Fe(II)+Fe(III) exchange reaction in concentrated perchloric acid solutions

Abstract

The electron exchange rate between Fe(II) and Fe(III) is k[Fe(II)][Fe(III)] for solutions containing 1–7 M HClO₄ in the temperature range 0 to –84°C. k at 0.3°C shows an unexpected dependence on [HClO₄] but for [HClO₄]= 7.5 M, ΔS^≠= 13.2±1.0 cal deg.^–1 mole^–1 and ΔE^≠= 11.0±0.4 kcal mole^–1 over the whole temperature range notwithstanding the facts (a) that the system changes from a liquid to a glass at –56°C and (b) that the specific conductivity shows a discontinuity in Arrhenius parameters at this temperature. It is suggested that electron exchange can occur over long distances in this medium.