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The electron transfer kinetics of monolayers of CpFeCpC0 2 (CH 2 ) 12 SH and CH 3 (CH 2 ) U SH co-chemisorbed on gold electrodes have been measured in 2:1 (v:v) chloroethane/butyronitrile solvent at temperatures ranging from 125K to 175K with potential steps and cyclic voltammetry. Rate constants, k°, measured using cyclic voltammetry range from 3x10"* to 10" 1 s" 1 over these temperatures; an activation plot of logtkVkbT*] vs. 1/T gave k = 0.89 eV for the reorganization energy for the Cp 2 Fe +/0 reaction and a pre-factor of 6.5xl0 6 eVV 1 . The rate constants were obtained by comparison of experimental AE PEAK values with those of cyclic voltammograms digitally simulated with Marcus-DOS theory. A value of X = 0.76 eV is predicted from dielectric continuum theory.The CpFeCpC0 2 (CH 2 ) 12 SH monolayers are kinetically inhomogeneous (disperse) as shown by non-linear ln[i] vs. time plots in potential step experiments. The kinetic dispersity has adverse effects on determinations of X values from cyclic voltammetric waveshapes and from plots of potential step-derived rate constants, k.^^ against overpotential (??), producing depressed values for X.

Wo ropad cy& vokmmtryfrom 115 to 180 Kln butyronltrlk/ ethyl chlodde solvent for monolayer films of ferrocenetormlnatod alkanothlds chemkorbod on gold electrode rurfacos. The alkyl spacers botweon thlol and ferrocene contalnod 4, 8, and 12 methylene unlts, and the forrocene m0ktko wero diluted wlth alkanethldr of qual chaln length durlng Un-aumnbly of the monomokcular f h onto the gdd electrodw. The -If-a8wnM.d forrocone flbnr dkplay hlghly stabh voltammetry at low temperatures. The magnttudes of tho voltammetrlc peak potontlal soparatlons (AEW) are domlnatod by slow electron-tramfor klnetlcr as opposed to uncompensated rdutlon redstance. Qualltathrely, the electrorctramfor rat08 decrease wlth decreadng temperaturo and wtth Incroadng alkyl chain kngth. The ferrocone alkanethlok retaln m o degree of order and enforcement of a spaclng botween tho electrode and tho ferrocone &ea In splto of their

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Fluid electrolyte solutions based on mixtures of butyronitrile (PrCN) and ethyl chloride (EtCl) with Bu4NPF6 or Bu4NClO4 as electrolyte freeze below −180°C and provide excellent media for cryogenic electrochemical experiments. A 1:2 mixture of PrCN and EtCl exhibits the best combination of freezing point and ionic conductivity for ultralow temperature electrochemistry. Diffusion coefficients for bis(pentamethylcyclopentadienyl) iron false(Cp2*normalFefalse) are measurable by potential step chronoamperometry down to −160°C using a conventionally sized electrode, but the resistivity of the solvent mixture is such that potential sweep voltammetry benefits from the use of microdisk (10 and 25 μm diam Pt) or microband (0.2 μm wide Au) electrodes. Voltammetry at a chemically modified electrode down to −170°C is presented for the case of thin films of normalpoly‐false[normalOsfalse(normalbpy)2false(normalvpy)2false]false[PF6]2 .