Radical cations of dialkylmercury derivatives, radiation synthesis and electron spin resonance detection

Abstract

Exposure of very dilute solutions of Hg(CD₃)₂ in tetrachloromethane to ⁶⁰Co γ-rays at 77 K gave a species whose e.s.r. spectrum is characteristic of the parent cation. Interpretation of the g-values and ¹⁹⁹Hg tensor component B derived from a computer synthesis of the spectrum suggests that the unpaired electron is strongly confined to the linear σ orbital having a node through the mercury atom. This has a large 6p(Hg) character. No extra features were obtained using Hg(¹³CH₃)(CH₃), confirming that the spin density on the CH₃ groups is small (<20%). When CFCl₃ was the solvent extra poorly defined splittings were observed which are assigned to weak, but specific interaction with one solvent molecule (¹⁹F). The spectra for Hg(CH₃)₂ in this solvent were analysed in terms of the same solvent features together with coupling to at least five and probably seven protons. The small ¹H coupling was almost isotropic at ±4.5 G. In contrast, Hg(C₂H₅)₂ gave no resolved coupling to ¹⁹F, but there was a large, well defined, triplet splitting (42 G) assigned to two specific CH₃ protons. This suggests that rotation about the C–C bonds is restricted. We were unable to detect free rotation on annealing, although the lines broadened considerably, prior to radical loss. Attempts to detect ˙CH₃ or ˙CH₂CH₃ radicals in these systems were unsuccessful, but clear evidence for ˙CD₃ radicals was obtained for Hg(CD₃)₂ in CFCl₃ on annealing.