HETEROGENEOUS ELECTRON-TRANSFER DYNAMICS OF DECAMETHYLFERROCENE FROM 130-K TO 181-K

Kinetic parameters for heterogeneous electron transfer are reported fo r decamethylferrocene in two low-temperature solvent systems: butyroni trile and 2:1 (v:v) ethyl chloride/butyronitrile, The(Me(5)C(5))(2)Fe- +/0 rate constant ranges from 4 x 10(-6) to 10(-3) cm/s over the tempe ratures investigated. Temperature-dependent heterogeneous electron-tra nsfer rate constants used for the determination of activation paramete rs were obtained from comparison of experimental cyclic voltammograms to those produced via digital simulation employing Marcus-DOS kinetic theory. The activation parameters are similar in the two solvents (Del ta G = 0.27 and 0.26 eV) and are somewhat larger than predicted for a n outer-sphere reorganizational barrier from dielectric continuum theo ry (Delta G = 0.22 and 0.21 eV). Available literature values for the inner sphere barrier for (Me(5)C(5))(2)Fe-+/0 and the thermal activati on of solvent dipole longitudinal relaxation times are compatible with the experimental barriers containing small contributions from these s ources. This work represents the lowest temperature electrochemical ki netic study to date employing a diffusing redox species in liquid solu tion.