Divanadium(V) complexes with 4-R-benzoic acid (1-methyl-3-oxo-butylidene)-hydrazides: Syntheses, structures and properties

In acetonitrile, reactions of bis(acetylacetonato)oxidovanadium(IV) ([VO(acac)2]) with 4-R-benzoylhydrazine in 1:1 mole ratio provide coordinatively symmetrical complexes (1–5) of the {OV(μ-O)VO}4+ motif in 40–47% yields. On the other hand, in methanol the same reactants provide complexes (6–10) containing the {OV(μ-OMe)2VO}4+ core in 37–50% yields. In both series of complexes, the ligand is the O,N,O-donor deprotonated Schiff base system 4-R-benzoic acid (1-methyl-3-oxo-butylidene)-hydrazide formed by template condensation of acac− with 4-R-benzoylhydrazine (R = H, Cl, OMe, NO2 and NMe2). All the complexes have been characterized by elemental analysis, magnetic and spectroscopic (IR, UV–Vis and NMR) measurements. Molecular structures of three representative complexes (4, 6 and 7) have been determined by X-ray crystallography. In each complex, the dianionic planar ligand is coordinated to the metal centre via the enolate-O, the imine-N and the O-atom of the deprotonated amide functionality. Cyclic voltammetric measurements in dichloromethane revealed that complexes 1–5 are redox inactive, while complexes 6–10 display a metal centred reduction in the potential range −0.06 to 0.0.32 V (versus Ag/AgCl).