Relativistic ab initio and density functional theory calculations on the mercury fluorides: Is HgF4 thermodynamically stable?

Structural and energetic properties of the experimentally yet unknown gas-phase molecule mercury(IV) fluoride HgF4 have been calculated with three independent quantum-chemical approaches accounting for relativistic and electron correlation effects. All-electron 4-component density functional and scalar relativistic direct perturbation theory as well as valence-only quasi-relativistic pseudopotential calculations predict HgF4 to be thermodynamically stable by at least 19 kJ/mol with respect to HgF2 and F2, and by at least 690 kJ/mol with respect to atomization. The Hg–F bond length and the totally symmetric Hg–F stretching mode are predicted to be 1.910±0.015 Å and 565±25 cm−1, respectively. HgCl4 is predicted to be unstable with respect to HgCl2 and Cl2. The ionization potentials and excitation energies of the Hg atom and its cations are presented.