Beryllium hydride

BeschreibungBeH2 was first synthesized in 1951 by reacting dimethylberyllium, Be(CH3)2, with lithium aluminum hydride, LiAlH4. A purer grade of BeH2 can also be formed from the pyrolysis of di-tert-butylberyllium, {Be(C(CH3)3)2} at 210°C. The purest beryllium hydride is obtained by the reaction of triphenylphosphine, i.e. PPh3,with berylliumborohydride,Be(BH4)2 by the reaction: Be(BH4)2+2PPh3→2Ph3PBH3 + BeH2 Note that unlike the other elements in Group IIA where the hydride can be prepared by reaction of the elements, the reaction of the metal with hydrogen to produce beryllium hydride has not proved possible. BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm3) has also been reported. This was 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 bodycentered orthorhombic unit cell, containing a network of corner-sharing BeH4 tetrahedra (there are 12BeH2 molecules in the unit cell) 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 cornershared tetrahedra. The density is 0.755 g/cm3.

VerwendenBeryllium hydride (BeH2) liberates hydrogen gas when mixed with water. It is used as a source of hydrogen in experimental rockets and fuel cells. It has also been considered as a moderator for nuclear reactors. Methods of preparing and densifying the pure compound are described in a large number of patents. However, the toxicity has always been a serious barrier to its commercial exploitation.