ELECTRON-TRANSFER KINETICS OF SELF-ASSEMBLED FERROCENE OCTANETHIOL MONOLAYERS ON GOLD AND SILVER ELECTRODES FROM 115-K TO 170-K

The electron-transfer kinetics of CpFeCp(CH2)(8)SH and of CpFeCpCO(2)( CH2)(8)SH monolayers cochemisorbed with n-octanethiol diluent on gold and silver electrodes have been measured in chlororethane/butyronitril e solvent over temperatures of 115-170 K by cyclic voltammetry and pot ential step experiments. Rate constants for CpFeCpCO(2)(CH2)(8)SH mono layers are smaller than those for CpFeCp(CH2)(8)SH monolayers by a fac tor approximately equivalent to insertion of two -CH2- groups. Activat ion plots of rate constants k(0) for CpFeCp(CH2)(8)SH and for CpFeCpCO (2)(CH2)(8)SH monolayers on gold give reorganization energies (lambda) of about 0.95 eV which is similar to 0.2 eV larger than predicted fro m dielectric continuum theory. Broadened voltammetric peaks and curved potential step ln(i) vs time plots indicate a kinetic inhomogeneity a mong the surface ferrocene population; the effects of this inhomogenei ty appear to cause artificially small values of reorganization energie s (0.02-0.34 eV) when cyclic voltammetric wave shapes and log(k(APP)) vs eta plots are analyzed for lambda. Preliminary results for rate con stants k(0) for CpFeCp(CH2)(8)SH monolayers on Ag are similar to those on Au but with a smaller barrier energy.