Mercury under Pressure acts as a Transition Metal: Calculated from First Principles.

The inclusion of Hg among the transition metals is readily debated. Recently, molecular HgF4 was synthesized in a low-temperature noble gas but the potential of Hg to form compounds beyond a +2 oxidation state in a stable solid remains unresolved. We propose high-pressure techniques to prepare unusual oxidation states of Hg-based compounds. Using an advanced structure search algorithm and first-principles electronic structure calculations, we find that under high pressure Hg in Hg-F compounds transfers charge from the d orbitals to the F, thus behaving as a transition metal. Oxidizing Hg to +4 and +3 yielded the thermodynamically stable compounds HgF4 and HgF3. The former consists of HgF4 planar molecules, a typical geometry for d(8) metal centers. HgF3 is metallic and ferromagnetic owing to the d(9) configuration of Hg, with a large gap between its partially occupied and unoccupied bands under high pressure.