The Structure and EPR Behavior of Nitroxide Biradical Containing Phosphorus Atom in the Bridge

Two short nitroxide biradicals of similar composition: (H5C6)O=P(OR6)2 (BP) and O=S(OR6)2 (BS), 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, as a function of temperature were characterized by changes in the isotropic 14N hyperfine splitting (hfs) 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 biradical BP were carried out on the DFT/UB3LYPPBE0/cc-pVdTZz and DFT/ROPBE/N07D levels of theory and compared with those of BS. Probable differences in biradicals behavior are discussed. © 2015, Springer-Verlag Wien.