LiSrSiOH is synthesized by solid-state reaction of LiH and α-SrSiO. It crystallizes in space group P2/ m ( a = 658.63(4) pm, b = 542.36(3) pm, c = 695.01(4) pm, β = 112.5637(9)°) as proven by X-ray and neutron diffraction, is isotypic to LiSrSiOF, and exhibits isolated SiO tetrahedra. Hydride anions are located in LiSr octahedra, which share faces to form columns, with H-H distances of 271.18(2) pm. NMR, IR, and Raman spectroscopy, density measurements, elemental analysis, and theoretical calculations confirm these results. Despite its hydridic nature, it is stable in air up to 550 K. When doped with europium, it emits bright yellow-green light with an intensity maximum at 560 nm for LiSrEuSiOH. Even after treatment in water for several hours, the solid shows luminescence. The broad emission peak is attributed to the allowed 4f5d → 4f transition of divalent europium. LiSrSiOH is the first silicate hydride, a class of compounds that might have potential as host for luminescent materials.

Metal hydride oxides are an emerging field in solid-state research. While some lanthanide hydride oxides (LnHO) were known, YHO has only been found in thin films so far. Yttrium hydride oxide, YHO, can be synthesized as bulk samples by a reaction of Y 2 O 3 with hydrides (YH 3 , CaH 2 ), by a reaction of YH 3 with CaO, or by a metathesis of YOF with LiH or NaH. X-ray and neutron powder diffraction reveal an anti-LiMgN type structure for YHO (Pnma, a = 7.5367(3) Å, b = 3.7578(2) Å, and c = 5.3249(3) Å) and YDO (Pnma, a = 7.5309(3) Å, b = 3.75349(13) Å, and c = 5.3192(2) Å); in other words, a distorted fluorite type with ordered hydride and oxide anions was observed. Bond lengths (average 2.267 Å (Y−O), 2.352 Å (Y−H), 2.363 Å (Y−D), >2.4 Å (H−H and D−D), >2.6 Å (H−O and D−O), and >2.8 Å (O−O)) and quantummechanical calculations on density functional theory level (band gap 2.8 eV) suggest yttrium hydride oxide to be a semiconductor and to have considerable ionic bonding character. Nonetheless, YHO exhibits a surprising stability in air. An in situ X-ray diffraction experiment shows that decomposition of YHO to Y 2 O 3 starts at only above 500 K and is still not complete after 14 h of heating to a final temperature of 1000 K. YHO hydrolyzes in water very slowly. The inertness of YHO in air is very beneficial for its potential use as a functional material. ■ EXPERIMENTAL SECTIONFour different methods were employed for the synthesis of yttrium hydride oxide YHO (Table 1) using (a) yttria Y 2 O 3 and yttrium hydride YH 3 , (b) yttria and calcium hydride CaH 2 , (c) yttrium hydride and calcium oxide CaO, and (d) yttrium oxide fluoride YOF and alkaline hydride AH (A = Li or Na). Unless otherwise stated, all

Metal hydride oxides are an interesting class of compounds with potential for hydride ion conduction and as host materials for luminescence. SmHO and HoHO were prepared from mixtures of the sesquioxides Ln2O3 and the hydrides LnH2+x at 1173 K as gray powders (Ln=Sm, Ho). They crystallize in a fluorite type crystal structure with disordered anion distribution (Fm3̅m; SmHO: a=5.46953(6) Å, V=163.625(5) Å3; HoHO: a=5.27782(3) Å, V=147.016(2) Å3, based on powder X-ray diffraction) and show stability towards air. Lanthanide-oxygen and -hydrogen distances are 2.36838(3) Å in SmHO and 2.28536(1) Å in HoHO and comparable to those in binary lanthanide oxides and hydrides. Elemental analyses confirm the composition LnHO. Quantum-mechanical calculations show a negative enthalpy for the reaction RE2O3+REH3→3 REHO for all lanthanides and Y, with increasing values for decreasing ionic radii.

The substitution of hydrogen for oxygen atoms in metal oxides provides opportunities for influencing the solid-state properties. Such hydride oxides (or oxyhydrides) are potential functional materials and scarce. Here, we present the synthesis and characterization of holmium hydride oxide with the stoichiometric composition HoHO. It was prepared by the reaction of Ho 2 O 3 with either HoH 3 or CaH 2 as a powder of light-yellow color in sunlight and pink color in artificial light (Alexandrite effect), which is commonly observed for ionic Ho(III) compounds. HoHO crystallizes with an ordered fluorite superstructure (F4̅ 3m, a = 5.27550(13) Å, half-Heusler LiAlSi type), as evidenced by powder X-ray and neutron powder diffraction on both hydride and deuteride and supported by quantum-mechanical calculations. HoHO is the first representative with considerable ionic bonding for this structure type. The thermal stability and inertness toward air are remarkably high for a hydride because it reacts only above 540 K to form Ho 2 O 3 . At 294(1) K and 25(3)% relative humidity, HoHO is stable for at least 3 months. HoHO is paramagnetic with μ eff (Ho 3+ ) = 10.41(2) μ B without any sign of magnetic ordering down to 2 K.

Heteroanionic hydrides offer great possibilities in the design of functional materials. For ternary rare earth hydride oxide REHO, several modifications were reported with indications for a significant phase width with respect to H and O of the cubic representatives. We obtained DyHO and ErHO as well as the thus far elusive LuHO from solid-state reactions of RE2O3 and REH3 or LuH3 with CaO and investigated their crystal structures by neutron and X-ray powder diffraction. While DyHO, ErHO, and LuHO adopted the cubic anion-ordered half-Heusler LiAlSi structure type (F4¯3m, a(DyHO) = 5.30945(10) Å, a(ErHO) = 5.24615(7) Å, a(LuHO) = 5.171591(13) Å), LuHO additionally formed the orthorhombic anti-LiMgN structure type (Pnma; LuHO: a = 7.3493(7) Å, b = 3.6747(4) Å, c = 5.1985(3) Å; LuDO: a = 7.3116(16) Å, b = 3.6492(8) Å, c = 5.2021(7) Å). A comparison of the cubic compounds’ lattice parameters enabled a significant distinction between REHO and REH1+2xO1−x (x < 0 or x > 0). Furthermore, a computational chemistry study revealed the formation of REHO compounds of the smallest rare earth elements to be disfavored in comparison to the sesquioxides, which is why they may only be obtained by mild synthesis conditions.