Abstract
Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4′-di-methyl-2,2′-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4′-di-tert-butyl-2, 2′-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of ∼50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu 2bpy)3]3+/2+ and [Os(Me2bpy) 3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes.
| Original language | English |
|---|---|
| Pages (from-to) | 25514-25520 |
| Number of pages | 7 |
| Journal | Journal of Physical Chemistry B |
| Volume | 110 |
| Issue number | 50 |
| DOIs | |
| Publication status | Published - Dec 21 2006 |
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ASJC Scopus subject areas
- Physical and Theoretical Chemistry
Cite this
Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- Versus tert-butyl-substituted Os(III) polypyridyl complexes. / Hamann, Thomas W.; Brunschwig, Bruce S.; Lewis, Nathan S.
In: Journal of Physical Chemistry B, Vol. 110, No. 50, 21.12.2006, p. 25514-25520.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- Versus tert-butyl-substituted Os(III) polypyridyl complexes
AU - Hamann, Thomas W.
AU - Brunschwig, Bruce S.
AU - Lewis, Nathan S
PY - 2006/12/21
Y1 - 2006/12/21
N2 - Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4′-di-methyl-2,2′-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4′-di-tert-butyl-2, 2′-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of ∼50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu 2bpy)3]3+/2+ and [Os(Me2bpy) 3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes.
AB - Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4′-di-methyl-2,2′-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4′-di-tert-butyl-2, 2′-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of ∼50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu 2bpy)3]3+/2+ and [Os(Me2bpy) 3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes.
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U2 - 10.1021/jp0649697
DO - 10.1021/jp0649697
M3 - Article
VL - 110
SP - 25514
EP - 25520
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
SN - 1520-6106
IS - 50
ER -