Synthesis and Crystal Structure of BaLaSi2H0.80

The polyanionic compound BaLaSi₂ featuring cis-trans silicon chains takes up hydrogen to form a hydride BaLaSi₂H_0.80. The crystal structure of the parent intermetallic compound is largely retained upon hydrogenation with the same space group type, a unit cell volume increase of 3.29 % and very similar atomic positions in the hydride. Hydrogen could be located in the crystal structure by neutron diffraction on the deuteride. Deuterium atoms occupy a tetrahedral Ba₃La interstitial with 40.6(2) % occupation (Cmcm, a = 464.43(4) pm, b = 1526.7(1) pm, c = 676.30(6) pm). BaLaSi₂H_0.80 is thus an interstitial Zintl phase hydride like LaSiH_1–x, but unlike BaSiH_2–x does not feature any covalent Si–H bonds. Si–Si distances within the polyanion increase upon hydrogenation from 240.1(6) and 242.9(5) pm to 244.7(2) pm and 245.5(2) pm. This is probably due to oxidation of the polyanion by hydrogen, which leads to the formation of hydride ions and the depopulation of the polyanion's antibonding π* states. Interatomic Ba–D [260.9(4) pm, 295.7(5) pm] and La–D distances [241.2(7) pm] are in the typical range of ionic hydrides.