Pulse-radiolytic investigation of the oxidation of iron(II) and iron(III) complexes with 2,2′-bipyridine

Abstract

The absorption spectra and decay kinetics of intermediates formed by the reaction of tris(2,2′-bipyridine) complexes of FeII and FeIII with H atoms and OH radicals have been studied in aqueous solution using the pulse radiolysis technique. The product of the oxidation of [Fe(bipy)3]2+ with H atoms in acid solution is an [Fe(bipy)3H]2+ hydride intermediate which decomposes to give hydrogen and [Fe(bipy)3]3+. Intermediates formed by addition of OH to [Fe(bipy)3]2+ have complex kinetics probably indicating that a mixture of isomers is formed in the process. These OH adducts do not oxidize water to oxygen even in the presence of a catalyst such as colloidal RuO2, Mn2+, Co2+, or Ni2+. The OH adduct of [Fe(bipy)3]3+ also does not react with water to produce oxygen. Oxygen can be produced in stoicheiometric amounts by reaction of Br2– with [Fe(bipy)3]2+ catalyzed with RuO2. The absorption spectra of OH adducts of [Fe(bipy)3]3+ and the kinetics of their reactions are reported and discussed.