Beryllium hydride
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| Names | |
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| Other names
Beryllium dihydride
Beryllium hydride Beryllane | |
| Identifiers | |
3D model (JSmol)
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PubChemCID
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CompTox Dashboard(EPA)
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| Properties | |
| BeH2 | |
| Molar mass | 11.03 g mol−1 |
| Appearance | white solid[1] |
| Density | 0.65 g/cm3 |
| Melting point | 250 °C (482 °F; 523 K) decomposes |
| decomposes | |
| Solubility | insoluble indiethyl ether,toluene |
| Thermochemistry | |
| 30.124 J/mol K | |
| Hazards | |
| NIOSH(US health exposure limits): | |
PEL(Permissible)
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TWA 0.002 mg/m3 C 0.005 mg/m3(30 minutes), with a maximum peak of 0.025 mg/m3(as Be)[2] |
REL(Recommended)
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Ca C 0.0005 mg/m3(as Be)[2] |
IDLH(Immediate danger)
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Ca [4 mg/m3(as Be)][2] |
| Related compounds | |
Othercations
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lithium hydride,sodium hydride,magnesium hydride,calcium hydride,boron hydrides,aluminium hydride |
Related compounds
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beryllium fluoride |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Beryllium hydride(systematically namedpoly[beryllane(2)]andberyllium dihydride) is aninorganic compoundwith thechemical formula(BeH
2)n(also written ([BeH
2])norBeH
2). Thisalkaline earth hydrideis a colourless solid that is insoluble in solvents that do not decompose it. Unlike theionically bondedhydridesof the heavierGroup 2elements, beryllium hydride iscovalently bonded[1](three-center two-electron bond).
Synthesis
[edit]Unlike the othergroup 2metals, beryllium does not react with hydrogen.[3]Instead, BeH2is prepared from preformed beryllium(II) compounds. It was first synthesized in 1951 by treatingdimethylberyllium,Be(CH3)2,withlithium aluminium hydride,LiAlH4.[4]
Purer BeH2forms from thepyrolysisof di-tert-butylberyllium, Be(C[CH3]3)2at 210°C.[5]
A route to highly pure samples involves the reaction oftriphenylphosphine,PPh3,withberyllium borohydride,Be(BH4)2:[1]
- Be(BH4)2+ 2 PPh3→ BeH2+ 2 Ph3PBH3
Structure
[edit]Gaseous form
[edit]
Isolated molecules ofBeH
2(sometimes called dihydridoberyllium and written[BeH
2]to emphasize the differences with the solid state) are only stable as adilutegas. When condensed, unsolvatedBeH
2will spontaneously autopolymerise.
Free molecular BeH2produced by high-temperature electrical discharge has been confirmed to havelinear geometrywith a Be-H bond length of 133.376 pm. Its hybridization issp.[6]
Condensed Beryllium hydride
[edit]BeH2is usually formed as an amorphous white solid, but ahexagonal crystalline formwith a higher density (~0.78 g/cm3) was reported,[7]prepared by heating amorphous BeH2under pressure, with 0.5-2.5%LiHas a catalyst.
A more recent investigation found that crystalline beryllium hydride has a body-centredorthorhombicunit cell,containing a network of corner-sharing BeH4tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH2.[8]
Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.[9]
Chemical properties
[edit]Reaction with water and acids
[edit]Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such ashydrogen chlorideto formberyllium chloride.[3]
- BeH2+ 2 H2O → Be(OH)2+ 2 H2
- BeH2+ 2 HCl → BeCl2+ 2 H2
Reaction with Lewis bases
[edit]The two-coordinate hydridoberyllium group can accept an electron-pair donatingligand(L) into the molecule by adduction:[10]
- [BeH
2]+ L →[BeH
2L]
Because these reactions are energetically favored, beryllium hydride hasLewis-acidiccharacter.
The reaction withlithium hydride(in which the hydride ion is the Lewis base), forms sequentially LiBeH3andLi2BeH4.[3]The latter contains thetetrahydridoberyllate(2-)anionBeH2−
4.
Beryllium hydride reacts withtrimethylamine,N(CH3)3to form a dimeric adduct with bridging hydrides.[11]However, withdimethylamine,HN(CH3)2it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3,and hydrogen.[3]
References
[edit]- ^abcGreenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 115.ISBN978-0-08-037941-8.
- ^abcNIOSH Pocket Guide to Chemical Hazards."#0054".National Institute for Occupational Safety and Health(NIOSH).
- ^abcdEgon Wiberg, Arnold Frederick Holleman (2001)Inorganic Chemistry,ElsevierISBN0-12-352651-5,p. 1048
- ^Glenn D. Barbaras; Clyde Dillard; A. E. Finholt; Thomas Wartik; K. E. Wilzbach & H. I. Schlesinger (1951). "The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride".Journal of the American Chemical Society.73(10): 4585–4590.doi:10.1021/ja01154a025.
- ^G. E. Coates & F. Glockling (1954). "Di-tert.-butylberyllium and beryllium hydride".Journal of the Chemical Society:2526–2529.doi:10.1039/JR9540002526.
- ^Peter F. Bernath; Alireza Shayesteh; Keith Tereszchuk; Reginald Colin (2002). "The Vibration-Rotation Emission Spectrum of Free BeH2".Science.297(5585): 1323–1324.Bibcode:2002Sci...297.1323B.doi:10.1126/science.1074580.PMID12193780.S2CID40961746.
- ^G. J. Brendel; E. M. Marlett & L. M. Niebylski (1978). "Crystalline beryllium hydride".Inorganic Chemistry.17(12): 3589–3592.doi:10.1021/ic50190a051.
- ^abGordon S. Smith; Quintin C. Johnson; Deane K. Smith; D. E. Cox; Robert L. Snyder; Rong-Sheng Zhou & Allan Zalkin (1988). "The crystal and molecular structure of beryllium hydride".Solid State Communications.67(5): 491–494.Bibcode:1988SSCom..67..491S.doi:10.1016/0038-1098(84)90168-6.
- ^Sujatha Sampath; Kristina M. Lantzky; Chris J. Benmore; Jörg Neuefeind & Joan E. Siewenie (2003). "Structural quantum isotope effects in amorphous beryllium hydride".J. Chem. Phys.119(23): 12499.Bibcode:2003JChPh.11912499S.doi:10.1063/1.1626638.
- ^Sharp, Stephanie B.; Gellene, Gregory I. (23 November 2000). "σ Bond Activation by Cooperative Interaction withns2Atoms: Be +nH
2,n= 1−3 ".The Journal of Physical Chemistry A.104(46): 10951–10957.doi:10.1021/jp002313m. - ^Shepherd Jr., Lawrence H.; Ter Haar, G. L.; Marlett, Everett M. (April 1969). "Amine complexes of beryllium hydride".Inorganic Chemistry.8(4): 976–979.doi:10.1021/ic50074a051.