ELECTROCHEMISTRY OF [V(III)EDTA](-) IN ETHYLENE GLYCOL-WATER MIXTURES.2. KINETIC ASPECTS - SOLVATION OF THE TRANSITION-STATE

The effect of the solvent composition for water-ethylene glycol (EG) m ixtures in the mole fraction range X(EG) = 0-1 on the kinetics of the lenediamine-N,N,N',N'-tetraacetatovanadate(III/II) redox reaction has been investigated at a mercury electrode using convolution potential s weep voltammetry. Capacitance data for the mercury/solvent mixture int erface have been obtained at two different concentrations of NaClO4 at each solvent composition. Observed electron transfer rates and transf er coefficients have been corrected for double-layer effects using the se data. It has been shown that the change of the corrected electron t ransfer rates with solvent composition is due to differences in the so lvation of the complex and can be described by a two-step solvent exch ange mechanism. In addition, Gibbs energies of reorganization have bee n estimated using the experimental results. The logarithm of the corre cted electron transfer rate constant also corrected for variation in t he outer sphere contribution to the Gibbs reorganization energy is lin early correlated to the logarithm of the solvent's longitudinal relaxa tion time (tau(L)) The solvent composition of the solvation shell of t he transition state can be calculated from the estimated values of tau (L) in each mixture. As expected, the composition of the solvation she ll of the activated complex is intermediate between that of the reacta nt and product.