV. Photoluminescence (PL) properties arising from the intraligand as well as the ligand-to-metal charge transfer were studied for compounds 1 and 4. The magnetic behavior of compound 2 is described by a coupled linear trimer, while those of compounds 3 and 5 turned out to be coupled spin dimers.