Oxovanadium(IV,V) complexes with 2-acetylpyridine-2-furanoylhydrazone (Hapf) as ligand.: X-ray crystal structures of [VO2(apf)] and [V2O2(μ-O)2(apf)2]

The preparation of oxovanadium(IV,V) coordination compounds with 2-acetylpyridine-2-furanoylhydrazone (Hapf) is described. [VO(apf)(acac)] was prepared from oxovanadium(IV) diacetylacetonate [VO(acac)(2)] by reaction with Hapf in methanol or dichloromethane. The complex is paramagnetic and its EPR spectrum is consistent with an octahedral coordination for the vanadium(IV) atom. Voltammetry studies of [VO(apf)(acac)] indicate an irreversible oxidation, in agreement with the chemical behavior of the compound in solution. The vanadium(IV) complex undergoes slow oxidation in alcoholic solution, losing the acetylacetonate ligand to form [VO2(apf)] and [V2O2(mu-O)(2)(apf)(2)]. The crystal structures of these last compounds were determined by X-ray diffraction methods. [V2O2(mu-O)(2)(apf)(2)] crystallizes monoclinic [P2(1)/c, Z = 2, a = 817.400(10), b = 1650.90(3), c = 984.70(2) pm, beta = 112.7190(10)degrees]. The crystal structure consists of dimeric units, in which two mu-oxo ligands subtend asymmetric bridges between the vanadium atoms in a very distorted octahedral coordination. In the crystal of [VO2(apf)], orthorhombic [Pnma, Z = 4, a 1630.000(10), b = 675.10(4), c = 1136.40(2) pm], the vanadium(V) atom is pentacoordinated.