MECHANISM OF OXIDATION OF IRON(II) COMPLEXES BY THE AZIDE RADICAL

The reactions of azide radicals (N-3(.)) with both iron(II) aquo- and iron(II) azide complexes have been investigated using pulse radiolysis , the second-order rate constants for the reactions being measured as (3.2 +/- 1.0) x 10(6) and (5.2 +/- 0.5) x 10(8) dm(3) mol(-1) s(-1), r espectively. From the transient spectra, it was proposed that the imme diate product of the reaction of N-3(.) with iron(II) azide complexes was a novel iron(II)-complexed azide radical (Fe2+N3.)(aq) having a ch aracteristic optical absorption at 300 nm and 410 nm (epsilon = 1700 a nd 1100 dm(3) mol(-1) cm(-1), respectively). From the effect of both p H and azide ion concentration on the kinetic fate of (Fe2+N3.)(aq), it is proposed that intramolecular electron transfer occurs for both (Fe 2+N3.)(aq) and its deprotonated form, [(Fe2+N3.)(OH-)](aq), with first -order rate constants of (1.2 +/- 0.3) x 10(4) and (5.4 +/- 0.4) x 10( 4) s(-1), respectively. At relatively high azide concentrations (> 10( -3) mol dm(-3)), the observable product of these reactions is the iron (III) species, [Fe3+(OH-)(N-3(-))](aq), whereas at lower azide concent rations, the hydroxo product, Fe3+(OH-)(aq), is observed.