Electrochemical investigations of oxovanadium(IV) complexes with bidentate Schiff base ligands in dimethylformamide

The electrochemical redox properties of bidentate Schiff base oxovanadium(IV) complexes viz. VO(sal-anl)(2) 1, VO(sal-tod)(2) 2, VO(hmp-and)(2) 3 and VO(hmp-oxime)(2) 4 have been studied In DMF/0.1 M TBAP using cyclic voltammetry at a Pt-working electrode. The electrochemistry of sal-ani and sal-tod ligands was also examined for the sake of comparison. Complexes 1 and 2 show almost similar electrochemistry. Oxidation of complex 2 is easier while reduction is difficult in comparison to 1 due to the +I inductive effect of electron-donating methyl group at the para position of toluidine. Complex 1 showed two irreversible anodic waves at E-pa1 = +0.68 V and E-pa2 = + 1.06 V vs SCE and two irreversible cathodic peaks at E-pc1 -0.90 V and E-pc2 = -1.325 V vs SCE followed by an irreversible anodic peak at E-pa2 = -0.42 V at scan rate 100 mV s(-1). On the basis of CV results, it is concluded that in complexes 1 and 2, the redox processes a(1) and c(2) are metal-based while the redox processes a(2) and c(1), seem to be ligand-based. The CVs of 3 and 4 are also qualitatively similar. It is noteworthy that the anodic peak potential for the process VO2+/3+ shifted to more positive values in the sequence : VO(sal-tod)(2) -> VO(sal-anl)(2) -> VO(hmp-oxime)(2) -> VO(hmp-and)(2).