Anomaly of double-decker bis(phthalocyaninato)cerium(IV) in its electrochemical properties amongst rare-earth analogs

Abstract

Redox properties of the title complex [ Ce ( pc )2] (where pc denotes phthalocyaninate dianion, C 32 H 16 N 82-) have been investigated in dichloromethane solutions by cyclic- and rotating-disk-electrode voltammetry. Unlike the other rare-earth(III) analogs that show one oxidation and one reduction waves in the potential range of -1 – +1 V vs. the half-wave potential of the redox couple of ferrocene (Fc+/Fc), only the cerium(IV) derivative shows two oxidation and one reduction waves in the same potential range. The first and second oxidation and the first reduction waves have been assigned as pc2-pc•-/pc2-pc2-, pc•-pc•-/pc2-pc•-, and Ce IV / III ( pc 2-)2, respectively, on the basis of spectroelectrochemical works. The ligand-centered electron-transfer processes are fully reversible and diffusion-controlled whereas the first reduction alone is quasi-reversible. Comparison of absorption and magnetic circular dichroism spectra before and after the metal-centered reduction suggests that structural change upon the electron-transfer is not significant in solution apart from the interplanar distance between the two macrocyclic ligands.