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

Reaction of VIVOCl2 in strongly acidic aqueous solution with either (NH4)(2)SO3 or Na2SO3 and Bu4NBr at similar to 70 degrees C in the pH range 2.5-4.5 gives the clusters (NH4)(2){[V-4(IV)(mu(4)-O)(2)(mu(3)-OH)(2)]((VO)-O-IV)(2)(mu(3)-SO3)(4)O-4(H2O)(2)} and (n-Bu4N)(2){[V-4(IV)(mu(4)-O)(2)(mu(3)-OH)(2)]((VO)-O-IV)(2)(mu(3)-SO3)(4)O-4(H2O)(2)}, respectively. Reaction of (NH4VO3)-O-V with (NH4)(2)SO3 resulted in the isolation of the first compound. When the latter reaction is carried out in the presence of MgO, compound (NH4)[(VO)-O-IV(SO3)(1.5)H2O](infinity)center dot 2.5H(2)O was isolated instead. Compound (n-Bu4N)(2){[V-4(IV)(mu(4)-O)(2)(mu(3)-OH)(2)]((VO)-O-IV)(2)(mu(3)-SO3)(4)O-4(H2O)(2)} and (NH4)[(VO)-O-IV(SO3)(1.5)H2O](infinity)center dot 2.5H(2)O were characterized by X-ray structure analysis. The crystal structure of species (n-Bu4N)(2){IV4IV(mu(4)-O)(2)(mu(3)-OH)(2)]((VO)-O-IV)(2)(mu(3)-SO3)(4)O-4(H2O)(2)} revealed a unprecedented hexanuclear cluster consisting of a cubane core [M-4(mu(4)-O)(2)(mu(3)- OH)(2)] connected to two other metal atoms through the core oxo-groups and four mu(3)-SO3 bridges. Compound (NH4)[VIVO(SO3)(1.5)H2O](infinity)center dot 2.5H(2)O represents a rare example of an open-framework species prepared under mild conditions. Cyclic voltammetric examination of compound (n-Bu4N)(2){[IV4IV(mu(4)-O)(2)(mu(3)-OH)(2)]((VO)-O-IV)(2)(mu(3)-SO3)(4)O-4(H2O)(2)] revealed a redox process which was assigned to the oxidation of one core of vanadium(IV) to vanadium(V).