The Redox Chemistry of Manganese(III) and ‐(IV) Complexes

AbstractThe oxidation‐reduction thermodynamics for the manganese(III), ‐(IV), and ‐(II) ions, and their various complexes, are reviewed for both aqueous and aprotic media. In aqueous solutions the reduction potential for the manganese(III)/(II) couple has values that range from +1.51 V vs. NHE (hydrate at pH 0) to −0.95 V (glucarate complex at pH 13.5). The Mn(IV)/(III) couple has values that range from +1.0 V (solid MnIVO3 at pH 0) to −0.04 V (tris gluconate complex at pH 13.5). With anhydrous media the propensity for the Mn(III) ion to disproportionate to solid MnIVO2 and Mn(II) ion is avoided. For aprotic systems the range of redox potentials for various manganese complexes is from +2.01 V and +1.30 for the Mn(IV)/(III) and Mn(III)/(II) couples (bis terpyridyl tri‐N‐oxide complex in MeCN), respectively, to −0.96 V for the Mn(IV)/(III) couple (tris 3,5,‐di‐tert‐butylcatecholate complex in Me2SO). The redox reactions between manganese complexes and dioxygen species (O2, O2, and H2O2) also are reviewed.