Ion atmosphere relaxation controlled electron transfers in cobaltocenium polyether molten salts

Amanda S. Harper, Anthony M. Leone, Dongil Lee, Wei Wang, Srikanth Ranganathan, Mary Elizabeth Williams, Royce W. Murray

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Abstract

A room-temperature redox molten salt for the study of electron transfers in semisolid media, based on combining bis(cyclopentadienyl)cobalt with oligomeric polyether counterions, [Cp 2Co](MePEG 350SO 3), is reported. The transport properties of the new molten salt can be varied (plasticized) by varying the polyether content. The charge transport rate during voltammetric reduction of the ionically conductive [Cp 2Co] (MePEG 350SO 3) molten salt exceeds the actual physical diffusivity of [Cp 2Co] + because of rapid [Cp 2Co] +/0 electron self-exchanges. The measured [Cp 2Co] +/0 electron self-exchange rate constants (k EX) are proportional to the diffusion coefficients (D CION) of the counterions in the melt. The electron-transfer activation barrier energies are also close to those of ionic diffusion but are larger than those derived from optical intervalent charge-transfer results. Additionally, the [Cp 2Co] +/0 rate constant results are close to those of dissimilar redox moieties in molten salts where DCION values are similar. All of these characteristics are consistent with the rates of electron transfers of [Cp 2Co] +/0 (and the other donor-acceptor pairs) being controlled not by the intrinsic electron-transfer rates but by the rate of relaxation of the ion atmosphere around the reacting pair. In the low driving force regime of mixed-valent concentration gradients, the ion atmosphere relaxation is competitive with electron transfer. The results support the generality of the recently proposed model of ionic atmosphere relaxation control of electron transfers in ionically conductive, semisolid materials.

Original languageEnglish
Pages (from-to)18852-18859
Number of pages8
JournalJournal of Physical Chemistry B
Volume109
Issue number40
DOIs
Publication statusPublished - 2005 Oct 13

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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    Harper, A. S., Leone, A. M., Lee, D., Wang, W., Ranganathan, S., Williams, M. E., & Murray, R. W. (2005). Ion atmosphere relaxation controlled electron transfers in cobaltocenium polyether molten salts. Journal of Physical Chemistry B, 109(40), 18852-18859. https://doi.org/10.1021/jp051380j