Ba₂₁Ge₂O₅H₂₄ and Related Phases. A Corrected Structure Type and Composition for a Zintl Phase Stabilized by Hydrogen

Abstract

Syntheses of the so-called “suboxide” phases Ba 21 T 2 O 5 (T = Ge, Si, Ga, In, Tl) are achieved only in the presence of hydrogen. The heavy-atom structure of Ba 21 Ge 2 O 5 H 24 at room temperature was redetermined by single-crystal X-ray diffraction and found to be primitive trigonal symmetry ( P 3 1 21 (No. 152), Z = 6, a = 14.4227(5) Å, c = 35.332(3) Å) instead of the previously refined cubic ( Fd 3̄ m ) result. The change greatly improves the heavy-atom parameters. Twenty-four independent deuterium atoms have also been located by time-of-flight neutron diffraction. The structure contains Ba 2+ cations, and three different types of monatomic anions, corresponding to the oxidation states (Ba +2 ) 21 (Ge -4 ) 2 (O -2 ) 5 (H - ) 24 . The deuterium atoms occupy tetrahedral, square-pyramidal, and octahedral barium interstices while the oxide anions lie in nearly regular octahedral barium polyhedra. The germanide anions are surrounded by 12 barium atoms in a distorted icosahedral configuration. Property measurements show that Ba 21 Ge 2 O 5 H 24 is diamagnetic and is a semiconductor (or insulator). The analogues Ba 21 Tr 2 O 5 H x, Tr = Ga, In, Tl, are isotypic with the heavy-atom structure of the title phase and presumably contain 22 hydride ions.