Medium effects on the electron-transfer processes: Reduction of aquapentaamminecobalt(III) by hexacyanoferrate(II) in ethyleneglycol-water, ethylene carbonate-water and urea-water media

Abstract

824-831The outer-sphere electron transfer between Co(NH3)5OH and Fe(CN) - which proceeds via precursor ion-pair formation has been investigated in ethylene glycol-water (0-47.6 wt% of EG), ethylene carbonate-water (0-40 wt% of EC) at 20-35ᵒC and in urea-water (0-19.4 wt% of EG) at 25ᵒC (I = 0.50 mol dm-3 NaNO3)· The electron transfer rate constant for the ion pair (k, s-1) follows the order H2O ~ U-H2O 2O 2O. The specific solvent effect on the rate constant for EGH2O and EC-H2O media can be account d for in the frame work of the Marcus theory by considering the ion solvent dipole interaction in the solvent cospheres of the precursor and the successor ionpairs. Both H≠ and S≠ decrease linearly with increase in mole fraction of EC(XEC) while for the EG-H2O media a broad maximum s discernible in the plot of H≠ (or S≠)­ versus XEG indicating thereby that the solvent structural effects might mediate the activation process