Use of microelectrodes and spectroelectrochemical techniques in the study of redox properties of organometallic complexes: “Costa-type” coenzyme B 12 models

Abstract

The electrochemical behaviour of the “Costa-type” coenzyme B 12 model neopentyl- N 2, N 2'-propane-diylbis (2,3-butanedione-2-imine-3-oxime) Co(III) perchlorate complex has been studied using a platinum inlaid disk microelectrode techniques over a wide range of supporting electrolyte concentrations, and thin-layer absorption spectroelectrochemistry. In the former case, the separation of the two single electron transfers leading to Co(I) increased with decreasing supporting electrolyte concentration and, at the same concentration of the supporting electrolyte, with increasing radius of the cation. The likely explanation for this behaviour is the influence of ion-pair formation on the reduction potential of the redox couple involved in the second electron transfer that leads to a Co(I) complex bearing a negative charge. It has been demonstrated that the plot of the derivative of the steady-state current with respect to the electrode potential vs. E is morphologically identical to the derivative of the absorbance in thin-layer spectroelectrochemistry, and that the correlation between the results obtained using the two different techniques is useful for a better understanding of the electrochemical process.