TY - JOUR
T1 - Electrochemical and homogeneous exchange kinetics for transition-metal aquo couples
T2 - Anomalous behavior of hexaaquoiron(III/II)
AU - Hupp, Joseph T
AU - Weaver, Michael J.
PY - 1983
Y1 - 1983
N2 - 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.
AB - 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.
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M3 - Article
AN - SCOPUS:33845550253
VL - 22
SP - 2557
EP - 2564
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 18
ER -