Features of Spin Exchange in Short-Chain Nitroxide Biradicals in Ionic Liquids |
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Authors: | A. I. Kokorin V. A. Tran G. A. Vorobieva |
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Affiliation: | 1. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russian Federation 2. University of Hanoi, Hanoi, Vietnam
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Abstract: | The intramolecular electron spin exchange has been studied by electron paramagnetic resonance (EPR) spectroscopy in the room temperature ionic liquids (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) and 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF4) for three nitroxide biradicals with analogous structures of the connecting bridge between two >N–O· centers as a function of temperature. Temperature variations of the isotropic nitrogen hyperfine splitting constant a, and exchange integral values |J/a| were determined from EPR spectra and analyzed. Thermodynamic parameters of the conformational rearrangements were obtained. The spin exchange in rather rigid short-chain biradicals dissolved in omimBF4 and bmimPF6 was compared with that in toluene solutions. Interesting features of the spin exchange in biradicals in RTIL were observed and explained as a result of the specific intramolecular conformational transitions. Examples when rather rigid biradical molecules become flexible under an influence of RTIL are reported. |
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