Electrochemical Investigation of Redox Processes of Labile Cu(II)/Cu(I)-Cl Complexes by Scanning Electrochemical Microscopy.

The studies reported here provide detailed information on the kinetics and reaction mechanism determined by the scanning electrochemical microscopy (SECM) for Cu(II)/Cu(I) redox reactions in a system with excess chloride. In positive feedback mode, the tip voltammograms obtained consist of two partially overlapping reduction waves, not one quasi-reversible process as was always thought. The reduced species of CuIICl42- and [CuIICl3(H2O)]- could coexist during the time scale of SECM measurements, due to the slowness of the ligand substitution reaction of [CuIICl3(H2O)]- to CuIICl42-. The stepwise EC reactions of CuIICl42- have experienced the same electron transfer kinetics as do outer-sphere reactants, while the reactions of [CuIICl3(H2O)]- followed concerted EC pathways and much lower rate constants can be obtained, mainly due to the nonadiabatic character of electron transfer (k0Pt/k0Au = 1.625). The findings of this study can offer valuable insights for analyzing the electrode kinetics of labile complexes of metals in aqueous solutions.