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Ion pairing effects on bis(hydrazine) intervalence radical cations

Nelsen, Stephen F. and Ismagilov, Rustem F. (1999) Ion pairing effects on bis(hydrazine) intervalence radical cations. Journal of Physical Chemistry A, 103 (27). pp. 5373-5378. ISSN 1089-5639. doi:10.1021/jp991294h.

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Three bis(2-tert-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl) radical cation salts, bridged by 2,3,5,6-tetramethylbenzene-1,4-diyl (1^+PF_6^-), biphenylene-4,4‘-diyl (2^+PF_6^-), and 9,9-dimethyl-fluorene-2,7-diyl (3^+NO_3^-) groups, have been studied in methylene chloride. The transition energy at band maximum (E_(op)) increases as concentration increases and when ^nBu_4+BF_6^- is added, indicating that ion pairing increases E_(op). The E_(op) data fit a simple ion pairing equilibrium, giving ion pairing equilibrium constants at 293 K of 3100, 3100, and 6100 M^(-1), respectively. Electron-transfer rate constants measured by ESR are reported for 0.19 mM 2^+PF_6^- and for 1 mM 2^+PF_6^- and 3^+NO_3^- in the presence of 20 mM ^nBu_4+BF_6^- in methylene chloride. Prediction of k_(ET) from the optical spectrum of 2^+PF_6^- containing excess ^nBu_4^+BF_6^- was made both assuming the optical ET is endoenthalpic by an amount calculated from the increase in E_(op), and that ΔG° = 0 (that is, that the ion pairing effect may be lumped into the electron transfer coordinate along with the vertical and solvent reorganization effects). The predicted rate constant for the latter is only a factor of 2.5 times larger the former, so both agree rather well with the ESR-derived rate constant.

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Ismagilov, Rustem F.0000-0002-3680-4399
Additional Information:Copyright © 1999 American Chemical Society. Published In Issue: July 08, 1999. Received April 20, 1999. Revised April 28, 1999. We thank the National Science Foundation for support of parts of this work under grant CHE-9417946, the NSF major instrument program and the University of Wisconsin for funds used in purchase of the spectrometers and computer equipment used, and the Dow Chemical Company for a fellowship for R.F.I. We thank Jeff Curtis (University San Francisco) for valuable discussions.
Funding AgencyGrant Number
University of WisconsinUNSPECIFIED
Dow Chemical CompanyUNSPECIFIED
Subject Keywords:intramolecular electron-transfer; metal-complexes; charge- transfer; transition; dependence; strength; units
Issue or Number:27
Record Number:CaltechAUTHORS:20130821-160726092
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40838
Deposited By: Whitney Barlow
Deposited On:28 Aug 2013 22:39
Last Modified:10 Nov 2021 00:09

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