Structure characterization of several oxalate-bridged transition-metal coordination polymers

Four oxalate-bridged transition-metal supramolecular compounds [Co2(im)4(ox)2] 1, [Co(im)2(ox)] 2, [Mn(2,2′-bpy)(ox)] 3 and [Fe(H2O)2(ox)] 4 (im, imidazole; ox, oxalate; bpy, bipyridine) were obtained from the simple hydrothermal reactions of Mn+oxL (M, transition metal; L, aromatic N-donor ligand) system. They all exhibit the 1-D chain structures, consisting of the ML22+ (or ML2+) units linked by oxalate bridges. Interestingly, the 1-D oxalate chains in the title compounds are further self-assembled into the 3-D supramolecular networks through the interchain various secondary bonding interactions. Because the ML22+ units adopt the different configuration, the oxalate chains show either zigzag type as in compounds 1–3 or linear type as in compound 4. Compounds 1 and 2 are isomeric, and only in packing modes of interchain im molecules there exists the difference.