Mechanism of photoinduced redox reactions in aqueous solutions of [Fe(bpy)(CN) 4] 2−

Abstract

The mechanism of redox reactions initiated by UV excitation of [Fe(bpy)(CN) 4] 2− in aqueous solutions has been investigated by continuous photolysis, laser kinetic spectroscopy and pulse radiolysis. Hydrated electrons formed in the light induced reaction are shown to react with ground state [Fe(bpy)(CN) 4] 2− to form [Fe(bpy)(CN) 4] 3− characterized by its absorption spectra and reactions. The back reaction between [Fe(bpy)(CN) 4] − and [Fe(bpy)(CN) 4] 3− takes place with kl.8±4x10 10 M −1 s −1. The quantum yield of solvated electron formation determined by using nitrate ions as electron scavenger is 0.14±0.01 and 0.068±0.007 at μ∼ 0.01 and μ∼ 1.0, respectively. Addition of methylviologen (MV 2+) to the solution of iron(II) complex leads to production of MV+ via direct electron scavenging and an electron transfer reaction from [Fe(bpy)(CN) 4] 3−. The latter process takes place with k = 9.0±0.6 x 10 9 M −1 s −1. The decay of MV + occurs in reactions with both iron(III) and iron(II) complexes.