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. 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.
Purer BeH forms from the pyrolysis of di-tert-butylberyllium, Be(C[CH]) at 210ðC.
A route to highly pure samples involves the reaction of triphenylphosphine, PPh, with beryllium borohydride, Be(BH):
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.
BeH most often is formed as an amorphous white powder by decomposing various organo-beryllium compounds, which has been shown to consist of a network of corner sharing tetrahedra.
Early work showed that there are multiple phases of BeH, with the low temperature, higher-density phase shown to have a hexagonal crystalline form by selected-area electron diffraction (SAED), but this structure has not been solved to date. The other phase was argued to have either a monoclinic or tetragonal cell.
Further synchrotron Powder X-ray diffraction studies of the higher-density phase of BeH have shown crystalline beryllium hydride to have a body-centered orthorhombic unit cell (space group Ibam), containing a network of corner-sharing BeH tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH. The Be-H bond length is significantly shorter in for the orthorhomibic crystal shown than would be assumed in the hydrogen-bridged infinite chain model, with greater bond angles found in the BeH2 crystal structure compared to the 90ð angles expected in the hydrogen-bridged model. Before the structure was solved by synchrotron X-ray diffraction, it was thought that there was hydrogen-bridging.
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as hydrogen chloride to form beryllium chloride.
The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction:
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. However, with dimethylamine, HN(CH) it forms a trimeric beryllium diamide, [Be(N(CH))], and hydrogen.