Beryllium hydride
 | |
| Names | |
|---|---|
| Other names
Beryllium dihydride Beryllium hydride Beryllane | |
| Identifiers | |
7787-52-2  | |
| ChEBI | CHEBI:33787  |
| ChemSpider | 17215712 |
| Jmol interactive 3D | Image |
| PubChem | 139073 |
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| |
| Properties | |
| BeH2 | |
| Molar mass | 11.03 g mol−1 |
| Appearance | amorphous white solid[1] |
| Density | 0.65 g/cm3 |
| Melting point | 250 °C (482 °F; 523 K) decomposes |
| decomposes | |
| Solubility | insoluble in diethyl ether, toluene |
| Thermochemistry | |
| 30.124 J/mol K | |
| Hazards | |
| US health exposure limits (NIOSH): | |
| PEL (Permissible) |
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) |
Ca C 0.0005 mg/m3 (as Be)[2] |
| IDLH (Immediate danger |
Ca [4 mg/m3 (as Be)][2] |
| Related compounds | |
| Other cations |
lithium hydride, calcium hydride, boron hydrides |
| Related compounds |
beryllium fluoride |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| verify (what is ?) | |
| Infobox references | |
Beryllium hydride (systematically named beryllium dihydride) is an inorganic compound with the chemical formula (BeH
2)n (also written ([BeH
2])n or BeH
2). It is a colourless solid that is insoluble in solvents that do not decompose it.[3] Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded[1] (three-center two-electron bond).
Synthesis
Unlike the other group 2 metals, beryllium does not react with hydrogen.[4] Instead, BeH2 is prepared from preformed beryllium(II) compounds. It was first synthesised in 1951 by treating dimethylberyllium, Be(CH3)2, with lithium aluminium hydride, LiAlH4.[5]
Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C(CH3)3)2 at 210 °C.[6]
A route to highly pure samples involve the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2:[1]
- Be(BH4)2 + 2 PPh3 → 2 Ph3PBH3 + BeH2
Structure
BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g cm−3) was reported,[7] prepared by heating amorphous BeH2 under pressure, with 0.5-2.5% LiH as a catalyst.
A more recent investigation found that crystalline beryllium hydride has a body-centred orthorhombic unit cell, containing a network of corner-sharing BeH4 tetrahedra, 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
Reaction with water and acids
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as hydrogen chloride to form beryllium chloride.[4]
Reaction with Lewis bases
Beryllium hydride reacts with trimethylamine, N(CH3)3 to form a dimeric aduct, with bridging hydrides.[10] However with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3 and hydrogen.[4] The reaction with lithium hydride where the hydride ion is the Lewis base, forms sequentially LiBeH3 and Li2BeH4.[4]
Dihydridoberyllium
Dihydridoberyllium is a related compound with the chemical formula BeH
2 (also written [BeH
2]). It is a gas that cannot persist undiluted. Unsolvated dihydridoberyllium will spontaneously autopolymerise to oligomers. Free molecular BeH2 produced by electrical discharge at high temperature has been confirmed as linear with a Be-H bond length of 133.376 pm.
[11]
Chemical properties
In theory, the two-coordinate hydridoberyllium group (-BeH) in hydridoberylliums such as dihydridoberyllium can accept an electron-pair donating ligand into the molecule by adduction:[12]
- [BeH
2] + L → [BeH
2L]
Because of this acceptance of the electron-pair donating ligand (L), dihydridoberyllium has Lewis-acidic-acidic character. Dihydridoberyllium can accept four two electron-pairs from ligands, as in the case of the tetrahydridoberyllate(2-) anion (BeH2−
4).
References
- 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9., p. 115
- 1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0054". National Institute for Occupational Safety and Health (NIOSH).
- ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- 1 2 3 4 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5, p. 1048
- ↑ Glenn D. Barbaras, Clyde Dillard, A. E. Finholt, Thomas Wartik, K. E. Wilzbach, and H. I. Schlesinger (1951). "The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride". J. Am. Chem. Soc. 73 (10): 4585–4590. doi:10.1021/ja01154a025.
- ↑ G. E. Coates and F. Glockling (1954). "Di-tert.-butylberyllium and beryllium hydride". J. Chem. Soc.: 2526–2529. doi:10.1039/JR9540002526.
- ↑ G. J. Brendel, E. M. Marlett, and L. M. Niebylski (1978). "Crystalline beryllium hydride". Inorg. Chem. 17 (12): 3589–3592. doi:10.1021/ic50190a051.
- ↑ Gordon S. Smith, Quintin C. Johnson, Deane K. Smith, D. E. Cox, Robert L. Snyder, Rong-Sheng Zhou and Allan Zalkin (1988). "The crystal and molecular structure of beryllium hydride". Solid State Communications 67 (5): 491–494. doi:10.1016/0038-1098(84)90168-6.
- ↑ Sujatha Sampath, Kristina M. Lantzky, Chris J. Benmore, Jörg Neuefeind, and Joan E. Siewenie (2003). "Structural quantum isotope effects in amorphous beryllium hydride". J. Chem. Phys. 119 (23): 12499. doi:10.1063/1.1626638.
- ↑ Shepherd Jr., Lawrence H.; Ter Haar, G. L.; Marlett, Everett M. (April 1969). "Amine complexes of beryllium hydride" (PDF). Inorganic Chemistry (American Chemical Society) 8 (4): 976–979. doi:10.1021/ic50074a051. Retrieved 16 October 2013.
- ↑ Peter F. Bernath, Alireza Shayesteh, Keith Tereszchuk, Reginald Colin (2002). "The Vibration-Rotation Emission Spectrum of Free BeH2". Science 297 (5585): 1323–1324. doi:10.1126/science.1074580. PMID 12193780.
- ↑ Sharp, Stephanie B.; Gellene, Gregory I. (23 November 2000). "σ Bond Activation by Cooperative Interaction with ns2 Atoms: Be + n H
2, n = 1−3". The Journal of Physical Chemistry A (ACS Publications) 104 (46): 10951–10957. doi:10.1021/jp002313m.
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