Theoretical study of substituted methyl mercury in gas phase and in solution

Abstract

Quantum chemistry calculations were carried out, using density functional theory, in order to investigate the thermodynamic properties, enthalpy (ΔH), Gibbs free energy (ΔG) and equilibrium constant (K_eq), for the dissociation of a series of methylmercury series compounds. Two kind of pseudopotentials were studied, the relativistic compact effective potentials and the Stuttgart pseudopotential. The B3LYP, BLYP, BP86 and BMK functionals were employed. The calculations were performed in gas phase and in presence of solvent. The results reveal that, none of the studied functionals was able to reproduce the experimental C-Hg and Hg-X, X=Cl, Br and I bond distances. The presence of solvent, water, acetonitrile and dimethylsulfoxide, has a strong influence on the ΔH and ΔG values. On the other hand, the results show that there is a lineal correlation between the logarithm of the experimental K_eq(exp) and the calculated K_eq(theo). This type of correlation could be useful in the resolution of problems related with the contamination by methylmercury compounds.