Novel unsymmetrical and symmetrical mononuclear and insoluble polynuclear oxo-vanadium(IV)–Schiff base complexes were prepared and characterized by physico- chemical method. The complexes [VO(5-x-6-y- Sal)(5-x-6-y-Sal)en)] (where x, x= H, Br, NO2 and y, y= H, OMe) were obtained in monomeric form while for x or x= NO2 polymeric form produced. All of the six membered N-N chelating ring in the [VO(5-x-6-y- Sal)(5-x-6-y-Sal)Pn)] were obtained and characterized as polynuclear complexes, were constituted from monomer units. The tetradentate N2O2-Schiff base ligands being coordinated in the equatorial plane of oxovanadium( IV). Electrochemical and spectroscopic data (uv-vis and IR) are related and suggested that they depends not only on the coordination geometry of the oxo-vanadium complex, but also on the kind of the substiuents on phenyl rings and bridge group. We found the electron withdrawing property decreases the electron density of the vanadium center by electron-withdrawing groups as strong I-acceptors through C=N bands while the J-donor property decreases or increases the electron density on the metal center via J- donation power of phenol oxygen.
