Two Faces of Hydrogen in Yttrium Hydroxyhydride: Y2H3O(OH) – a New Inorganic Chiral System with Hydridic and Protonic Hydrogens

Design of inorganic compounds containing different anions attracts a lot of attention because it affords a great opportunity to develop new functionality across the whole range of material properties. Based on the results of structure-modeling studies of a mixed-anion system, we predicted novel derivatives of oxyhydrides – chiral hydroxyhydrides M<sub>2</sub>H<sub>3</sub>O(OH) (M = Y, Sc, La, and Gd) that are characterized by the coexistence of three anionic species, H<sup>–</sup>, O2<sup> –</sup>, and OH<sup>–</sup> inside the crystal lattice. The materials demonstrate a specific charge ordering, which is connected with the chiral organization of atoms where both the metal cations and the anions are standing in positions that form helical curves spreading along the tetragonal axis. Moreover, the twisting of the H<sup>–</sup> and H<sup>+</sup> sites gives rise to their linking via strong dihydrogen bonds. Unusual structural, electron and optical features caused by the P4<sub>1</sub> crystal structure have been investigated in the Y<sub>2</sub>H<sub>3</sub>O(OH) comprehensive case study.