Microsolvation of methylmercury: structures, energies, bonding and NMR constants ( 199 Hg, 13 C and 17 O)

EDISON FLOREZ; ALEJANDRO MALDONADO; GUSTAVO A. AUCAR; JORGE DAVID; ALBEIRO RESTREPO

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 18 p. 1537 - 1550

1463-9076

Hartree?Fock (HF) and second order perturbation theory (MP2) calculations within the scalar and full relativistic frames were carried out in order to determine the equilibrium geometries and interaction energies between cationic methylmercury (CH 3 Hg + ) and up to three water molecules. A total of nine structures were obtained. Bonding properties were analyzed using the Quantum Theory of Atoms In Molecules (QTAIM). The analyses of the topology of electron densities reveal that all structures exhibit apartially covalent HgÁ Á ÁO interaction between methylmercury and one water molecule. Consideration of additional water molecules suggests that they solvate the (CH 3 HgÁ Á ÁOH 2 ) + unit. Nuclear magnetic shield-ing constants s( 199 Hg), s( 13 C) and s( 17 O), as well as indirect spin?spin coupling constants J( 199 Hg? 13 C), J( 199 Hg? 17 O) and J( 13 C? 17 O), were calculated for each one of the geometries. Thermodynamic stability and the values of NMR constants correlate with the ability of the system to directly coordinate oxygen atoms of water molecules to the mercury atom in methylmercury and with the formation of hydrogen bonds among solvating water molecules. Relativistic effects account for 11% on s( 13 C) and 14% on s( 17 O), which is due to the presence of Hg (heavy atom on light atom, HALA effect), while the relativistic effects on s( 199 Hg) are close to 50% (heavy atom on heavy atom itself, HAHA effect). J-coupling constants are highly influenced by relativity when mercury is involved as in J( 199 Hg? 13 C) and J( 199 Hg? 17 O). On the other hand, our results show that the values of NMR constants for carbon and oxygen, atoms which are connected through mercury (C?HgÁ Á ÁO), are highly correlated and are greatly influenced by the presence of water molecules to the relativistic effects due to the mercury atom