A family of dinuclear vanadium(V) complexes containing the {OV(μ- O)VO} < sup > 4+ < /sup > core: Syntheses, structures, and properties

Abstract

Dark-brown complexes of {OV(μ-O)VO}4+ with the general formula [(VOL)2O] were isolated from reactions of bis(acetylacetonato)oxovanadium(IV) and aroylhydrazones of salicylaldehyde or of 5-methoxysalicylaldehyde (H2L, two H stand for the dissociable protons at the phenol and the amide functionalities) in acetonitrile. The infrared spectra of these complexes are consistent with the dianionic form of the ligands. The electronic spectral profiles are very similar and display strong absorptions in the range 425 - 263 nm due to ligand-to-metal charge transfer and intraligand transitions. The proton NMR spectra suggest that in solution the two ligands in each complex are magnetically equivalent. The complexes are redox active and display a reduction response in the potential range - 0.28 - 0.47 V (vs. Ag/AgCI). The molecular structures of the complexes were determined by X-ray crystallography. The deprotonated dianionic planar ligands coordinate the metal ions through the phenolate-O, the imine-N, and the amide-O atoms forming a six-membered and a five-membered chelate ring. The metal ions in each complex are essentially in a square-pyramidal O4N coordination sphere. The O, N, O-donor ligand and the bridging oxygen atom constitute the square plane and the oxo group occupies the apical position. The metal center is displaced from the basal plane towards the apical oxo group by 0.44-0.57 Å. The V-O-V bridge angles in the complexes are very similar and within the range 112.86(13) to 115.89(12)°.