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

Five new transition metal coordination polymers, [Zn₃(bipy)(TC)₆] (1), [Co₃(bipy)(TC)₆] (2), [Co(bipy)(TC)₂] (3), [Cd(bipy)(TC)₂] (4), and [Cu₂(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 °C, that of compound 4 reveals thermal stability to ca. 250 °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.