Magnesium hydride

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Magnesium hydride
Magnesium-hydride-unit-cell-3D-balls.png
Magnesium-hydride-xtal-3D-ionic-B.png
Names
IUPAC name
Magnesium hydride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.824 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-705-3
PubChem CID
UNII
  • InChI=1S/Mg.2H Yes check.svgY
    Key: RSHAOIXHUHAZPM-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/Mg.2H/rH2Mg/h1H2
    Key: RSHAOIXHUHAZPM-HZAFDXBCAG
  • [MgH2]
Properties
MgH2
Molar mass 26.3209 g/mol
Appearancewhite crystals
Density 1.45 g/cm3
Melting point 327 °C (621 °F; 600 K) decomposes
decomposes
Solubility insoluble in ether
Structure
tetragonal
Thermochemistry
35.4 J/mol K
Std molar
entropy (S⦵298)
31.1 J/mol K
-75.2 kJ/mol
-35.9 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 pyrophoric [1]
Related compounds
Other cations
Beryllium hydride
Calcium hydride
Strontium hydride
Barium hydride
Magnesium monohydride Mg4H6
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium. [2]

Contents

Preparation

In 1951 preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500 °C) with MgI2 catalyst: [3]

Mg + H2 → MgH2

Lower temperature production from Mg and H2 using nanocrystalline Mg produced in ball mills has been investigated. [4] Other preparations include:

Mg(anthracene) + H2 → MgH2

Structure and bonding

The room temperature form α-MgH2 has a rutile structure. [7] There are at least four high pressure forms: γ-MgH2 with α-PbO2 structure, [8] cubic β-MgH2 with Pa-3 space group, [9] orthorhombic HP1 with Pbc21 space group and orthorhombic HP2 with Pnma space group. [10] Additionally a non stoichiometric MgH(2-δ) has been characterised, but this appears to exist only for very small particles [11]
(bulk MgH2 is essentially stoichiometric, as it can only accommodate very low concentrations of H vacancies [12] ).

The bonding in the rutile form is sometimes described as being partially covalent in nature rather than purely ionic; [13] charge density determination by synchrotron x-ray diffraction indicates that the magnesium atom is fully ionised and spherical in shape and the hydride ion is elongated. [14] Molecular forms of magnesium hydride, MgH, MgH2, Mg2H, Mg2H2, Mg2H3, and Mg2H4 molecules identified by their vibrational spectra have been found in matrix isolated samples at below 10 K, formed following laser ablation of magnesium in the presence of hydrogen. [15] The Mg2H4 molecule has a bridged structure analogous to dimeric aluminium hydride, Al2H6. [15]

Reactions

MgH2 readily reacts with water to form hydrogen gas:

MgH2 + 2 H2O → 2 H2 + Mg(OH)2

At 287 °C it decomposes to produce H2 at 1 bar pressure. [16] The high temperature required is seen as a limitation in the use of MgH2 as a reversible hydrogen storage medium: [17]

MgH2 → Mg + H2

Related Research Articles

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Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li[AlH4] or LiAlH4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.

<span class="mw-page-title-main">Sodium borohydride</span> Chemical compound

Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds application in papermaking and dye industries. It is also used as a reagent in organic synthesis.

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<span class="mw-page-title-main">Hydrogen storage</span> Methods of storing hydrogen for later use

Several methods exist for storing hydrogen. These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H2 upon demand. While large amounts of hydrogen are produced by various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia. For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs. Interest in using hydrogen for on-board storage of energy in zero-emissions vehicles is motivating the development of new methods of storage, more adapted to this new application. The overarching challenge is the very low boiling point of H2: it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy.

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<span class="mw-page-title-main">Lithium borohydride</span> Chemical compound

Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.

<span class="mw-page-title-main">Sodium aluminium hydride</span> Chemical compound

Sodium aluminium hydride or sodium alanate is an inorganic compound with the chemical formula NaAlH4. It is a white pyrophoric solid that dissolves in tetrahydrofuran (THF), but not in diethyl ether or hydrocarbons. It has been evaluated as an agent for the reversible storage of hydrogen and it is used as a reagent for the chemical synthesis of organic compounds. Similar to lithium aluminium hydride, it is a salt consisting of separated sodium cations and tetrahedral AlH−
4 anions.

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2)
n. It is a solid, known only as a thermally unstable, insoluble white powder.

<span class="mw-page-title-main">Lithium imide</span> Chemical compound

Lithium imide is an inorganic compound with the chemical formula Li2NH. This white solid can be formed by a reaction between lithium amide and lithium hydride.

<span class="mw-page-title-main">Iron hydride</span> Index of articles associated with the same name

An iron hydride is a chemical system which contains iron and hydrogen in some associated form.

Magnesium nickel hydride is the chemical compound Mg2NiH4. It contains 3.6% by weight of hydrogen and has been studied as a potential hydrogen storage medium.

Chromium hydrides are compounds of chromium and hydrogen, and possibly other elements. Intermetallic compounds with not-quite-stoichometric quantities of hydrogen exist, as well as highly reactive molecules. When present at low concentrations, hydrogen and certain other elements alloyed with chromium act as softening agents that enables the movement of dislocations that otherwise not occur in the crystal lattices of chromium atoms.

Maximilian Fichtner is professor for Solid State Chemistry at the Ulm University and Executive Director of the Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU).

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Carbohydrides are solid compounds in one phase composed of a metal with carbon and hydrogen in the form of carbide and hydride ions. The term carbohydride can also refer to a hydrocarbon.

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Dibutylmagnesium is an organometallic chemical compound of magnesium. Its chemical formula is C
8H
18Mg. Dibutylmagnesium is a chemical compound from the group of organomagnesium compounds. The pure substance is a waxy solid. Commercially, it is marketed as solution in heptane.

Fluorohydride salts are ionic compounds containing a mixture of fluoride and hydride anions, generally with strongly electropositive metal cations. Unlike other types of mixed hydrides such as oxyhydrides, fluorohydride salts are typically solid solutions because of the similar sizes and identical charges of fluoride and hydride ions.

References

  1. 1 2 Michalczyk, Michael J (1992). "Synthesis of magnesium hydride by the reaction of phenylsilane and dibutylmagnesium". Organometallics. 11 (6): 2307–2309. doi:10.1021/om00042a055.
  2. ↑ Bogdanovic, Borislav (1985). "Catalytic Synthesis of Organolithium and Organomagnesium Compounds and of Lithium and Magnesium Hydrides - Applications in Organic Synthesis and Hydrogen Storage". Angewandte Chemie International Edition in English. 24 (4): 262–273. doi:10.1002/anie.198502621.
  3. ↑ Egon Wiberg; Heinz Goeltzer; Richard Bauer (1951). "Synthese von Magnesiumhydrid aus den Elementen" [Synthesis of Magnesium Hydride from the Elements](PDF). Zeitschrift für Naturforschung B (in German). 6b: 394.
  4. ↑ Zaluska, A; Zaluski, L; Ström–Olsen, J.O (1999). "Nanocrystalline magnesium for hydrogen storage". Journal of Alloys and Compounds . 288 (1–2): 217–225. doi:10.1016/S0925-8388(99)00073-0.
  5. ↑ Bogdanović, Borislav; Liao, Shih-Tsien; Schwickardi, Manfred; Sikorsky, Peter; Spliethoff, Bernd (1980). "Catalytic Synthesis of Magnesium Hydride under Mild Conditions". Angewandte Chemie International Edition in English. 19 (10): 818. doi:10.1002/anie.198008181.
  6. ↑ Barbaras, Glenn D; Dillard, Clyde; Finholt, A. E; Wartik, Thomas; Wilzbach, K. E; Schlesinger, H. I (1951). "The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride1". Journal of the American Chemical Society. 73 (10): 4585. doi:10.1021/ja01154a025.
  7. ↑ Zachariasen, W. H; Holley, C. E; Stamper, J. F (1963). "Neutron diffraction study of magnesium deuteride". Acta Crystallographica. 16 (5): 352. doi: 10.1107/S0365110X63000967 .
  8. ↑ Bortz, M; Bertheville, B; Böttger, G; Yvon, K (1999). "Structure of the high pressure phase γ-MgH2 by neutron powder diffraction". Journal of Alloys and Compounds. 287 (1–2): L4–L6. doi:10.1016/S0925-8388(99)00028-6.
  9. ↑ Vajeeston, P; Ravindran, P; Hauback, B. C; Fjellvåg, H; Kjekshus, A; Furuseth, S; Hanfland, M (2006). "Structural stability and pressure-induced phase transitions inMgH2". Physical Review B. 73 (22): 224102. Bibcode:2006PhRvB..73v4102V. doi:10.1103/PhysRevB.73.224102.
  10. ↑ Moriwaki, Toru; Akahama, Yuichi; Kawamura, Haruki; Nakano, Satoshi; Takemura, Kenichi (2006). "Structural Phase Transition of Rutile-Type MgH2at High Pressures". Journal of the Physical Society of Japan. 75 (7): 074603. Bibcode:2006JPSJ...75g4603M. doi:10.1143/JPSJ.75.074603.
  11. ↑ Schimmel, H. Gijs; Huot, Jacques; Chapon, Laurent C; Tichelaar, Frans D; Mulder, Fokko M (2005). "Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium". Journal of the American Chemical Society. 127 (41): 14348–54. doi:10.1021/ja051508a. PMID   16218629.
  12. ↑ Grau-Crespo, R.; K. C. Smith; T. S. Fisher; N. H. de Leeuw; U. V. Waghmare (2009). "Thermodynamics of hydrogen vacancies in MgH2 from first-principles calculations and grand-canonical statistical mechanics". Physical Review B. 80 (17): 174117. arXiv: 0910.4331 . Bibcode:2009PhRvB..80q4117G. doi:10.1103/PhysRevB.80.174117. S2CID   32342746.
  13. ↑ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN   0-471-19957-5
  14. ↑ Noritake, T; Towata, S; Aoki, M; Seno, Y; Hirose, Y; Nishibori, E; Takata, M; Sakata, M (2003). "Charge density measurement in MgH2 by synchrotron X-ray diffraction". Journal of Alloys and Compounds. 356–357: 84–86. doi:10.1016/S0925-8388(03)00104-X.
  15. 1 2 Wang, Xuefeng; Andrews, Lester (2004). "Infrared Spectra of Magnesium Hydride Molecules, Complexes, and Solid Magnesium Dihydride". The Journal of Physical Chemistry A. 108 (52): 11511. Bibcode:2004JPCA..10811511W. doi:10.1021/jp046410h.
  16. ↑ McAuliffe, T. R. (1980). Hydrogen and Energy (illustrated ed.). Springer. p. 65. ISBN   978-1-349-02635-7. Extract of page 65
  17. ↑ Schlapbach, Louis; Züttel, Andreas (2001). "Hydrogen-storage materials for mobile applications" (PDF). Nature. 414 (6861): 353–8. Bibcode:2001Natur.414..353S. doi:10.1038/35104634. PMID   11713542. S2CID   3025203.
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