Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- Versus tert-butyl-substituted Os(III) polypyridyl complexes

Thomas W. Hamann, Bruce S. Brunschwig, Nathan S Lewis

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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 languageEnglish
Pages (from-to)25514-25520
Number of pages7
JournalJournal of Physical Chemistry B
Volume110
Issue number50
DOIs
Publication statusPublished - Dec 21 2006

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2,2'-Dipyridyl
Charge transfer
Rate constants
electron transfer
Osmium
charge transfer
osmium
Electrons
spacers
Capacitance
Current density
capacitance
Nuclear magnetic resonance
current density
nuclear magnetic resonance
Electrodes
electrodes
electronics

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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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 journalArticle

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