High-pressure stabilization of open–shell bromine fluorides

Abstract

Halogen fluorides are textbook examples of how fundamental chemical concepts, such as molecular orbital theory or the valence-shell electron-repulsion (VSEPR) model, can be used to understand the geometry and properties of compounds. However, it is still an open question whether these notions are applicable to matter subject to high pressure (>1 GPa). In an attempt to gain insight into this phenomenon, we present a computational study on the phase transitions and reactivity of bromine fluorides at pressures of up to 100 GPa (≈10⁶ atm). We predict that at a moderately high pressure of 15 GPa, the bonding preference in the Br/F system should change considerably with BrF₃ becoming thermodynamically unstable and two novel compounds emerging as stable species: BrF₂ and BrF₆. Calculations indicate that both these compounds contain radical molecules while being non-metallic. We propose a synthetic route for obtaining BrF₂ which does not require the use of highly reactive elemental fluorine. Finally, we show how molecular orbital diagrams and the VSEPR model can be used to explain the properties of compressed bromine fluorides.