A metastable He-O bond inside a ferroelectric molecular cavity: (HeO)(LiF)2.

Elemental helium is a prototypical noble gas and its atom sets the records for many physicochemical properties. With its two electrons in the closed 1s shell, He is the smallest, the least polarizable, the most difficult to ionize, the hardest (in Pearson's sense) and the most electronegative atom known. Helium gas is considered to be as close to an 'ideal gas' as possible and used as a standard of compressibility and pressure. As a consequence of its closed-shell electronic configuration, helium also exhibits chemical inertness: non-charged species which contain chemically bound helium have not been synthesized to date. Here we are able to predict, using quantum mechanical methods, a small neutral molecule, (HeO)(LiF)(2), which contains a helium atom chemically bound to oxygen. The molecule is planar with the polarized He(δ+)O(δ-) unit embedded anti-parallel in-between two co-aligned LiF dipoles. We calculate its selected physicochemical properties as well as suggest possible decomposition and synthesis pathways. Successful preparation of neutral species, (HeO)(LiF)(2) or related molecules, would break down the paradigm of helium's inertness.