Oxidation of ferrocenes by copper(II) in aqueous acetonitrile: nitrate and chloride ion effects

The effect of nitrate and chloride ion on the rate of oxidation of ferrocene (Fc) and 1,1'-dimethylferrocene (DmFc) by Cu(II) has been studied in 95% and 80% acetonitrile/water solutions. The complex formation constants for Cu(II) with the same anions in the same media have been determined by spectrophotometry. Nitrate ion mildly inhibits the reaction, while chloride ion substantially increases the rate. The results have been analyzed in terms of the Marcus theory, and it is concluded that complexation increases the rate of self-exchange between the CuII(X)n and CuI(X)n species. In the case of nitrate, the latter effect is compensated for by a less favorable overall equilibrium constant, which results in mild inhibition.

“Abnormal” Salt and Solvent Effects on Anion/Cation Electron-Transfer Reactions: An Interpretation Based on Marcus−Hush Treatment

Salt and solvent effects on the kinetics of the reactions [Fe(CN)6]3- + [Ru(NH3)5pz](2+) right arrow over left arrow [Fe(CN)6]4- + [Ru(NH3)5pz]3+ (pz = pyrazine) have been studied through T-jump measurements. The forward and reverse reactions show different behaviors: "abnormal" salt and solvent effects in the first case and normal effects in the second one. These facts imply an asymmetric behavior of anion/cation reactions depending on the charge of the oxidant. The results can be rationalized by using the Marcus-Hush treatment for electron-transfer reactions.