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

Abstract The 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 Mn IV O 3 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 Mn IV O 2 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 Me 2 SO). The redox reactions between manganese complexes and dioxygen species (O 2 , O 2 , and H 2 O 2 ) also are reviewed.