Chemical Properties
white, amorphous solid; inert to laboratory air; can be prepared by continuous thermal decomposition of a di-t-butylberyllium ethyl ether complex in a boiling hydrocarbon; has found use as rocket fuel and as a moderator for nuclear reactors [KIR80] [MER06]
Description
BeH2 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.
Physical properties
White amorphous solid; density 0.65 g/cm3; decomposes at 250°C; reacts with water.
Uses
Beryllium hydride (BeH2) liberates hydrogen gas when mixed with water. It is used as a
source of hydrogen in experimental rockets and fuel cells.
Definition
ChEBI: Beryllium dihydride is a beryllium hydride.
Preparation
Beryllium hydride is made by treating an ethereal solution of beryllium borohydride with triphenylphosphine, or by pyrolysis of di-tert-butylberyllium.
Safety Profile
Confirmed carcinogen. Adangerous fire hazard. When heated to 220°C it liberatesexplosive hydrogen gas. Reacts violently with methanol,water, and dilute acids. When heated to decomposition itemits toxic fumes of BeO. See BERYLLIUMCOMPOUNDS and HYDRIDE
