The use of free energy relationships to rationalise structural and solvent effects on the photoreduction of cobalt(III) complexes in aqueous organic solvent medium

Quantum yields for the photoreduction of a series of Co^III complex ions, [CoClen₂ (RC₆H₄NH₂)]²⁺ where R=p-OMe, p-OEt, p-Me, m-Me, H and p-F using a low pressure Hg vapour lamp (254 nm) in aqueous ethanol mixtures (15–40% v/v organic cosolvent), increase with increase in mole fraction of the cosolvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the quantum yield data with Kamlet–Taft's solvatochromic parameters indicates that the specific solvent–solute interactions play a dominant role in governing the reactivity.