Kokorin, A.I., V.N. Khrustalev, and E.N. Golubeva, The Structure and EPR Behavior of Short Nitroxide Biradicals Containing Sulfur Atom in the Bridge. Appl. Magn. Reson., 2014. 45(4): p. 397-409.
Two short nitroxide biradicals of similar composition: S(OR6)2 (1) and O=S(OR6)2 (2), where OR6 is 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine, have been studied by electron paramagnetic resonance spectroscopy, and X-ray structural analysis. Variations of the intramolecular electron spin exchange in the biradicals, dissolved in toluene and ethanol, as a function of temperature were characterized by changes in the isotropic 14N hyperfine splitting constant a, values of the exchange integral J and compared with the X-ray structural data. Thermodynamic parameters of the conformational rearrangements were calculated. Geometry optimization and spin density distribution calculations of biradicals 1 and 2 were carried out on the DFT/UB3LYP/cc-pVdz and DFT/ROPBE/N07D levels of theory. Structural rigidity and probable differences in biradicals behavior are discussed.