Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an inorganic compound with the chemical formula (also written or). 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.[1] Instead, BeH is prepared from preformed beryllium(II) compounds. It was first synthesized in 1951 by treating dimethylberyllium, Be(CH), with lithium aluminium hydride, LiAlH.[2]
Purer BeH forms from the pyrolysis of di-tert-butylberyllium, Be(C[CH{{sub|3}}]) at 210°C.[3]
A route to highly pure samples involves the reaction of triphenylphosphine, PPh, with beryllium borohydride, Be(BH):
Be(BH) + 2 PPh → BeH + 2 PhPBH
Isolated molecules of (sometimes called dihydridoberyllium and written to emphasize the differences with the solid state) are only stable as a dilute gas. When condensed, unsolvated will spontaneously autopolymerise.
Free molecular BeH 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.[4]
BeH is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm) was reported,[5] prepared by heating amorphous BeH 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 BeH tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH.[6]
Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.[7]
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as hydrogen chloride to form beryllium chloride.[1]
BeH + 2 HO → Be(OH) + 2 H
BeH + 2 HCl → BeCl + 2 H
The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction:[8]
+ L → 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 LiBeH and LiBeH. The latter contains the tetrahydridoberyllate(2-) anion .
Beryllium hydride reacts with trimethylamine, N(CH) to form a dimeric adduct with bridging hydrides.[9] However, with dimethylamine, HN(CH) it forms a trimeric beryllium diamide, [Be(N(CH{{sub|3}}){{sub|2}}){{sub|2}}], and hydrogen.