Voltammetric behaviour of transition metal complexes with extended - systems schiff base ligands: N,N′-ethylenebis(acetylacetoniminato)palladium(II), copper(II) and nickel(II) complexes

Abstract

The redox properties of complexes of Pd(II), Cu(II) and Ni(II) with the N,N′-ethylenebis(acetylacetoniminate) ligand, [(acac) 2en] 2−, have been investigated by cyclic voltammetry, chronoamperometry and controlled potential coulometry in acetonitrile solvent at platinum and mercury electrodes. The one-electron oxidation product of [Pd{(acac) 2en}] has been identified as the dimeric cation [Pd{(acac) 2en}] 2 2+; the cathodic reduction of the starting complex originates the corresponding Pd 1 species, stable only in the voltammetric time-scale. The electrooxidation process of [Cu{(acac) 2en}] leads to the short-lived corresponding [CuL] + species, from which free Cu + or Cu 2+ ions generate, depending on the working potential; the overall cathodic process appears to be rather complicated. The [Ni{(acac) 2en}] complex undergoes an irreversible one-electron oxidation in the voltammetric time-scale, while the overall anodic process gives rise to a doubly charged cationic species, from which the parent compound can be electrolytically regenerated. Comparisons with the previously reported voltammetric properties of N,N′-ethylenebis(monothioacetylacetoniminato) metal complexes have been done; the effect on E 1 2 values of substitution of oxygen for sulphur in the atom donor set is outlined.