EPR study of a gamma-irradiated (2-hydroxyethyl)triphenylphosphonium chloride single crystal

Abstract

In this study, gamma-irradiated single crystals of (2-hydroxyethyl)triphenylphosphonium chloride [CH(2)CH(2)OHP(C(6)H(5))(3)Cl] were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature for different orientations in the magnetic field. The single crystals were irradiated with a (60)Co-gamma-ray source at 0.818 kGy/h for about 36 h. Taking the chemical structure and the experimental spectra of the irradiated single crystal of the title compound into consideration, a paramagnetic species was produced with the unpaired electron delocalized around (31)P and several (1)H nuclei. The anisotropic hyperfine values due to the (31)P nucleus, slightly anisotropic hyperfine values due to the (1)H nuclei and the g-tensor of the radical were measured from the spectra. Depending on the molecular structure and measured parameters, three possible radicals were modeled using the B3LYP/6-31+G(d) level of density-functional theory, and EPR parameters were calculated for modeled radicals using the B3LYP/TZVP method/basis set combination. The calculated hyperfine coupling constants were found to be in good agreement with the observed EPR parameters. The experimental and theoretically simulated spectra for each of the three crystallographic axes were well matched with one of the modeled radicals (discussed in the text). We thus identified the radical (C) over dotH(2)CH(2)P(C(6)H(5))(3)Cl as a paramagnetic species produced in a single crystal of the title compound in two magnetically distinct sites. The experimental g-factor and hyperfine coupling constants of the radical were found to be anisotropic, with the isotropic values g(iso)(=)2.0032, A(rad)(P2) = 118.6G, A(CH2)(H23) = 28.4G, A(CH2)(H24) = 4.2 G and A(CH2)(H40-41) = 18.5 G for site 1 and g(iso) = 2.0031, A(rad)(P2) = 118.9G, A(CH2)(H23) = 28.5 G A(CH2)(H24) = 4.3G and A(CH2)(H40-41) = 17.3 G for site 2.