Syntheses of the so-called "suboxide" phases Ba21T2O5 (T = Ge, Si, Ga, In, Tl) are achieved only in the presence of hydrogen. The heavy-atom structure of Ba21Ge2O5H24 at room temperature was redetermined by single-crystal X-ray diffraction and found to be primitive trigonal symmetry (P3(1)21 (No. 152), Z = 6, a = 14.4227(5) Angstrom, c = 35.332(3) Angstrom) instead of the previously refined cubic (Fd (3) over bar 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 Ba2+ 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 Ba21Tr2O5Hx, Tr = Ga, In, Tl, are isotypic with the heavy-atom structure of the title phase and presumably contain 22 hydride ions.