Electrochemical reversibility of Me6Fc/Me6Fc+PF6- and Me8Fc/Me8Fc+PF6- redox systems in acetonitrile
Original scientific paper
Two new redox systems, sym. 1,2,4,1¢,2¢,4¢-hexamethylferrocene/cation sym. 1,2,4,1¢,2¢,4¢-hexamethylferricinium and sym. octamethylferrocene/cation sym. octamethylferricinium (MenFc/MenFc+, n = 6, 8) were studied by the cyclic voltammetry method. The observed difference between potentials of anodic and cathodic peaks of 0.063 to 0.075 V, and its independence on the potential scan rate, the straight-line dependence of the current value of anodic (and cathodic) peak on square root of the potential scan rate, as well as shapes of the recorded cyclic voltammograms indicate that both redox systems in acetonitrile meet the most important requirement of IUPAC regarding internal reference redox systems (IRRS) - electrochemical reversibility of electron transfer reaction. The same method under identical conditions was used to study the effect of the number of methyl groups on the redox potential of MenFc/MenFc+ systems, n = 0, 6, 8, 10. It was shown that the successive displacement of half-wave potential in the series of Fc/Fc+ -> Me6Fc/Me6Fc+ -> Me8Fc/Me8Fc+ -> Me10Fc/Me10Fc+ towards negative potentials is attributed to the electron-donor property of methyl groups. The location of the redox potentials values of new systems [n=6 (111 mV), n=8 (23 mV)] between redox potentials of systems of n = 0 (431 mV) and n = 10 (-77 mV) means that the redox potential of the systems of MenFc/MenFc+(n = 6, 8) has an optimal position on the electrode potential scale, i.e. meets another of the IUPAC criteria for IRRS.
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