The solvation of the mercury(II) ion—a199Hg NMR study

Abstract

The solvation of the mercury(II) ion in solvents with different solvation properties, water, dimethylsulfoxide, N,N-dimethylthioformamide, and liquid ammonia, has been studied by means of (199)Hg NMR. The (199)Hg chemical shift shows a pronounced dependence on the coordination number of the mercury(II) ion in the solvates resulting in a difference of over 1200 ppm between basically tetrahedral and octahedral complexes. The chemical shifts can furthermore be associated with electron-pair donor properties of the solvents. The spin-lattice relaxation times of the (199)Hg nucleus in the solvates have been measured at different applied magnetic fields, concentrations, temperatures, and isotope substitutions. Possible mechanisms for the (199)Hg relaxation were proposed and the chemical shielding anisotropy in the solvates has been estimated. The (199)Hg relaxation rates and the anisotropy are correlated with the structure of the solvate complexes in solution obtained from recent LAXS and EXAFS studies.

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

“…For example, in the same solvent, a solvated mercury cation should show the same chemical shift for both the chloride and the acetate, as the mercury atom would be coordinated to the same ligand. However, such behavior is usually observed only with the perchlorate or triflate [7]. That such dissociation does not occur for mercuric chloride is demonstrated in Figure 3.…”

“…These issues include concentration effects, difficulties arising from the dryness of the solvent, pH of the medium, and potential decoupling difficulties. Maliarik and Persson [7] have noted that "the 199 Hg chemical shifts can be misleading and non-reproducible unless the temperature is correctly specified or, preferably, the temperature dependence of the chemical shift of the studied species is determined". To address a possible temperature dependence of the secondary standard, the variation with temperature of the 199 Hg chemical shift of HgCl 2 in d 6 -DMSO was carefully evaluated, as shown in Figure 1.…”

“…A compilation by Wrackmeyer and Contreras [4] contains a substantial tabulation of solution-state 199 Hg chemical shifts. The 199 Hg relaxation properties of neat mercury-containing liquids and mercury compounds dissolved in solvents ranging from alcohols and water to organic liquids have also been examined [5][6][7][8][9]. For smaller molecules such as dimethylmercury, Hg(CH 3 ) 2 , and for the Hg 2+ ion in aqueous solution investigated at the low resonance frequencies encountered when using electromagnets with fields of 2.35 T or less, spin-lattice relaxation is generally dominated by the spin-rotation interaction [4,5].…”

“…However, many reports indicate that the chemical-shift-anisotropy (CSA) mechanism dominates the 199 Hg spin-lattice relaxation in mercury compounds in solution at field strengths greater than 4.7 T [4,6]. Recently, Maliarik and Persson [7] have noted that "despite the number of 199 Hg NMR studies undertaken, information on the relaxation behavior of this nucleus is relatively scarce and is mostly related to linear organometallic HgR 2 complexes". Maciel and Borzo [8] reported that the relaxation in mercuric chloride (HgCl 2 ) at 1.4 M in ethanol is exponential, with a 199 Hg T 1 of 1.4 s at ambient temperature.…”

Phosphonium Chloromercurate Room Temperature Ionic Liquids of Variable Composition

“…10 63 199 Hg NMR as a technique for the investigation of biomolecules 64 and for advanced theoretical investigation of NMR parameters has gained in popularity in recent years. Maliarik et al 65 and Nilsson et al 66 published their results on the effects of different solvent molecules (water, ammonia, trialkylphosphines, and -phosphites) on the Hg 2+ coordination and the subsequent effects of temperature, concentration, etc. on the chemical shift observable by 199 Hg NMR.…”