Mechanistic studies on the intra-molecular electron transfer in the adduct species of some oxo-centred trinuclear iron(III)/chromium(III) cations and l-ascorbic acid in aqueous acetate buffer

The kinetics of the intra-molecular electron transfer of the adduct of l-ascorbic acid and a series of mixed metal Cr2Fe oxo-centred trinulear complexes, of the general formula [Cr2Fe(μ3-O)(μ2-RCO2)6(H2O)3]+ (where R = H, CH3, CH3CH2 and (CH3)2CH) were investigated spectrophotometrically, in aqueous carboxylate buffer. The reactions were studied over the ranges 2.34 ⩽ pH ⩽ 4.45, 25.0 ⩽ θ ⩽ 35.0 °C at an ionic strength of 0.50 mol dm−3 (NaClO4). The reaction involves an equilibrium step between both triaqua and diaquahydroxo species of the complex cations and l-ascorbic acid, resulting in the formation of an adduct. These equilibrium steps are followed by a slower one-electron oxidation step, corresponding to the reduction of the iron(III) centre(s) which is proceeded by rapid decomposition of the oxo-centred trinuclear core to yield aqueous iron(II), and dinuclear chromium(III). The dinuclear chromium(III) further decomposes by aquation to give an aqueous solution of the metal ions and free ligands.