Oxidation of the thiosulfate ion with a (µ-oxo)diiron(III) complex: kinetic evidence for self reaction of the thiosulfate radical ion
Abstract
In aqueous Hphen+–phen buffer media (pH 3.9–5.2), the complex ion [FeIII2(µ-O)(phen)4(H2O)2]4+ 1 (phen = 1,10-phenanthroline) has been shown to oxidise the thiosulfate ion to the tetrathionate ion. In the presence of excess phenanthroline, 1 itself was reduced to [Fe(phen)3]2+ 32+, an inhibitor for the reaction. According to the proposed mechanism, an inner-sphere, one-electron reduction of 1 by S2O32– generates [Fe(phen)3]3+ 33+, [Fe(phen)3]2+ 32+ and the thiosulfate radical ion S2O3–; 33+ is then further reduced to 32+ by another S2O32– ion. The radical ion S2O3– either re-oxidises 32+ to 33+ and thus inhibits the reaction, or produces the tetrathionate ion through a self reaction. Kinetic activity of 1 swamps that for its hydrolysed derivatives.