Matrix Isolated HgCH₃ Radical:  An ESR Investigation

Abstract

The Hg12CH3, Hg13CH3, Hg12CD3, 199Hg12CH3, 201Hg12CH3, 201Hg13CH3, 199Hg12CD3, and 201Hg12CD3 radicals have all been formed in a microwave discharge and isolated in an inert neon matrix. Their electronic structure was established for the first time using electron spin resonance (ESR) spectroscopy. The following magnetic parameters were determined from the experimental spectra, g ⊥ = 1.84525(20), A ⊥(199Hg) = 4337(3) MHz, A ⊥(201Hg) = 1604(1) MHz, A ⊥(13C) = 146(2) MHz, A ⊥(H) = 31(1) MHz, and A ⊥(D) = 5(1) MHz. Estimates were made for the following magnetic parameters, g ∥ = 1.990(5), A ∥(199Hg) = 5658(10) MHz, A ∥(201Hg) = 2094(10) MHz, and A ∥(13C) = 270(25) MHz. The free atom comparison method (FACM) was used to determine the unpaired electron spin density distribution for the radical and to develop a bonding model. The HgCH3 radical results are compared with our previous results for the ZnCH3 and CdCH3 radicals as well as other mercury-containing radicals such as HgH, HgCN, and HgF.

Chemistry and Isotope Fractionation of Divalent Mercury during Aqueous Reduction Mediated by Selected Oxygenated Organic Ligands

“…In contrast, recombination of the triplet radical pair is spin-forbidden, and when the pair separates, RO–Hg •+ becomes available for reduction tentatively by AQH 2 (OH)­DS, leading to volatile Hg 0 being split off (Figure S9). The large magnitude of odd-MIF imparted indicates an efficient ISC between the radical pairs, which is supported by the larger HFC constants for mercurous radicals with ionic character . In turn, the decrease in Hg 0 production in the oxic environment (Table S6) is due to a number of interacting factors, as indicated in Figure S8: trapping of mercurous radicals (RO–Hg •+ ) and excited triplets of AQDS, as well as of AQH­(OHg)­DS by ground-state dissolved O 2 .…”

“…The large magnitude of odd-MIF imparted indicates an efficient ISC between the radical pairs, which is supported by the larger HFC constants for mercurous radicals with ionic character. 68 In turn, the decrease in Hg 0 production in the oxic environment (Table S6) is due to a number of interacting factors, as indicated in Figure S8: trapping of mercurous radicals (RO−Hg •+ ) and excited triplets of AQDS, as well as of AQH(OHg)DS by ground-state dissolved O 2 .…”

Mercury Magnetic Isotope Effect: A Plausible Photochemical Mechanism

“…This rate is not easy to access, however, because HFC constants have only been determined for a handful of Hg-containing radicals (see Table S2). − The isotropic HFC constants range from 0.7 cm –1 for 199 HgF to 0.2 cm –1 for 199 HgCH 3 , suggesting that the HFC for ClHg • is likely within this range. The HFCs are high enough to induce significant electron-nuclear polarization by the radical pair mechanism at zero and low magnetic fields .…”

Analytic Calculation of Isotropic Hyperfine Structure Constants Using the Normalized Elimination of the Small Component Formalism

“… a The augmented SARC basis set is used for mercury, TZVpp for silver, and the 6-311+G(2df,p) basis set for all other atoms. In parentheses, the values obtained using the uncontracted Dyall’s TZ basis set for mercury and uncontracted aug-cc-pVTZ for other atoms (see section for more details). b Obtained in ref from measurement in a neon matrix. c Obtained in ref from measurement in an argon matrix. d Obtained in ref from measurement in an argon matrix. e Obtained in ref from measurement in an argon matrix. f Obtained in ref from measurement in a neon matrix. g Taken from ref . …”