Journal of Physical Chemistry p. 5845 - 5851 (1984)
Update date:2022-08-17
Topics:
Rieger, Anne L.
Rieger, Philip H.
In an attempt to resolve ambiguities in and contradictions among previous studies, NMR spectra of the methylviologen (MV2+), benzylviologen (BV2+), and diquat (DQ2+) dications and ESR spectra of the corresponding cation radicals were reinvestigated.ESR spectra of the cation radicals in methanol solution had sufficiently good signal-to-noise ratios and resolution to permit completely unambiguous determinations of hyperfine coupling constants.ESR intensity data showed that MV+. and BV+. precipitate as ESR-inactive solids at low temperature and that MV+. associates to micelle-like solution particles at high concentration.The intensity data show no evidence for formation of dimers or other low molecular weight polymers.Literature reports of dimer formation in methanol solution are the result of temperature-dependent saturation of the ESR spectra.Line broadening of NMR spetra of MV2+, BV2+, or DQ2+ in the presence of traces of cation radical was used to provide unambiguous assignments of ESR hyperfine coupling constants, and to give good estimates of the cation radical concentrations and the dication/cation radical electron exchange rate constant.The NMR line broadening experiments also provide an estimate of the rate of conformational change of the ethylene bridge in the diquat cation radical.
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