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Behavior of Short Nitroxide Biradical in Room Temperature Ionic Liquids |
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| Authors: | A. I. Kokorin B. Mladenova E. N. Golubeva G. Grampp |
| Affiliation: | 1. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russian Federation 3. Institute of Physical and Theoretical Chemistry, Graz University of Technology, Graz, Austria 2. M. Lomonosov Moscow State University, Moscow, Russian Federation |
| Abstract: | The intramolecular electron spin exchange in short nitroxide biradical O=S(OR6)2 (I), where OR6 is 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine, dissolved in the room temperature ionic liquids (RTILs) 1-octyl-3-methylimidazolium hexafluorophosphate (omimPF6), 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF4), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), and 1-ethyl-3-methylimidazolium tetrafluoroborate (emimBF4) has been studied by electron paramagnetic resonance (EPR) spectroscopy as a function of temperature. Temperature variations of the isotropic nitrogen hyperfine splitting constant a were measured from EPR spectra. Thermodynamic parameters of the conformational rearrangements were calculated and compared with literature data. These intramolecular movements in rather rigid short-chain biradical I dissolved in four different RTILs are described well by the Debye–Stokes–Einstein law. Unrestricted density-functional-theory calculations of the geometry and electronic structure of the biradical were carried out using the ORCA program package, and showed that the O=S< group is available for the interaction with anions and cations of RTIL. The possible mechanism of such conformational transitions in biradical I in RTIL is discussed. |
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