Names | |
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Other names
Beryllium dihydride
Beryllium hydride Beryllane | |
Identifiers | |
3D model (
JSmol)
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ChEBI | |
ChemSpider | |
PubChem
CID
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UNII | |
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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 in diethyl ether, toluene |
Thermochemistry | |
Heat capacity (C)
|
30.124 J/mol K |
Hazards | |
NIOSH (US health exposure limits): | |
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)
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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, sodium hydride, magnesium hydride, calcium hydride, boron hydrides, aluminium hydride |
Related compounds
|
beryllium fluoride |
Except where otherwise noted, data are given for materials in their
standard state (at 25 °C [77 °F], 100 kPa).
|
Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an
inorganic compound with the
chemical formula (BeH
2)n (also written ([BeH
2)n or BeH
2). This
alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the
ionically bonded
hydrides of the heavier
Group 2 elements, beryllium hydride is
covalently bonded
[1] (
three-center two-electron bond).
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 synthesized 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[CH33)2 at 210°C. [5]
A route to highly pure samples involves the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2: [1]
Isolated molecules of BeH
2 (sometimes called dihydridoberyllium and written [BeH
2 to emphasize the differences with the solid state) are only stable as a
dilute gas. When condensed, unsolvated BeH
2 will spontaneously autopolymerise.
Free molecular BeH2 produced by high-temperature electrical discharge has been confirmed to have linear geometry with a Be-H bond length of 133.376 pm. Its hybridization is sp. [6]
BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm3) 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]
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as hydrogen chloride to form beryllium chloride. [3]
The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction: [10]
Because these reactions are energetically favored, beryllium hydride has Lewis-acidic character.
The reaction with
lithium hydride (in which the hydride ion is the Lewis base), forms sequentially LiBeH3 and
Li2BeH4.
[3] The latter contains the
tetrahydridoberyllate(2-) anion BeH2−
4.
Beryllium hydride reacts with trimethylamine, N(CH3)3 to form a dimeric adduct with bridging hydrides. [11] However, with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)23, and hydrogen. [3]