Accession Number:

ADA160034

Title:

The Role of Solvent Reorganization Dynamics in Electron-Transfer Processes. Theory-Experiment Comparisons for Electrochemical and Homogeneous Electron Exchange Involving Metallocene Redox Couples

Descriptive Note:

Technical rept.

Corporate Author:

PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY

Report Date:

1985-08-01

Pagination or Media Count:

38.0

Abstract:

Electrochemical Rate Constants and Activation Parameters are reported for the electron exchange of five metallocene couples and dibenzenechromium I O in eight solvents at mercury electrodes. The solvents acetonitrile, acetone, methylene chloride, formamide, N-methylformamide, N,N- dimethylformamide, dimethylsulfoxide, and benzonitrile were chosen so to provide substantial variations in their dynamical as well as dielectric properties. The metallocene couples are of the form MCp2o, where M Fe, Co, or Mn, and Cp cyclopentadiene or pentamethylcyclopentadiene. The inner- shell i.e., bond distortional barriers are calculated for the metallocene and arene couples from bond-distance and vibrational data to be small or approx, 0.25 kcalmol yet metal-dependent. Detailed comparisons of the observed solvent-dependent kinetics are made with the rate parameters calculated from contemporary theoretical treatments of outer-sphere electron transfer. Considerably better agreement between the experimental and theoretical kinetic parameters was obtained when the latter take into account the influence of solvent friction upon the barrier-crossing frequency. These results indicate that the conventional transition-state theory may not apply to electron-transfer reactions where the free-energy barrier is due chiefly to solvent reorganization, at least in high friction media where concerted solvent relaxation is slow.

Subject Categories:

  • Physical Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE