Coupled cluster calculations using single and double excitations (CCSD) are carried out on the compounds HgX+, HgX2, HgX3-, and HgX42- (X = Cl, Br, I, CN, and SCN) to determine their structures in the gas phase. Solvation calculations using polarized continuum model with a conductor-like screening reaction field (CPCM) were carried out at the CCSD level on the optimized structures of these molecules to calculate their stepwise standard Gibbs free energy of formation in aqueous medium (Delta G(aq)degrees) starting from simple Hg2+ and X ions. The computed DG(aq)degrees could be correlated linearly with experimental data. (C) 2010 Elsevier B.V. All rights reserved.