Synthesis, characterization and crystal structure of the new pentahydrate of bis-(2,2 ‘-bipyridine-kappa N-2,N ‘)(oxalato-kappa O-2(1),O-2)nickel(II).

The reaction of NiCl2, K2C2O4 center dot H2O and 2,2′-bipyridine (bpy) in water-ethanol solution at 281 K yields light-purple needles of the new pentahydrate of bis(2,2′-bipyridine)oxalato-nickel(II), [Ni(C2O4)(C10H8N2)(2)]center dot 5H(2)O or [Ni(ox)(bpy)(2)]center dot-5H(2)O, while at room temperature, deep-pink prisms of the previously reported tetrahydrate [Ni(ox)(bpy)(2)]center dot 4H(2)O [Roman, Luque, Guzman-Miralles & Beitia (1995), Polyhedron, 14, 2863-2869] were gathered. The asymmetric unit in the crystal structure of the new pentahydrate incorporates the discrete molecular complex [Ni(ox)(bpy)(2)] and five solvent water molecules. Within the complex molecule, all three ligands are bonded as chelates. The complex molecules are involved in an extended system of hydrogen bonds with the solvent water molecules. Additionally, pi-pi interactions also contribute to the stabilization of the extended structure. The dehydration of the pentahydrate starts at 323 K and proceeds in at least two steps as determined by thermal analysis.