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

Abstract

Department of Chemistry, University of Allahabad, Allahabad-211 002, Uttar Pradesh, India E-mail : [email protected] Manuscript received 14 November 2007, revised 2 September 2008, accepted 10 September 2008 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 PI-working electrode. The electrochemistry of sal-anl 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_pa1 = -0.90 V and E_pa2 = -1.325 V vs SCE followed by an irreversible anodic peak at E_pa'2 = -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 a₁ and c₂ are metal-based while the redox processes a₂ 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 VO^2+/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•