Variation of electrode potential and charge transfer bands in series of tetravalent ruthenium complexes [RuCl6−n(PrCN)n]n−2

•The LMCT band shifted bathochromically from n = 0–2, and then moved back to the blue edge on third Cl substitution.•DFT/B3LYP calculations on halide donor and RuIV acceptor levels are inconsistent with observations.•The anodic shift in Ru+4/Ru+3 redox couple on the third Cl replacement was barely half the expected change.•The calculated frontier orbital energies tend to support the trend in redox potential.

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.

Graphical abstractA 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. 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. The irregular trends contradict the results of the DFT studies and the tenet of ligand additivity principle.Figure optionsDownload full-size imageDownload as PowerPoint slide