STRUCTURE OF SELENIUM-CENTERED RADICALS - ELECTRON-SPIN RESONANCE STUDY OF R2SEHAL TRAPPED IN SINGLE-CRYSTALS

X-irradiated single crystals of Ph3SeBr, Ph2SeBr2, and Ph2SeCl2 have been studied by ESR spectroscopy. In each crystal a radical species exhibiting anisotropic hyperfine interaction with the halogen nuclei has been trapped. The ḡ tensors, the magnetic hyperfine tensors to the halogen nuclei, and the 81Br quadrupolar interaction tensors have been determined. The 77Se magnetic hyperfine tensor has also been obtained for the radical species trapped in Ph2SeBr2 and Ph2SeCl2. These tensors lead to the identification of Ph2ṠeHal. The spin distribution is discussed; the unpaired electron lies probably in a Se-Hal σ* orbital which is oriented perpendicularly to the CSeC plane. The spin distribution seems to be very sensitive to the nature of the host matrix. © 1979 American Chemical Society.