Description
Barium arsenide has the molecular formula of Ba3As2.
By passing arsine over barium oxide, at red heat,
a mixture of arsenide and arsenite is obtained. The
best way is to react the elements together at red heat:
3Ba + 2Ar Ba3As2
Since Ba metal melts at 729 °C, the metal is melted at
750 °C and vapors of As are passed over it in a stream of
argon gas. Crystals of Ba3As2 slowly form in cooler parts
of the enclosed tube furnace. It can also be prepared in a pure form by reduction of bariumarsenate with carbon
in an electric furnace:
2Ba3AsO4 + 3C + heat Ba3As2 + 3BaO + 2CO2 + CO
The oxide produced may be removed by washing in
an acid like HCl to solubilize it. The crystals obtained
are deep brown with a density of 4.16 g/cm
3. Its molecular
weight is 561.9324 g/mol.
Physical properties
Barium arsenide is very similar in chemical properties
to the arsenides of calcium and strontium. It is slightly darker in color, more
readily fusible and more reactive chemically. It burns
spontaneously in fluorine, chlorine or bromine vapor. In
oxygen, it burns at about 300°C to form the orthoarsenate
and in sulfur vapor at dull red heat to form thioarsenates.
Ba3As2 has the body-centered cubic structure with
a = 9.846, where 1/9 of the anion sites are empty.
Barium arsenide also forms double salts such as
Li4Ba3As4 (Orthorhombic space group = Immm) which
is isostructural with Li4Sr3Sb4 and Li4Ba3Sb4. It contains
two anionic moieties, namely As2
4- dumbbells and As
3-,
and consists of planes of BaAs6 octahedra separated by
corrugated sheets of Li and Ba atoms.
