Intervalence transfer in outer-sphere hexa-ammineruthenium(III) pentacyanoferrate(II) complexes

Abstract

The ion [Ru(NH₃)₆]³⁺ forms with substituted [Fe(CN)₅]^3– complexes a series of typical outer-sphere mixed-valence complexes, suitable for systematic studies on intervalence-transfer phenomena. The complexes of general formula [Ru(NH₃)₆][Fe(CN)₅L]·nH₂O (L = CO, CN, dimethyl sulphoxide, pyrazine, pyridine, or imidazole) exhibit typical intervalence bands in the visible spectra, with energies strongly dependent on the nature of the ligand L. The i.r. spectra of the complexes are consistent with the trapped-valence Ru^III, Fe^II formulation. A plot of optical electron-transfer energy against difference in the redox potential, ΔE^{[graphic ommitted]}, increases linearly with a slope of 1.39 ± 0.09 and an intercept of 108 ± 4 kJ mol^–1. The results are interpreted in terms of Hush's theory for intervalence transitions.