Jn. Richardson et al., ELECTRON-TRANSFER KINETICS OF SELF-ASSEMBLED FERROCENE (C12)ALKANETHIOL MONOLAYERS ON GOLD ELECTRODES FROM 125K TO 175K, Electrochimica acta, 40(10), 1995, pp. 1331-1338
The electron transfer kinetics of monolayers of CpFeCpCO(2)(CH2)(12)SH
and CH3(CH2)(11)SH co-chemisorbed on gold electrodes have been measur
ed in 2:1 (v:v) chloroethane/butyronitrile solvent at temperatures ran
ging from 125K to 175K with potential steps and cyclic voltammetry. Ra
te constants, k degrees, measured using cyclic voltammetry range from
3 x 10(-4) to 10(-1) s(-1) over these temperatures; an:activation plot
of log[k degrees/k(b) T-1/2] vs. 1/T gave lambda = 0.89 eV for the re
organization energy for the Cp(2)Fe(+/0) reaction and a pre-factor of
6.5 x 10(6) eV(-1+s-1). The rate constants were obtained by comparison
of experimental Delta E(PEAK) values with those of cyclic voltammogra
ms digitally simulated with Marcus-DOS theory. A value of lambda = 0.7
6 eV is predicted from dielectric continuum theory. The CpFeCpCO(2)(CH
2)(12)SH monolayers are kinetically inhomogeneous (disperse) as shown
by non-linear In[i] vs. time plots in potential step experiments. The
kinetic dispersity has adverse effects on determinations of lambda val
ues from cyclic voltammetric waveshapes and from plots of potential st
ep-derived rate constants, k(app,eta,,) against overpotential (eta), p
roducing depressed values for lambda.