• Source: Beryllium hydride

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).




Synthesis


Unlike the other group 2 metals, beryllium does not react with hydrogen. 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.
Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C[CH3]3)2 at 210°C.
A route to highly pure samples involves the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2:

Be(BH4)2 + 2 PPh3 → BeH2 + 2 Ph3PBH3




Structure






= Gaseous form

=

Isolated molecules of BeH2 (sometimes called dihydridoberyllium and written [BeH2] to emphasize the differences with the solid state) are only stable as a dilute gas. When condensed, unsolvated BeH2 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.




= Condensed Beryllium hydride

=
BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm3) 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.




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.

BeH2 + 2 H2O → Be(OH)2 + 2 H2
BeH2 + 2 HCl → BeCl2 + 2 H2




= Reaction with Lewis bases

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The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction:

[BeH2] + L → [BeH2L]
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. 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. However, with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3, and hydrogen.




References

Kata Kunci Pencarian:

• Berilium
• Unsur golongan 3
• Bilangan oksidasi
• Kamus rumus kimia
• Aktinium
• Beryllium hydride
• Magnesium hydride
• Beryllium
• List of inorganic compounds
• Strontium hydride
• Beryllium borohydride
• Calcium hydride
• List of named alloys
• Binary compounds of hydrogen
• Alkaline earth metal