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Pure Appl. Chem., 2005, Vol. 77, No. 9, pp. 1529-1538

Oxovanadium(IV)-sulfite compounds: Synthesis and structural and physical studies

George I. Chilas1, Haralampos N. Miras1, Manolis J. Manos1, J. Derek Woollins2, Alexandra M. Z. Slawin2, Marios Stylianou3, Anastasios D. Keramidas3 and Themistoklis A. Kabanos1

1 Department of Chemistry, Section of Inorganic and Analytical Chemistry, University of Ioannina, 45110 Ioannina, Greece
2 Department of Chemistry, University of St. Andrews, UK
3 University of Cyprus, 1678 Nicosia, Cyprus

Abstract: Reaction of VIVOCl2 in strongly acidic aqueous solution with either (NH4)2SO3 or Na2SO3 and Bu4NBr at ~70°C in the pH range 2.5-4.5 gives the clusters (NH4)2{[V4IV(μ4-O)2(μ3-OH)2](VIVO)2(μ3-SO3)4O4(H2O)2} and (n-Bu4N)2{[V4IV(μ4-O)2(μ3-OH)2](VIVO)2(μ3-SO3)4O4(H2O)2}, respectively. Reaction of NH4VVO3 with (NH4)2SO3 resulted in the isolation of the first compound. When the latter reaction is carried out in the presence of MgO, compound (NH4)[VIVO(SO3)1.5H2O].2.5H2O was isolated instead. Compound (n-Bu4N)2{[V4IV(μ4-O)2(μ3-OH)2](VIVO)2(μ3-SO3)4O4(H2O)2} and (NH4)[VIVO(SO3)1.5H2O].2.5H2O were characterized by X-ray structure analysis. The crystal structure of species (n-Bu4N)2{[V4IV(μ4-O)2(μ3-OH)2](VIVO)2(μ3-SO3)4O4(H2O)2} revealed a unprecedented hexanuclear cluster consisting of a cubane core [M4(μ4-O)2(μ3-OH)2] connected to two other metal atoms through the core oxo-groups and four μ3-SO3 bridges. Compound (NH4)[VIVO(SO3)1.5H2O].2.5H2O represents a rare example of an open-framework species prepared under mild conditions. Cyclic voltammetric examination of compound (n-Bu4N)2{[V4IV(μ4-O)2(μ3-OH)2](VIVO)2(μ3-SO3)4O4(H2O)2} revealed a redox process which was assigned to the oxidation of one core of vanadium(IV) to vanadium(V).