Beryllium hydride
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| Names | |
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| Other names
Beryllium dihydride
Beryllium hydride Beryllane |
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| Identifiers | |
7787-52-2  |
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| ChEBI | CHEBI:33787  |
| ChemSpider | 17215712 |
| Jmol 3D model | Interactive 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 | |
| Vapor pressure | {{{value}}} |
| Related compounds | |
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Other cations
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lithium hydride, calcium hydride, boron hydrides |
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Related compounds
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beryllium fluoride |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 verify (what is ?) |
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| 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.[2] Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded[1] (three-center two-electron bond).
Contents
Synthesis
Unlike the other group 2 metals, beryllium does not react with hydrogen.[3] 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.[4]
Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C(CH3)3)2 at 210 °C.[5]
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,[6] 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.[7]
Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.[8]
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.[3]
Reaction with Lewis bases
Beryllium hydride reacts with trimethylamine, N(CH3)3 to form a dimeric aduct, with bridging hydrides.[9] However with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3 and hydrogen.[3] The reaction with lithium hydride where the hydride ion is the Lewis base, forms sequentially LiBeH3 and Li2BeH4.[3]
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. [10]
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:[11]
- [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
- ↑ 1.0 1.1 1.2 Lua error in package.lua at line 80: module 'strict' not found., p. 115
- ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- ↑ 3.0 3.1 3.2 3.3 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5, p. 1048
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
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