Potential rules for stable transition metal hexafluorides with high oxidation states under high pressures

High pressure is a powerful tool in material sciences which can lead to the discovery of novel inorganic species in high oxidation states. Based on the prediction of the stability of PdF6 with a high Pd oxidation state of +6, we propose three potential guiding rules for finding stable transition metal (TM) fluorides with high +6 oxidation states: (1) the existence of a large (>7 eV) valence orbitals energy differences of atoms between the TM d orbital and the F 2p orbital; (2) an appropriate number of valence electrons within the range of 6-11; and (3) suitable electronegativity values less than 2.3 on the Pauli scale. More importantly, by synergistically invoking all of these rules, we predict, by combining a particle swarm optimization algorithm with first-principles calculation on the phase stabilities of the various TM-F compounds, a collection of new TMF6 species with the space group Pnma that have a +6 oxidation state. Subsequently, we develop an understanding of the high +6 oxidation state for the TM elements. These findings are expected to play a crucial role in the predictive discoveries of new fluorides with high oxidation states of +6.

Automated summary

High pressure is a powerful tool for discovering novel inorganic species in high oxidation states, such as the stable transition metal fluorides with a +6 oxidation state. We propose three guiding rules based on the stability prediction of PdF6 to find these stable TM fluorides, and successfully predict new TMF6 species with the space group Pnma and a +6 oxidation state using a particle swarm optimization algorithm and first-principles calculations. These findings provide an understanding of the high +6 oxidation state for TM elements and are important for predictive discoveries of new fluorides with high oxidation states.