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

Abstract

The electro- and photo-reduction of a series of cobalt(III) complexes of the type cis-β-[Co(trien)(RC₆H₄NH₂)Cl]Cl₂ 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 (φ_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 φ_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 φ_Co(II) suggesting a similar solvation in these redox processes.

Keywords:

• Cobalt(III) complexes
• Photo-reduction
• Electrochemistry
• Solvent effect
• Hammett equation

Acknowledgements

We are grateful to the University Grants Commission, New Delhi, for financial support of this research. Also, the authors thank Dr. S. Abraham John, Lecturer in Chemistry, Gandhigram Rural University, Gandhigram, for providing CV instrument and for the scientific discussions during the preparation of the manuscript.