Solvent and structural effects on the electro- and photo-reduction of cis-β-[Co(trien)(RC6H4NH2)Cl]Cl2 type complexes in water/1,4-dioxane media

The electro- and photo-reduction of a series of cobalt(III) complexes of the type cis-beta-[Co(trien)(RC6H4NH2)Cl]Cl-2 where R=H, p-OMe, p-OEt, p-Me, p-Et, p-F and m-Me has been studied in 1,4-dioxane/water. The redox potential (E-1/2) and photo-reduction quantum yield (phi(Co(II))) data were correlated with solvent and structural parameters to shed light on the mechanism of these reactions. Correlation of E-1/2 and phi(Co(II)) with macroscopic solvent parameters viz. relative permittivity indicates that the reactivity is influenced by both specific and non-specific solute-solvent interactions. The Kamlet-Taft solvatochromic comparison method was used to separate and quantify these effects. Increasing the percentage of organic co-solvent in the medium enhances both reduction processes: there exists good correlation between E-1/2 and phi(Co(II)) suggesting a similar solvation in these redox processes.