Anisotropic Electron Spin Resonance Spectra of PCl2 and NCl2 in Low Temperature Matrices

Well‐resolved ESR spectra of PCl₂ were observed from the thermolysis (1000°C) of PCl₃, in argon, krypton, xenon, and nitrogen matrices. Satisfactory computer simulated spectra were obtained using two slightly different interpretations. One assumed a rhombic g tensor and an axially symmetric phosphorus hyperfine tensor; $g_{\mathrm{xx}}{\text{=2.0024,\hspace{0.17em}g}}_{\mathrm{yy}}{\text{=20011,\hspace{0.17em}g}}_{\mathrm{zz}}{\text{=1.9962;\hspace{0.17em}C}}_{\parallel }\text{(P)=293\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\perp }(\mathrm{P}\text{)=± 30.5\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\parallel }(\mathrm{Cl}\text{)=17.5\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\perp }(\mathrm{Cl}\text{) <0.3\hspace{0.17em}}\mathrm{G}$ . The other assumed an axial g tensor and a rhombic phosphorus hyperfine tensor; $g_{\parallel }{\text{= 2.0024,\hspace{0.17em}g}}_{\perp }{\text{= 1.9986;\hspace{0.17em}C}}_{\mathrm{xx}}(\mathrm{P}\text{)=293\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\mathrm{yy}}(\mathrm{P}\text{)=± 39.0\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\mathrm{zz}}(\mathrm{P}\text{)=± 22.5\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\parallel }(\mathrm{Cl}\text{)=17.5\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\perp }(\mathrm{Cl}\text{)<0.3\hspace{0.17em}}\mathrm{G}$ . In situ photolysis of PCl₃ in argon produced a spectrum tentatively assigned to the asymmetric PClCl radical. The ESR spectrum due to NCl₂ radicals was observed from a direct room temperature sprayon of NCl₃ mixed with nitrogen or argon. Experiments using ¹⁵NCl₃ were also performed. The following assignment was obtained: $g_{\mathrm{xx}}{\text{=2.006,\hspace{0.17em}g}}_{\mathrm{yy}}{\text{=2.025,\hspace{0.17em}g}}_{\mathrm{zz}}{\text{=2.023;\hspace{0.17em}C}}_{\mathrm{xx}}{(}^{14}\mathrm{N}\text{)=40\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\mathrm{yy}}{(}^{14}\mathrm{N}\text{)=14\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\mathrm{zz}}{(}^{14}\mathrm{N}\text{)=6\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\parallel }(\mathrm{Cl}\text{)=24\hspace{0.17em}}\mathrm{G}{\mathrm{;\hspace{0.17em}C}}_{\perp }(\mathrm{Cl}\text{)=17\hspace{0.17em}}\mathrm{G}$ . A discussion of the spin density distribution in the nitrogen and phosphorus dihalide radicals (NF₂, NCl₂, PF₂, and PCl₂) and of the electronic structure of these species using the available experimental data, atomic electronegativities, and the results of extended Hückel molecular orbital calculations is presented. Some information on the decomposition reactions of NCl₃ was obtained. A test of the reference values of the atomic nuclear moment—valence electron spin coupling parameters is possible by using the total spin densities determined for these radicals. The reference values calculated by Hurd and Cooden are shown to be preferable.