EPR study of gamma-irradiated diaminoglyoxime single crystals

Gamma irradiated single crystals of diaminoglyoxime (DAG), were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature and at different orientations in the magnetic field. Taking the chemical structure and the experimental spectra of the irradiated DAG single-crystal into consideration we assumed that iminoxy type paramagnetic species were produced where the unpaired electron is delocalized on N atoms. Depending on this assumption, an iminoxy radical was modeled and EPR parameters were calculated using the MP2/6-311++G(d,p)-level of theory and then the calculated hyperfine-coupling constants were used as initial guess for simulations. The experimental and simulated spectra for each of the three crystallographic axes well matched with the modeled radical. We thus identified an iminoxy radical as a paramagnetic species produced in DAG. The experimental g-factor and theoretically calculated hyperfine coupling constants of this radical were found to be anisotropic, with the average values giso = 2.0150, aN(4) = −2.71 mT, aN(3) = 1.46 mT, aN(9) = 0.29 mT, aN(12) = 0.51 mT, aH(10) = −0.53 mT, aH(11) = −0.55 mT, aH(13) = −0.36 mT and aH(14) = −0.42 mT, respectively.