How High Does the Pressure Need to Be to Produce Internoble-Gas Ionic Compounds?

Noble gases (NGs) are widely distributed in the universe with billions-year long lifetimes due to their closed-shell electronic structures with little chemical reactivity. Recent studies have found that most NGs can form covalent or ionic compounds with open-shell neutral atoms (e.g., O, Fe, and Ni) in conditions similar to planetary interiors. However, there are still rare reports of chemical bonding among NG elements themselves. To date, NG solids with only weak intermolecular interactions have been found. Herein, we present the first theoretical evidence of the formation of inter-NG ionic compounds beyond terapascal (TPa) pressures. We performed ab-initio computations combined with crystal-structure predictions and showed that Kr and Xe can act as oxidant and reductant, respectively, above 1.5 TPa. Notably, the conventional octet rule for chemical compounds is inapplicable here due to the abnormal charge transfer upon ionic bond formation. Our work not only addresses a fundamental chemistry question about how high the pressure needs to be for NG elements to form chemical compounds, but it also predicts the intriguing superconductivity of the inter-NG compounds. The required extreme environment for the formation of inter-NG ionic compounds can be found in gas giants, like the planets Jupiter and Saturn, if ultrahigh pressure (>1.5 TPa) is available near the core region. © 2025 Chinese Chemical Society. All rights reserved.