Hydrides of Alkaline Earth–Tetrel (AeTt) Zintl Phases: Covalent Tt–H Bonds from Silicon to Tin

Zintl phases form hydrides either by incorporating hydride anions (interstitial hydrides) or by covalent bonding of H to the polyanion (polyanionic hydrides), which yields a variety of different compositions and bonding situations. Hydrides (deuterides) of SrGe, BaSi, and BaSn were prepared by hydrogenation (deuteration) of the CrB-type Zintl phases AeTt and characterized by laboratory X-ray, synchrotron, and neutron diffraction, NMR spectroscopy, and quantum-chemical calculations. SrGeD_{4/3–<i>x</i>} and BaSnD_{4/3–<i>x</i>} show condensed boatlike six-membered rings of Tt atoms, formed by joining three of the zigzag chains contained in the Zintl phase. These new polyanionic motifs are terminated by covalently bound H atoms with <i>d</i>(Ge–D) = 1.521(9) Å and <i>d</i>(Sn–D) = 1.858(8) Å. Additional hydride anions are located in Ae₄ tetrahedra; thus, the features of both interstitial hydrides and polyanionic hydrides are represented. BaSiD_2–<i>x</i> retains the zigzag Si chain as in the parent Zintl phase, but in the hydride (deuteride), it is terminated by H (D) atoms, thus forming a linear (SiD) chain with <i>d</i>(Si–D) = 1.641(5) Å