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. SrGeD4/3–x and BaSnD4/3–x 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 d(Ge–D) = 1.521(9) Å and d(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. BaSiD2–x 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 d(Si–D)
= 1.641(5) Å.