Pentacyanoferrate(II) complexes: evaluation of their formal potentials and mechanism of their quenching of tris(2,2'-bipyridine)ruthenium(II) luminescence

Abstract

Formal reduction potentials (E/sup 0/') for complexes of the pentacyanoferrate ion with a number of unsaturated ligands have been measured by cyclic voltammetry and potentiometry. From the association constants for the complexes in the iron(II) form (K/sub II/) and the E/sup 0/' values, the corresponding constants for the iron(III) complexes (K/sub III/) have been calculated. The K/sub III/ values are found to increase with the basicity of the ligand, while the opposite trend is found for the K/sub II/ values. These opposing trends are discussed in terms of the bonding properties of the pentacyanoferrate ion. The quenching of the luminescence of the excited state of tris(2,2'-bipyridine)ruthenium(II) by pentacyanoferrate(II) complexes has also been investigated. For most of the complexes, including several previously reported hexacyanometalates, the quenching rate constants parallel their reduction potentials as is expected for a quenching mechanism involving reduction of the ruthenium excited state by iron(II).