Kinetics of oxidation of nitrogen(III) by an oxo-bridged dinuclear manganese(III,IV) complex in weakly acidic media
Abstract
The heterovalent oxo-bridged dinuclear manganese(III,IV) complex [Mn2O2(phen)4]3+1 aquates to [Mn2O2(phen)3(H2O)2]3+2(phen = 1,10-phenanthroline) in phen–Hphen+ buffer (pH 4–5). The equilibrium constant for the reaction was kinetically evaluated as K1H= 35 ± 10. Nitrite ion formed adducts 1N and 2N with 1 and 2 respectively. Their respective association constants, K1N= 14.1 ± 2 dm3 mol–1 and K2N= 50 ± 10 dm3 mol–1, are small and indicate the outer-sphere nature of the adducts. Adduct 2N is reduced via one-electron steps, ultimately to MnII with a rate constant k2N=(3.33 ± 0.6)× 10–2 s–1 at 30.0 °C and I= 0.10 mol dm–3 for the first step. No kinetic activity of 1N was detectable under the experimental condition employed. Added Mn2+ has been found to scavenge phen from the reaction media and thus promotes the formation of 2N and hence the reaction rate.