Hydration of Hg2+ in Aqueous Solution Studied by Neutron Diffraction with Isotopic Substitution

O. Sobolev (1) , G. J. Cuello (2) , G. Roman Ross (3) , N. T. Skipper (4) , L. Charlet (1)

1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique
2 ILL - Institut Laue-Langevin
3 Department of Chemistry, Faculty of Sciences
4 Department of Physics and Astronomy [UCL London]

The structural parameters of Hg2+ hydration were studied in 0.225 mol/L solutions of Hg2+ in DNO3/D2O by means of neutron diffraction with isotopic substitution of 199Hg for natHg. It was found that Hg2+ is hydrated by a first solvation shell of six water molecules. The observed Hg−O and Hg−H distances are equal to 2.48 ± 0.05 and 3.08 ± 0.05 Å, respectively. The angle phi between the plane of the water molecule and the cation−water oxygen axis is 35°. The solvation of Hg2+ therefore mimics very closely that of Ca2+ (the Ca−O and Ca−H distances are 2.40 and 3.03 Å, respectively) and helps to account for the extreme toxicity of mercury(II). We note also that the Hg−O distance obtained in the neutron diffraction experiment is larger by 0.1 Å than that obtained by X-ray diffraction. This difference is consistent with a shift of the oxygen electron density toward the mercury cation due to the covalency of the Hg−O interaction.

O. Sobolev, G. J. Cuello, G. Roman Ross, N. T. Skipper, L. Charlet. Hydration of Hg2+ in Aqueous Solution Studied by Neutron Diffraction with Isotopic Substitution. Journal of Physical Chemistry A, 2007, 111 (24), pp.5123 à 5125. ⟨10.1021/jp072650w⟩. ⟨insu-00347890⟩