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In aqueous acid, hydrazine reduces [MnIV3(μ-O)4(bipy)4(H2O)2]4+, (1), quantitatively to [MnIII,IV2(μ-O)2(bipy)4]3+, (2), and Mn2+ if [N2H+5] ≤ 2 × (stoichiometric amount). At higher [N2H+5], reduction proceeds up to Mn2+. The reduction of (1) to (2) is strongly catalysed by Mn2+ and the absorbance (At) versus time (t) graphs have sigmoidal shapes. The graphs become steeper with increasing amounts of added Mn2+ and N2H+5, but remain unchanged when [H+] is changed. The At − t graphs, under various experimental conditions, can all be simulated with a single set of second order rate constants, estimated for the individual steps in a proposed reaction scheme, in which the catalytic action of Mn2+ involves a one-electron and a two-electron reduced form of (1), but not (1) itself. The absence of any proton-dependence of the reaction rate refutes an electroprotic mechanism and an inner-sphere mechanism appears to be most likely for the reduction of (1) by N2H+5 |
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