Structural and Electronic Flexibility in Hydrides of Zintl Phases with Tetrel-Hydrogen and Tetrel-Tetrel Bonds

The hydrogenation of Zintl phases enables the formation of new structural entities with main-group-element-hydrogen bonds in the solid state. The hydrogenation of SrSi, BaSi, and BaGe yields the hydrides SrSiH_5/3-x, BaSiH_5/3-x and BaGeH_5/3-x . The crystal structures show a sixfold superstructure compared to the parent Zintl phase and were solved by a combination of X-ray, neutron, and electron diffraction and the aid of DFT calculations. Layers of connected HSr₄ (HBa₄ ) tetrahedra containing hydride ions alternate with layers of infinite single- and double-chain polyanions, in which hydrogen atoms are covalently bound to silicon and germanium. The idealized formulae AeTtH_5/3 (Ae=alkaline earth, Tt=tetrel) can be rationalized with the Zintl-Klemm concept according to (Ae²⁺ )₃ (TtH^- )(Tt₂ H^2- )(H^- )₃ , where all Tt atoms are three-binding. The non-stoichiometry (SrSiH_5/3-x , x=0.17(2); BaGeH_5/3-x , x=0.10(3)) can be explained by additional π-bonding of the Tt chains.