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(μ‐O)₂(apf)₂]. The crystal structures of these last compounds were determined by X‐ray diffraction methods. [V₂O₂(μ‐O)₂(apf)₂] crystallizes monoclinic [P2₁/c, Z = 2, a = 817.400(10), b = 1650.90(3), c = 984.70(2) pm, β = 112.7190(10)°]. The crystal structure consists of dimeric units, in which two μ‐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.