RADICAL CATIONS IN MIXTURES OF CL3P AND ME2S - A COMBINED ESR AND QUANTUM CHEMICAL STUDY

Exposure of phosphorus trichloride (Cl3P) and dimethyl sulfide (Me2S) dissolved in halocarbons (CFCl3, CF3CCl3, CF2ClCFCl2, and CH2Cl2) to X rays at 77 K results in the corresponding parent cations and several cation-substrate adducts. The radicals are detected and identified by ESR spectroscopy. In dilute solution exclusive formation of the parent Cl3P.+ and Me2S.+ radical cations is observed. In CFCl3, Me2S.+ exhibits superhyperfine interactions due to chlorine and fluorine nuclei of the matrix molecule(s). At increased concentration, or on warning the sample, the parent radical cations readily react with dissolved Cl3P or Me2S molecules to form homodimeric Cl3P-PCl3+ and Me2S-SMe2+ and heterodimeric Cl3P-SMe2+ radical cations with a two-center three-electron sigma(2)sigma*1 bond. The heterodimer is formed in spite of a significant difference between the ionization potentials of the two constituents in reduced form. On further annealing, the Cl3P-PCl3+ cation rearranges to the well-known trigonal-bipyramidal Cl4P. radical and an as yet unidentified configuration. Candidates for the latter are proposed. In concentrated frozen solutions an unexpected reaction of Me2S-SMe2+ and Cl3P is observed, resulting in the heterotrimer Cl3P(SMe2)2*+ with an octahedral configuration, exhibiting a very large P-31 hyperfine interaction (A(iso) = 5115 MHz). Extensive ab initio calculations at the HF/3-21G+ level, including calculation of isotropic and dipolar electron-nuclear hyperfine interactions, confirm the assignments and provide detailed insight into the molecular geometry, electronic configuration, and stability of the radical products.