Noble gas hydrides: theoretical prediction of the first group of anionic species.

The first group of anionic noble-gas hydrides with the general formula HNgBeO (Ng = Ar, Kr, Xe, Rn) is predicted through MP2, Coupled-Cluster, and Density Functional Theory computations employing correlation-consistent atomic basis sets. We derive that these species are stable with respect to the loss of H, H, BeO, and BeO, but unstable with respect to Ng + HBeO. The energy barriers of the latter process are, however, high enough to suggest the conceivable existence of the heaviest HNgBeO species as metastable in nature. Their stability arises from the interaction of the H moiety with the positively-charged Ng atoms, particularly with the σ-hole ensuing from their ligation to BeO. This actually promotes relatively tight Ng-H bonds featuring a partially-covalent character, whose degree progressively increases when going from HArBeO to HRnBeO. The HNgBeO compounds are also briefly compared with other noble-gas anions observed in the gas phase or isolated in crystal lattices.