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 Fe^II and Fe^III 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.