Ammonium tetrafluoroberyllate

Diammonium tetrafluoroberyllate is one of several salts of the tetrafluoroberyllate anion, in which four fluorine atoms are covalently bonded to a beryllium atom in a tetrahedral arrangement. The anion has also been prepared as salts of alkali metals, alkaline earths, transition metals, and many organic amines, some with varying degrees of hydration.

Also called ammonium beryllium fluoride, the salt is formed by dissolving beryllium hydroxide [Be(OH)₂] in an aqueous solution of ammonium hydrogen fluoride [(NH₄)HF₂]. The aqueous solution is concentrated in an evaporative crystallizer to form the diammonium tetrafluoroberyllate salt. Its crystals are orthorhombic (shown) with a density of 1.71 g/mL. Like all beryllium-containing compounds, it is extremely toxic.

Diammonium tetrafluoroberyllate is used to produce beryllium fluoride (BeF₂) glass by heating the salt to ≈1000 °C. BeF₂, in turn, can be used to make beryllium metal by reducing it with elemental magnesium at 1300 °C. In the past several years, beryllium has been in short supply; in 2016, L. N. Malyutin and co-workers at Tomsk Polytechnic University (Russia) developed improved methods to purify diammonium tetrafluoroberyllate on its way to making the metal.

Advanced materials manufacturers, such as Materion (Mayfield Heights, OH), use ammonium tetrafluoroberyllate to make their beryllium-containing products. Materion uses the synthetic route described above to make BeF₂ and the metal.

In addition to being the precursor to the metal, BeF₂ has applications in the nuclear energy industry. Beryllium metal produced from ammonium tetrafluoroberyllate was used to make the mirrors of the James Webb Space Telescope, which is  scheduled to be launched later this year.