3D model (JSmol)
|Molar mass||11.03 g mol−1|
|Melting point||250 °C (482 °F; 523 K) decomposes|
|Solubility||insoluble in diethyl ether, toluene|
Heat capacity (C)
|30.124 J/mol K|
|NIOSH (US health exposure limits):|
|TWA 0.002 mg/m3|
C 0.005 mg/m3 (30 minutes), with a maximum peak of 0.025 mg/m3 (as Be)
|Ca C 0.0005 mg/m3 (as Be)|
IDLH (Immediate danger)
|Ca [4 mg/m3 (as Be)]|
|lithium hydride, calcium hydride, boron hydrides|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an inorganic compound with the chemical formula (BeH2)n (also written ([BeH2])n or BeH2). 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 (three-center two-electron bond).
Unlike the other group 2 metals, beryllium does not react with hydrogen. 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.
- Be(BH4)2 + 2 PPh3 → BeH2 + 2 Ph3PBH3
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, 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.
Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.
Reaction with water and acids
- BeH2 + 2 H2O → Be(OH)2 + 2 H2
- BeH2 + 2 HCl → BeCl2 + 2 H2
Reaction with Lewis bases
Beryllium hydride reacts with trimethylamine, N(CH3)3 to form a dimeric adduct, with bridging hydrides. However, with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3 and hydrogen. The reaction with lithium hydride where the hydride ion is the Lewis base, forms sequentially LiBeH3 and Li2BeH4.
Dihydridoberyllium is a related compound with the chemical formula BeH2 (also written [BeH2]). 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. Its hybridisation is sp. 
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:
- [BeH2] + L → [BeH2L]
Because of this acceptance of the electron-pair donating ligand (L), dihydridoberyllium has Lewis-acidic character. Dihydridoberyllium can accept two electron pairs from ligands, as in the case of the tetrahydridoberyllate(2-) anion (BeH2−4).
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- 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. doi:10.1063/1.1626638. Bibcode: 2003JChPh.11912499S.
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- Sharp, Stephanie B.; Gellene, Gregory I. (23 November 2000). "σ Bond Activation by Cooperative Interaction with ns2 Atoms: Be + n H2, n = 1−3". The Journal of Physical Chemistry A 104 (46): 10951–10957. doi:10.1021/jp002313m.
Original source: https://en.wikipedia.org/wiki/Beryllium hydride. Read more