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Title: The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane

Abstract

A massive structural change accompanies electron capture by the 1,2-dicarba-closo-dodecaborane cage molecule (1). Bimolecular electron transfer (ET) by pulse radiolysis found a reduction potential of E0 = –1.92 V vs Fc+/0 for 1 and rate constants that slowed greatly for ET to or from 1 when the redox partner had a potential near this E0. Moreover, two electrochemical techniques could detect no current at potentials near E0, finding instead peaks or polarographic waves near –3.1 V, which is 1.2 V more negative than E0. Voltammetry could determine rate constants, but only near –3.1 V. DigiSim simulations can describe the irreversible voltammograms but require electrochemical rate constants near 1 × 10–10 cm/s at E0, a factor of 10–10 relative to molecules undergoing facile ET. This factor of 10–10 compared to ~10–5 for bimolecular ET introduces a puzzle. This puzzle can be understood as a manifestation of one of the “Frumkin Effects” in which only part of the applied voltage is available to drive ET at the electrode.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [2];  [2];  [3]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Czech Academy of Sciences, Prague (Czech Republic)
  3. Univ. of Colorado, Boulder, CO (United States); Czech Academy of Sciences, Prague (Czech Republic)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1572367
Report Number(s):
BNL-212237-2019-JAAM
Journal ID: ISSN 1520-6106; TRN: US2001322
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
Journal Volume: 123; Journal Issue: 45; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; Homogeneous vs heterogeneous electron transfer; reorganization energy; cyclic voltammetry; pulse radiolysis; overpotential; Frumkin Effect; free energy relation; carborane

Citation Formats

Miller, John R., Cook, Andrew R., Šimková, Ludmila, Pospíšil, Lubomír, Ludvík, Jiří, and Michl, Josef. The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane. United States: N. p., 2019. Web. https://doi.org/10.1021/acs.jpcb.9b08151.
Miller, John R., Cook, Andrew R., Šimková, Ludmila, Pospíšil, Lubomír, Ludvík, Jiří, & Michl, Josef. The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane. United States. https://doi.org/10.1021/acs.jpcb.9b08151
Miller, John R., Cook, Andrew R., Šimková, Ludmila, Pospíšil, Lubomír, Ludvík, Jiří, and Michl, Josef. Fri . "The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane". United States. https://doi.org/10.1021/acs.jpcb.9b08151. https://www.osti.gov/servlets/purl/1572367.
@article{osti_1572367,
title = {The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane},
author = {Miller, John R. and Cook, Andrew R. and Šimková, Ludmila and Pospíšil, Lubomír and Ludvík, Jiří and Michl, Josef},
abstractNote = {A massive structural change accompanies electron capture by the 1,2-dicarba-closo-dodecaborane cage molecule (1). Bimolecular electron transfer (ET) by pulse radiolysis found a reduction potential of E0 = –1.92 V vs Fc+/0 for 1 and rate constants that slowed greatly for ET to or from 1 when the redox partner had a potential near this E0. Moreover, two electrochemical techniques could detect no current at potentials near E0, finding instead peaks or polarographic waves near –3.1 V, which is 1.2 V more negative than E0. Voltammetry could determine rate constants, but only near –3.1 V. DigiSim simulations can describe the irreversible voltammograms but require electrochemical rate constants near 1 × 10–10 cm/s at E0, a factor of 10–10 relative to molecules undergoing facile ET. This factor of 10–10 compared to ~10–5 for bimolecular ET introduces a puzzle. This puzzle can be understood as a manifestation of one of the “Frumkin Effects” in which only part of the applied voltage is available to drive ET at the electrode.},
doi = {10.1021/acs.jpcb.9b08151},
journal = {Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry},
number = 45,
volume = 123,
place = {United States},
year = {2019},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Figures / Tables:

Figure 1 Figure 1: Optimized structures (b3lyp/6-31g(d)) of 1. The neutral (left) is a nearly dodecahedryl closo-carborane having a C-C bond length of 1.62 Å. In the radical anion the C-C bond length expands to 2.39 Å and further in the dianion to 2.55 Å to become a nido structure (right).

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