Revisiting HgCl2: A solution- and solid-state 199Hg NMR and ZORA–DFT computational study

Abstract

The 199 Hg chemical-shift tensor of solid HgCl 2 was determined from spectra of polycrystalline materials, using static and magic-angle spinning (MAS) techniques at multiple spinning frequencies and field strengths. The chemical-shift tensor of solid HgCl 2 is axially symmetric (η = 0) within experimental error. The 199 Hg chemical-shift anisotropy (CSA) of HgCl 2 in a frozen solution in dimethylsulfoxide (DMSO) is significantly smaller than that of the solid, implying that the local electronic structure in the solid is different from that of the material in solution. The experimental chemicalshift results (solution and solid-state) are compared with those predicted by density functional theory (DFT) calculations using the zeroth-order regular approximation (ZORA) to account for relativistic effects.199 Hg spin-lattice relaxation of HgCl 2 dissolved in DMSO is dominated by a CSA mechanism, but a second contribution to relaxation arises from ligand exchange. Relaxation in the solid state is independent of temperature, suggesting relaxation by paramagnetic impurities or defects.

A solid-state 199Hg NMR study of mercury halides

“…For such studies, the importance of including relativistic effects on the electronic structure of mercury compounds has been known for some time [36,39,40]. The fact that electrons may be moving at appreciable fractions of the speed of light requires that relativistically invariant calculations such as the zeroth-order regular approximation (ZORA) with density functional theory (DFT) [25,[41][42][43] be used to calculate the 199 Hg NMR chemical shielding.…”

“…However, recent work [26] has shown that the CS tensor of HgCl 2 appears to be, within experimental error, axially symmetric (η = 0), differing from the literature value of η = 0.12 obtained from an analysis of MAS data [24]. An attempt to use the 199 Hg MAS spectrum of HgBr 2 [25] to determine the principal components of the 199 Hg CS tensor was reported to be unsuccessful due to the coupling to the 79,81 Br. The goal of the present work is to measure the principal elements of the 199 Hg CS tensors of these, and other, mercury halides using wideline NMR techniques on solid, static samples.…”

“…With current calculational capabilities, theoretical studies of Hg in the solid state usually predict only qualitative trends. For example, one such study of HgCl 2 [25] yielded calculated CS spans that were consistently larger than those observed experimentally. Hostettler and Schwarzenbach [8] expressed regret "that ab initio quantum mechanical calculations are not yet available to elucidate the preferred bonding modes of these heavy atoms".…”

“…The 199 Hg variable offset cumulative spectrum (VOCS) [28] of static HgCl 2 , shown in Figure 2 together with a simulation, has been previously published [25]. The 199 Hg MAS spectrum of polycrystalline HgCl 2 is shown in Figure 3A.…”

Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: A comparison of three relativistic computational methods

“…Using ZORA at the density functional theory (DFT) level, Wolff et al 18 showed that mercury NMR shielding constants strongly depend on the structure of mercury halides. Finally, Taylor et al 32 conducted recently a ZORA-DFT study on 199 Hg NMR shielding constants of Hg(CH 3 ) 2 , solid HgCl 2 , and of HgCl 2 complexed with DMSO. To the best of our knowledge, four-component relativistic calculations of NMR shielding constants have not yet been presented for Hg(II) compounds, except that Fukuda et al 23 employed the four-component/Dirac-Hartree-Fock (DHF) (Ref.…”