Abstract
Suitable theoretical formalisms are outlined for examining and predicting rate parameters for outer-sphere electron transfer in heterogeneous and homogeneous environments on a unified basis. They are utilized to calculate rate constants and activation parameters for 11 electrochemical and 45 homogeneous self-exchange and cross reactions involving transition-metal aquo, ammine, ethylenediamine, and polypyridine redox couples from the appropriate structural and thermodynamic data. Comparison between the calculated and experimental work-corrected rate constants, kcalcd and kcor, respectively, indicates that almost uniformly kcalcd ≳ kcor, the latter values being typically ca. 10-103-fold smaller. These rate discrepancies are reflected chiefly in the activation entropies, although partly compensated by differences between the experimental and calculated activation enthalpies. Although the values of kcalcd/kcor depend somewhat upon the reaction environment as determined by the nature of the coordinated ligands and the metal surface, they are approximately independent of the magnitude of kcor or the driving force. Taken together, these findings suggest tht the major origin of the discrepancies between kcalcd and kcor is associated with changes in local solvent structure when forming the precursor state. Nonadiabaticity may contribute importantly by necessitating that the reacting centers be in very close proximity. Reactions at "hydrophilic" metal surfaces, such as lead and gallium, that are known to strongly adsorb water molecules yield remarkably similar theory-experiment disparities to those seen with cationic coreactants in homogeneous solution. The markedly closer agreement obtained for some reactions at mercury is attributed to the relatively mild perturbation exerted by this metal surface upon the local solvent structure.
| Original language | English |
|---|---|
| Pages (from-to) | 2795-2804 |
| Number of pages | 10 |
| Journal | Journal of Physical Chemistry |
| Volume | 89 |
| Issue number | 13 |
| Publication status | Published - 1985 |
Fingerprint
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
Cite this
Prediction of electron-transfer reactivities from contemporary theory : Unified comparisons for electrochemical and homogeneous reactions. / Hupp, Joseph T; Weaver, Michael J.
In: Journal of Physical Chemistry, Vol. 89, No. 13, 1985, p. 2795-2804.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Prediction of electron-transfer reactivities from contemporary theory
T2 - Unified comparisons for electrochemical and homogeneous reactions
AU - Hupp, Joseph T
AU - Weaver, Michael J.
PY - 1985
Y1 - 1985
N2 - Suitable theoretical formalisms are outlined for examining and predicting rate parameters for outer-sphere electron transfer in heterogeneous and homogeneous environments on a unified basis. They are utilized to calculate rate constants and activation parameters for 11 electrochemical and 45 homogeneous self-exchange and cross reactions involving transition-metal aquo, ammine, ethylenediamine, and polypyridine redox couples from the appropriate structural and thermodynamic data. Comparison between the calculated and experimental work-corrected rate constants, kcalcd and kcor, respectively, indicates that almost uniformly kcalcd ≳ kcor, the latter values being typically ca. 10-103-fold smaller. These rate discrepancies are reflected chiefly in the activation entropies, although partly compensated by differences between the experimental and calculated activation enthalpies. Although the values of kcalcd/kcor depend somewhat upon the reaction environment as determined by the nature of the coordinated ligands and the metal surface, they are approximately independent of the magnitude of kcor or the driving force. Taken together, these findings suggest tht the major origin of the discrepancies between kcalcd and kcor is associated with changes in local solvent structure when forming the precursor state. Nonadiabaticity may contribute importantly by necessitating that the reacting centers be in very close proximity. Reactions at "hydrophilic" metal surfaces, such as lead and gallium, that are known to strongly adsorb water molecules yield remarkably similar theory-experiment disparities to those seen with cationic coreactants in homogeneous solution. The markedly closer agreement obtained for some reactions at mercury is attributed to the relatively mild perturbation exerted by this metal surface upon the local solvent structure.
AB - Suitable theoretical formalisms are outlined for examining and predicting rate parameters for outer-sphere electron transfer in heterogeneous and homogeneous environments on a unified basis. They are utilized to calculate rate constants and activation parameters for 11 electrochemical and 45 homogeneous self-exchange and cross reactions involving transition-metal aquo, ammine, ethylenediamine, and polypyridine redox couples from the appropriate structural and thermodynamic data. Comparison between the calculated and experimental work-corrected rate constants, kcalcd and kcor, respectively, indicates that almost uniformly kcalcd ≳ kcor, the latter values being typically ca. 10-103-fold smaller. These rate discrepancies are reflected chiefly in the activation entropies, although partly compensated by differences between the experimental and calculated activation enthalpies. Although the values of kcalcd/kcor depend somewhat upon the reaction environment as determined by the nature of the coordinated ligands and the metal surface, they are approximately independent of the magnitude of kcor or the driving force. Taken together, these findings suggest tht the major origin of the discrepancies between kcalcd and kcor is associated with changes in local solvent structure when forming the precursor state. Nonadiabaticity may contribute importantly by necessitating that the reacting centers be in very close proximity. Reactions at "hydrophilic" metal surfaces, such as lead and gallium, that are known to strongly adsorb water molecules yield remarkably similar theory-experiment disparities to those seen with cationic coreactants in homogeneous solution. The markedly closer agreement obtained for some reactions at mercury is attributed to the relatively mild perturbation exerted by this metal surface upon the local solvent structure.
UR - http://www.scopus.com/inward/record.url?scp=0001497714&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0001497714&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0001497714
VL - 89
SP - 2795
EP - 2804
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
SN - 0022-3654
IS - 13
ER -