Oxyhydride

An oxyhydride is a mixed anion compound containing both oxide O2− and hydride ions H−. These compounds may be unexpected as the hydrogen and oxygen could be expected to react to form water. But if the metals making up the anions are electropositive enough, and the conditions are reducing enough, solid materials can be made that combine hydrogen and oxygen in the negative ion role.

Production

The first oxyhydride to be discovered was lanthanum oxyhydride, a 1982 discovery. It was made by heating lanthanum oxide in an atmosphere of hydrogen at 900 °C.[1] However heating transition metal oxides with hydrogen, usually results in reduction to the metal.[1]

Topochemical synthesis retains the basic structure of the parent compound, and only does the minimum rearrangements of atoms to convert to the final product.[1] Topotactic reactions retain the original crystal symmetry.[1] Reactions at lower temperatures do not distorub the existing structure. Oxyhydrides in a topochemical synthesis can be produced by heating oxides with sodium hydride NaH or calcium hydride CaH2 at temperatures from 200–600 °C.[2] TiH2 or LiH can also be used as an agent to introduce hydride.[1] If calcium hydroxide or sodium hydroxide is formed, it might be able to be washed away.[1] However for some starting oxides, this kind of hydride reduction might just yield an oxygen deficient oxide.[1]

Reactions under hot high pressure hydrogen can result from heating hydrides with oxides. A suitable seal for the lid on the container is required, and one such substance is sodium chloride.[3]

Oxyhydrides all contain an alkali, alkaline earth, or rare earth metal, which are needed in order to put electronic charge on hydrogen.[3]

Properties

The hydrogen bonding in oxyhydrides can be covalent, metallic, and ionic bonding, dependent on the metals present in the compound.[3] Oxyhydrides lose their hydrogen less than the pure metal hydrides.[2] The hydrogen in oxyhydrides is much more exchangeable. For example oxynitrides can be made at much lower temperatures by heating the oxyhydride in ammonia or nitrogen gas (say around 400 °C rather than 900 °C required for an oxide)[2] Acidic attack can replace the hydrogen, for example moderate heating in hydrogen fluoride yields compounds containing oxide, fluoride and hydride ions. (oxyfluorohydride[4]) The hydrogen is more thermolabile, and can be lost by heating yielding a reduced valence metal compound.[2]

Changing the ratio of hydrogen and oxygen can modify electrical or magnetic properties. Then band gap can be altered.[2] The hydride atom can be mobile in a compound undergoing electron coupled hydride transfer.[3] The hydride ion is highly polarisable, so it presence raised the dielectric constant and refractive index.[3]

Some oxyhydrides have photocatalytic capability. For example BaTiO2.5H0.5 can function as a catalyst for ammonia production from hydrogen and nitrogen.[2]

The hydride ion is quite variable in size, ranging from 130 to 153 pm.[3]

The hydride ion actually does not only have a −1 charge, but will have a charge dependent on its environment, so it is often written as Hδ−.[3] In oxyhydrides, the hydride ion is much more compressible than the other atoms in compounds.[3] Hydride is the only anion with no π-orbital, so if it is incorporated into a compound, it acts as a π-blocker, reducing dimensionality of the solid.[3]

Oxyhydride structures with heavy metals cannot be properly studied with X-ray diffraction, as hydrogen hardly has any effect on X-rays. Neutron diffraction can be used to observe hydrogen, but not if there are heavy neutron absorbers like Eu, Sm, Gd, Dy in the material.[1]

List
Formula Structure Space group Unit cell Comments Reference
La2LiHO3 [3]
La0.6Sr1.4LiH1.6O2 H− conductor [3]
SrVO2H [2]
Sr2VO3H [2]
Sr3V2O5H2 [2]
LaSr3NiRuO4H4 [2]
LaSrMnO3.3H0.7 high pressure fabrication [2]
SrCrO2H cubic produced under 5GPa 1000 °C [2]
LaSrCoO3H0.7 insulator [2]
Sr3Co2O4.33H0.84 insulator [2]
EuTiO3−xHx (x ≤ 0.6) Conducting; H in disordered position [2]
CaTiO3−xHx (x ≤ 0.6) Conducting; H in disordered position [2]
Sr21Si2O5H14 cubic [5]
SrTiO3−xHx (x ≤ 0.6) Conducting; H in disordered position [2]
Ba3AlO4H orthorhombic Pnma Z=4,a=10.4911,b=8.1518,c=7.2399 [6]
BaTiO3−xHx (x ≤ 0.6) Conducting; H in disordered position [2]
BaVO3−xHx (x = .3) 5 GPa hexagonal, 7GPa cubic [2]
Ba21Zn2O5H12 cubic a = 20.417 [5]
Ba21Cd2O5H12 cubic a=20.633 [5]
Ba21Hg2O5H12 cubic a=20.507 [5]
Ba21In2O5H12 cubic a=20.607 [5]
Ba21Tl2O5H12 cubic a=20.68 [5]
Ba21Si2O5H14 cubic a=20.336 [5]
Ba21Ge2O5H14 cubic a=20.356 [5]
Ba21Sn2O5H14 cubic a=20.532 [5]
Ba21Pb2O5H14 cubic a=20.597 [5]
Ba21As2O5H16 cubic a=20.230 [5]
Ba21Sb2O5H16 cubic a=20.419 [5]
Ba21Bi2O5H16 cubic a=20.459 [5]
YOxHy photochromic; band gap 2.6 eV [7]
LaHO [8]
CeHO [8]
PrHO [8]
NdHO P4/nmm a=7.8480, c=5.5601 V=342.46 [8]
GdHO Fmm a = 5.38450 [9]
CeNiHZOY Catalyse ethanol to H2 [10]
BaScO2H Cubic Pm3̅m a=4.1518 [11]
Ba2ScHO3 H− conductor [12]
Mg2AlNiXHZOY [13]
Sr2LiH3O ionic conductor [14]
Zr3V3OD5 [1]
Zr5Al3OH5 [1]
Ba3AlO4H [1]
Ba21Si2O5H24 Zintl phase [1]
Ba21Ge2O5H24 Zintl phase [1]
Ba21Ga2O5H24 Zintl phase [1]
Ba21In2O5H24 Zintl phase [1]
Ba21Tl2O5H24 Zintl phase [1]

Three or more anions
Formula Structure Space group Unit cell Comments Reference
LiEu2HOCl2 orthorhombic Cmcm a = 1492.30(11) pm, b = 570.12(4) pm, c = 1143.71(8) pm, Z = 8 yellow [15]

References
  1. Kobayashi, Yoji; Hernandez, Olivier; Tassel, Cédric; Kageyama, Hiroshi (16 November 2017). "New chemistry of transition metal oxyhydrides". Science and Technology of Advanced Materials. 18 (1): 905–918. Bibcode:2017STAdM..18..905K. doi:10.1080/14686996.2017.1394776. PMC 5784496. PMID 29383042.
  2. Kageyama, Hiroshi; Yajima, Takeshi; Tsujimoto, Yoshihiro; Yamamoto, Takafumi; Tassel, Cedric; Kobayashi, Yoji (15 August 2019). "Exploring Structures and Properties through Anion Chemistry". Bulletin of the Chemical Society of Japan. 92 (8): 1349–1357. doi:10.1246/bcsj.20190095.
  3. Kageyama, Hiroshi; Hayashi, Katsuro; Maeda, Kazuhiko; Attfield, J. Paul; Hiroi, Zenji; Rondinelli, James M.; Poeppelmeier, Kenneth R. (22 February 2018). "Expanding frontiers in materials chemistry and physics with multiple anions". Nature Communications. 9 (1): 772. Bibcode:2018NatCo...9..772K. doi:10.1038/s41467-018-02838-4. PMC 5823932. PMID 29472526.
  4. KAMIGAITO, Osami (2000). "Density of Compound Oxides". Journal of the Ceramic Society of Japan. 108 (1262): 944–947. doi:10.2109/jcersj.108.1262_944.
  5. Jehle, Michael; Hoffmann, Anke; Kohlmann, Holger; Scherer, Harald; Röhr, Caroline (February 2015). "The 'sub' metallide oxide hydrides Sr 21 Si 2 O 5 H 12 + x and Ba 21 M 2 O 5 H 12 + x ( M = Zn, Cd, Hg, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi)". Journal of Alloys and Compounds. 623: 164–177. doi:10.1016/j.jallcom.2014.09.228.
  6. Huang, Baoquan; Corbett, John D. (December 1998). "Ba3AlO4H: Synthesis and Structure of a New Hydrogen-Stabilized Phase". Journal of Solid State Chemistry. 141 (2): 570–575. Bibcode:1998JSSCh.141..570H. doi:10.1006/jssc.1998.8022.
  7. Plokker, M.P.; Eijt, S.W.H.; Naziris, F.; Schut, H.; Nafezarefi, F.; Schreuders, H.; Cornelius, S.; Dam, B. (April 2018). "Electronic structure and vacancy formation in photochromic yttrium oxy-hydride thin films studied by positron annihilation". Solar Energy Materials and Solar Cells. 177: 97–105. doi:10.1016/j.solmat.2017.03.011.
  8. Widerøe, Marius; Fjellvåg, Helmer; Norby, Truls; Willy Poulsen, Finn; Willestofte Berg, Rolf (July 2011). "NdHO, a novel oxyhydride". Journal of Solid State Chemistry. 184 (7): 1890–1894. Bibcode:2011JSSCh.184.1890W. doi:10.1016/j.jssc.2011.05.025.
  9. Ueda, Jumpei; Matsuishi, Satoru; Tokunaga, Takayuki; Tanabe, Setsuhisa (2018). "Preparation, electronic structure of gadolinium oxyhydride and low-energy 5d excitation band for green luminescence of doped Tb 3+ ions". Journal of Materials Chemistry C. 6 (28): 7541–7548. doi:10.1039/C8TC01682H. ISSN 2050-7526.
  10. Pirez, Cyril; Capron, Mickaël; Jobic, Hervé; Dumeignil, Franck; Jalowiecki-Duhamel, Louise (2011-10-17). "Highly Efficient and Stable CeNiHZOY Nano-Oxyhydride Catalyst for H2 Production from Ethanol at Room Temperature". Angewandte Chemie International Edition. 50 (43): 10193–10197. doi:10.1002/anie.201102617. PMID 21990250.
  11. Goto, Yoshihiro; Tassel, Cédric; Noda, Yasuto; Hernandez, Olivier; Pickard, Chris J.; Green, Mark A.; Sakaebe, Hikari; Taguchi, Noboru; Uchimoto, Yoshiharu; Kobayashi, Yoji; Kageyama, Hiroshi (May 2017). "Pressure-Stabilized Cubic Perovskite Oxyhydride BaScO 2 H". Inorganic Chemistry. 56 (9): 4840–4845. doi:10.1021/acs.inorgchem.6b02834. ISSN 0020-1669. PMID 28398729.
  12. Takeiri, Fumitaka; Watanabe, Akihiro; Kuwabara, Akihide; Nawaz, Haq; Ayu, Nur Ika Puji; Yonemura, Masao; Kanno, Ryoji; Kobayashi, Genki (20 February 2019). "Ba2 ScHO3 : H- Conductive Layered Oxyhydride with H- Site Selectivity". Inorganic Chemistry. 58 (7): 4431–4436. doi:10.1021/acs.inorgchem.8b03593. PMID 30784265.
  13. Fang, Wenhao; Romani, Yann; Wei, Yaqian; Jiménez-Ruiz, Mónica; Jobic, Hervé; Paul, Sébastien; Jalowiecki-Duhamel, Louise (September 2018). "Steam reforming and oxidative steam reforming for hydrogen production from bioethanol over Mg2AlNiXHZOY nano-oxyhydride catalysts". International Journal of Hydrogen Energy. 43 (37): 17643–17655. doi:10.1016/j.ijhydene.2018.07.103.
  14. Kobayashi, G.; Hinuma, Y.; Matsuoka, S.; Watanabe, A.; Iqbal, M.; Hirayama, M.; Yonemura, M.; Kamiyama, T.; Tanaka, I.; Kanno, R. (17 March 2016). "Pure H- conduction in oxyhydrides". Science. 351 (6279): 1314–1317. Bibcode:2016Sci...351.1314K. doi:10.1126/science.aac9185. PMID 26989251.
  15. Rudolph, Daniel; Enseling, David; Jüstel, Thomas; Schleid, Thomas (17 November 2017). "Crystal Structure and Luminescence Properties of the First Hydride Oxide Chloride with Divalent Europium: LiEu2HOCl2". Zeitschrift für anorganische und allgemeine Chemie. 643 (21): 1525–1530. doi:10.1002/zaac.201700224.
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