Synthesis, characterization and crystal structure of the new pentahydrate of bis(2,2′-bipyridine-κ² N,N′)(oxalato-κ² O ¹,O ²)nickel(II)

Abstract

The reaction of NiCl2, K2C2O4·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)oxalatonickel(II), [Ni(C2O4)(C10H8N2)2]·5H2O or [Ni(ox)(bpy)2]·5H2O, while at room temperature, deep-pink prisms of the previously reported tetrahydrate [Ni(ox)(bpy)2]·4H2O [Román, Luque, Guzmán-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, π-π 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.

[Ni(bpy)(ox)]: a candidate in the class of Haldane gap systems (bpy = 2,2ʹ-bipyridine, ox = oxalate)

“…As a consequence of the relatively short bis-chelating oxalate bridging, neighboring Ni(II) ions within the chain in 1 are much closer (5.380(7) Å) than in Ni(en) 2 Ni(CN) 4 in which the paramagnetic Ni(II) ions are linked by long cyanidocomplex bridging (9.940(2) Å)[37].The experimental Ni-O and Ni-N distances in 1 are 2.077(6)-2.109(14) and 2.094(20)-2.239(19) Å, respectively. Taking into account the limitations of the Rietveld method, the obtained values are in an acceptable range; in a similar [Ni(bpy) 2 (ox)]⋅5H 2 O, the Ni-N and Ni-O bonds are 2.0720(13)-2.1001(13) and 2.0359(11)-2.0673(12) Å, respectively[38].…”