THEORETICAL STUDIES ON THE FORMATION OF MERCURY COMPLEXES IN SOLUTION AND THE DISSOLUTION AND REACTIONS OF CINNABAR

Abstract

Expanding upon our previous studies of the properties of Au complexes, we present calculations for several Hg (super 2+) species in aqueous solution and for molecular models for cinnabar. Hydration effects are treated with a combination of "supermolecule" calculations containing several explicit water molecules and polarizable continuum calculations. We focus upon the following problems: (1) calculation of the stabilities of HgL 2 , L = F (super -) , Cl (super -) , OH (super -) , SH (super -) , and CN (super -) and HgCl n (super 2-) n n = 1-4; (2) development of a molecular model for cinnabar of the form Hg 3 S 2 (SH) 2 ; and (3) dissolution or adsorption reactions using this cinnabar model. The absolute and relative formation enthalpies of the HgL 2 species can be satisfactorily reproduced at the Hartree-Fock plus Moller-Plesset second order correlation correction level using relativistic effective core potential basis sets if the hydration of neutral HgL 2 is explicitly taken into account. Evaluating the energetics for the series of complexes HgCl n (super 2-) n is more difficult, because great accuracy is needed in the large hydration energies and some of the species are highly nonspherical. The Hg 3 S 2 (SH) 2 species shows an equilibrium structure very much like that in cinnabar. The relative energetics for dissolution of cinnabar by H 2 O, H 2 S, SH (super -) , and SH (super -) +elemental S are correctly reproduced using this model molecule. Calculations on Hg 3 S 2 ClI provide a model for understanding the adsorption of I (super -) ions on cinnabar surfaces in the presence of Cl (super -) .