Variation of electrode potential and charge transfer bands in series of tetravalent ruthenium complexes [RuCl 6 - n (PrCN) n ] n - 2

Abstract

A truncated series of ruthenium(IV) complexes [RuCl(6 - n )(RCN)n]n - 2 (n = 0-3; R = n-propyl) has been electrogenerated in situ and characterized spectroscopically. This substitution series allowed the examination of the variation of electrode potential of Ru+4/Ru+3 couple and the accompanying trends in ligand-to-metal charge-transfer (LMCT) spectra. The Cl → Ru4+ charge transfer manifold red-shifted from n = 0-2, and then moved back to the blue edge upon the third substitution of chloride with nitrile. Moreover, the anodic shift in Ru+4/Ru+3 redox couple upon the third chloride replacement was barely half the expected change. These irregular trends contradict the results of the DFT studies and the tenet of ligand additivity principle.