THIN-LAYER SPECTROELECTROCHEMICAL STUDIES OF COBALT AND COPPER SCHIFF-BASE COMPLEXES

A series of 19 cobalt and copper Schiff base complexes has been studied in N, N-dimethylformamide by thinlayer electro and spectroelectrochemistry employing a gold minigrid optically transparent thin-layer electrode. The cobalt complexes exhibit Nernstian reversibility for both Co(II)/Co(III) and Co(I)/Co(II) couples, even though many exhibit only quasi-reversible behavior when studied by conventional bulk solution cyclic voltammetry. For closely related cobalt complexes there is a qualitative correlation between E0/ for cobalt(II) reduction andthe energy of the metal-to-ligand charge-transfer band of the cobalt(I) complex. E°ʹ for the Co(II)/Co(III) couple is relatively insensitive to the structure of the equatorial ligand. E°ʹ for the Co(I)/Co(II) couple is markedly dependent upon the degree of unsaturation in the equatorial Schiff base, greater unsaturation stabilizing thecobalt(I) form. The copper complexes also show Nernstian reversibility for the Cu(I)/Cu(II) couple under thin-layer conditions. The copper(I) complexes are stabilized by ligand unsaturation to the same extent as are the cobalt(I) analogues. Reduction of Cu(II) complexes generally occurs more easily than reduction of the analogous Co(II) complexes. Values of E°ʹ for the Cu(I)/Cu(II) and Co(I)/Co(II) couples, as ligand structures are varied, are linearly related to each other, implying that the effects of equatorial ligand structure variation on Eof valuesare coherent and therefore predictable from one system to the next. This work demonstrates the efficacy and utility of thin-layer spectroelectrochemical methodology in a nonaqueous inorganic redox system. © 1979, American Chemical Society. All rights reserved.