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

Dark-brown complexes of {OV(mu-O)VO}(4+) with the general formula [(VOL)(2) O] 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 functional ities) in acetonitrile. The infrared spectra of these complexes are consist ent with the dianionic form of the ligands. The electronic spectral profile s are very similar and display strong absorptions in the range 425-263 nm d ue to ligand-to-metal charge transfer and intraligand transitions. The prot on NMR spectra suggest that in solution the two ligands in each complex are magnetically equivalent. The complexes are redox active and display a redu ction response in the potential range -0.28-0.47 V (vs. Ag/AgCl). The molec ular 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 essen tially in a square-pyramidal O4N coordination sphere. The O, N, O-donor lig and and the bridging oxygen atom constitute the square plane and the oxo gr oup occupies the apical position. The metal center is displaced from the ba sal plane towards the apical oxo group by 0.44-0.57 Angstrom. The V-O-V bri dge angles in the complexes are very similar and within the range 112.86(13 ) to 115.89(12)degrees.