AN ELECTROANALYTICAL INVESTIGATION ON THE REDUCTION OF HIGH-SPIN OCTAHEDRAL COMPLEXES OF NICKEL(II) WITH SCHIFF-BASE LIGANDS

The electrochemical reduction of a series of high-spin octahedral complexes of nickel(II) with a variety of Schiff base ligands of the type R-N = CH-Py (Py = pyridyl; R = CH3; C6H5; o-, m- or p-CH3-C6H4; o-, m- or p-Cl-C6H4; o-, m- or p-CH3O-C6H4) has been investigated in acetonitrile. All these complexes undergo a fairly reversible two-electron reduction process in which the parent hexacoordinate nickel(0) species is initially formed. This primary electrode product decomposes quickly in the homogeneous phase leading to the release of free ligands and to the formation of a tetracoordinate nickel(0) complex which is in turn of fairly low stability. The kinetic constant of the chemical decay following the charge transfer step has been determined for all the complexes investigated by the cyclic voltammetric approach. The dependence of the obtained kinetic constant values on the nature of the ligands present in the coordination shell is discussed together with the effect of these ligands on peak potential values. Also the circumstance under which all the nickel(II) complexes investigated are not reduced in steps to nickel(0) but undergo a direct two-electron uptake is considered by taking into account their high-spin configuration.