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 elementhydrogen bonds in the solid state. The hydrogenation of SrSi, BaSi and BaGe yields the hydrides SrSiH5/3-x, BaSiH5/3-x and BaGeH5/3-x. The crystal structures show a six-fold 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, where hydrogen atoms are covalently bound to silicon and germanium. The idealized formulae AeTtH5/3 (Ae = alkaline earth, Tt = tetrel) can be rationalized with the Zintl-Klemm concept according to (Ae2+)3(TtH-)(Tt2H2-)(H-)3, where all Tt atoms are three-binding. The non-stoichiometry (SrSiH5/3-x, x = 0.17(2); BaGeH5/3-x, x = 0.10(3)) can be explained by additional π-bonding of the Tt chains