G. Desantis et al., CONTROLLING THE ACIDITY OF THE CARBOXYLIC GROUP BY A FERROCENE BASED REDOX SWITCH, Inorganica Chimica Acta, 225(1-2), 1994, pp. 239-244
The pH dependent oxidation behaviour of the ferrocene subunit in ferro
cenylcarboxylic acids of formula Fc(CH,),COOH (n=0, 1, 2) has been inv
estigated through differential pulse voltammetry experiments in 4:1 ac
etonitrile/water solutions. Different voltammetric responses have been
obtained depending whether the pH has been varied through a buffer (a
single peak, whose E(1/2) value decreases with the increasing pH) or
through an acid-base titration (two distinct peaks, the less anodic co
rresponding to the oxidation of the FcCOO(-) species, the more anodic
corresponding to the oxidation of the FcCOOH species, whose relative i
ntensities vary with the pH). The electrochemically determined pK(a) v
alues for the Fc(CH2)(n)COOH and [Fc(+)](CH2)(n)COOH forms indicate th
at the Fc-to-Fc(+) oxidation process makes the acidity of the proximat
e carboxylic group increase. Such a switching effect, electrostatic in
nature, decreases as n increases.