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The Oxalate-bridged Antiferromagnetically Coupled [Cu^IICu^II] and [Ni^IINi^II] Systems

In the rational approaches to the design and synthesis of various metal-organic coordination networks with specific chemical and physical properties, a key role belongs to the nature of the metal ion and the geometry, flexibility and coordination preferences of the bridging ligands. The oxalate C_2O_4^2– anion, having rich binding facilities and capabilities of mediating exchange interaction between the metal centres, has appeared as a very useful bridging ligand in the synthesis of a variety of homo- and heterometallic compounds with attractive new architectures and interesting magnetic properties. As a continuation of our research work on polynuclear transition metal complexes, two novel oxalate-bridged species have been synhesized: a homodinuclear Cu^IICu^II complex, [Cu(bpy)Cl(µ -C_2O_4)Cu(bpy)Cl] (1) (bpy = 2, 2'-bipyridine) and a heterometallic Ni, Nb compound, containing homodinuclear Ni^IINi^II units, [{; Ni(bpy)_2}; _2(μ -C_2O_4)]_3[NbO(C_2O_4)_3]_2• 24H_2O (2). The new compounds have been characterized by means of chemical and TG/DTA analysis, infrared spectroscopy, magnetic susceptibility measurements and by single crystal X-ray diffraction method. Each copper(II) atom in 1 displays a square-pyramidal coordination, whereas nickel(II) atoms in 2 are placed in a slightly distorted octahedral environment. The analysis of magnetic susceptibility data (1.8– 290 K) reveals the existence of antiferromagnetic exchange interaction between the metal centres in oxalate-bridged units of 1 and 2.

oxalate-bridged ; crystal structure ; magnetic susceptibility ; antiferromagnetic

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