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

Abstract

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 BaSiH and BaGeH . 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 HSr (HBa ) 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 (Ae=alkaline earth, Tt=tetrel) can be rationalized with the Zintl-Klemm concept according to (Ae ) (TtH )(Tt H )(H ) , where all Tt atoms are three-binding. The non-stoichiometry (SrSiH , x=0.17(2); BaGeH , x=0.10(3)) can be explained by additional π-bonding of the Tt chains.

The Hydrogenation of the Zintl Phase NdGa Studied by in situ Neutron Diffraction

“…The obtained structure shows chemical and structural similarities to SrSiH 5/3– x and BaGeH 5/3– x , which exhibit a sixfold superstructure regarding the CrB‐structure type . Nevertheless, a description in the ordered SrSiH 5/3– x structure type does not lead to satisfactory refinement results.…”

“…Nevertheless, the bonding situation of hydrogen towards Tt and gallium is quite different. Whereas the existence of a covalent Tt –H bond was established,, the Ga–H distance is quite long (ca. 200 pm) and the coordination can be described as trigonal bipyramidal by Nd in the equatorial plane and Ga on the axial positions.…”

“…Figure , D2 position). NdGaH 1.66 is structurally related to AeTt H 1+ x ( x < 1) ( Ae = Ca – Ba, Tt = Si – Sn), in which, however, the Tt –H interactions are clearly covalent , …”

Size Matters: New Zintl Phase Hydrides of REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) with Large and Small Cations

“…Table 4. [11] CaSiH4/3−x 3.89 3.81 1.02 A condensation of the polyanion (a contracted) is always accompanied by a distortion of the tetrahedra containing layer (b expanded) as seen for TmGaD and YGaD as well as for hydrides in the system AeTt (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn) [17]. A more detailed view is possible, when a second lattice parameter ratio is considered like b/c or c/a.…”

“…Rare earth containing compounds offer the opportunity to vary the cation radius while maintaining the valence electron concentration thus enabling the investigation of the crystal chemistry as a function of the ion size. There are many examples for the hydrogenation of compounds with a CrB type structure, e.g., ZrNi or TbNi forming the metallic hydrides ZrNiH x (x = 1-3) and TbNiH 3.3 and the Zintl phases AeTt (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn), LnTt (Ln = La, Nd; Tt = Si, Ge, Sn), and LnGa (Ln = Nd, Gd) [8,10,[16][17][18][19][20][21]. AeTt (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn) form polyanionic hydrides with different hydrogen content and polyanions with different degrees of condensation (chains, ribbons) determined by the atomic radius ratio r Ae /r Tt .…”