Rate data for electrochemical and homogeneous redox reactions involving Ruaq 3+/2+, Vaq 3+/2+, Feaq 3+/2+, Euaq 3+/2+, and Craq 3+/2+ redox couples (where "aq" represents aquo ligands) have been analyzed and compared by using the rate relations due to Marcus in order to ascertain how the kinetics of outer-sphere electron exchange are dependent upon the metal redox center. The work-corrected rate constants for electrochemical exchange at mercury electrodes, ke ex, were found to be in uniformly good agreement with the rate constants for homogeneous self-exchange, kh ex, extracted from cross-reaction data involving outer-sphere coreactants, yielding the reactivity sequence Ruaq 3+/2+ > Vaq 3+/2+ > Feaq 3+/2+ ≳ Euaq 3+/2+ ≳ Craq 3+/2+. However, the measured rate constant for Feaq 3+/2+ self-exchange is not consistent with this sequence, being at least 103-fold larger than the values of kh ex extracted from both the homogeneous cross-reaction and electrochemical data. The latter values of kh ex and also ke ex are in harmony with the relative inner-shell barriers for Feaq 3+/2+ and Ruaq 3+/2+ calculated from crystallographic structural data. The above reactivity sequence is also consistent with the relative structural changes accompanying electron transfer as monitored by the corresponding reaction entropies.
|Number of pages||8|
|Publication status||Published - 1983|
ASJC Scopus subject areas
- Inorganic Chemistry