Synthesis, spectral characterization and solvent H-bonding effects on the electro and photo-reduction of mixed ligand cobalt(III) complexes

Department of Chemistry, Gandhi gram Rural Institute-Deemed University, Gandhigram-624 302,

Tamilnadu, India

E-mail : drkpelango@rediffmail.com

Manuscript received 31 January 2011, revised 07 June 2011, accepted 20 June 2011

Seven new Co^III complexes of the type cis-β-(Co(dmen)₂(R-aniline)CI]CI₂ where dmen = N,N'-dimethylethylenediamine, R = p-H, p-F, p-Me, p-Et, p-OMe, p-OEt and m-Me have been synthesized and characterized by elemental analysis, UV-Vis, FT-IR, ¹H NMR, TGA and differential pulse voltammetric (DPV) techniques. Further, the electro and photo-reduction of these Co^III complexes has been studied in propan-2-ol/water and 1,4-dioxane/water binary mixtures. The redox potential (E_1/2) and the photo-reduction quantum yield (Φ_C0^II ) data were correlated with solvent and structural parameters with an aim to shed some light on the mechanism of these reactions. Correlation of E_1/2 and Φ_Co^II with solvent parameters indicated that the reactivity is influenced by both specific and non-specific solute-solvent interactions. The electro- and photo-reduction of these complexes was observed to become increasingly easier with an increase in the dipolarity/polarizability of the medium as evidenced by the Kamlet-Taft correlation. The difference in the relative easiness of the reduction has been explained using the difference in H-bonding properties of the co-solvents.