Beryllium fluoride is the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Be F₂. This white solid is the principal precursor for the manufacture of

beryllium Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...

metal. Its structure resembles that of quartz, but BeF₂ is highly soluble in water.

Properties

Beryllium fluoride has distinctive optical properties. In the form of fluoroberyllate glass, it has the lowest

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

for a solid at room temperature of 1.275. Its dispersive power is the lowest for a solid at 0.0093, and the nonlinear coefficient is also the lowest at 2 × 10⁻¹⁴.

Structure and bonding

The structure of solid BeF₂ resembles that of

cristobalite Cristobalite ( ) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, Si O2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members o ...

. Be²⁺ centers are four coordinate and tetrahedral and the fluoride centers are two-coordinate. The Be-F bond lengths are about 1.54 Å. Analogous to SiO₂, BeF₂ can also adopt a number of related structures. An analogy also exists between BeF₂ and AlF₃: both adopt extended structures at mild temperature.

Gaseous and liquid BeF₂

Gaseous beryllium fluoride adopts a linear structure, with a Be-F distance of 143 pm. BeF₂ reaches a

vapor pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

of 10 Pa at 686 °C, 100 Pa at 767 °C, 1 kPa at 869 °C, 10 kPa at 999 °C, and 100 kPa at 1172 °C. Molecular in the gaseous state is isoelectronic to

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. As a liquid, beryllium fluoride has a

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

structure. The density of liquid BeF₂ decreases near its freezing point, as Be²⁺ and F⁻ ions begin to coordinate more strongly with one another, leading to the expansion of voids between

formula unit In chemistry, a formula unit is the smallest unit of a non-molecular substance, such as an ionic compound, covalent network solid, or metal. It can also refer to the chemical formula for that unit. Those structures do not consist of discrete mol ...

Production

The processing of beryllium ores generates impure Be(OH)₂. This material reacts with

ammonium bifluoride Ammonium bifluoride is an inorganic compound with the formula or . It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-industrial etching, etchant and an intermediate in a once-contemplated route to hydrofluoric acid ...

to give ammonium tetrafluoroberyllate: :Be(OH)₂ + 2 (NH₄)HF₂ → (NH₄)₂BeF₄ + 2 H₂O Tetrafluoroberyllate is a robust ion, which allows its purification by precipitation of various impurities as their hydroxides. Heating purified (NH₄)₂BeF₄ gives the desired product: :(NH₄)₂BeF₄ → 2 NH₃ + 2 HF + BeF₂ In general the reactivity of BeF₂ ions with fluoride are quite analogous to the reactions of SiO₂ with oxides.

Applications

Reduction of BeF₂ at 1300 °C with magnesium in a

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

crucible A crucible is a container in which metals or other substances may be melted or subjected to very high temperatures. Although crucibles have historically tended to be made out of clay, they can be made from any material that withstands temperat ...

provides the most practical route to metallic beryllium:Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. . :BeF₂ + Mg → Be + MgF₂

Beryllium chloride Beryllium chloride is an inorganic compound with the formula BeCl2. It is a colourless, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to beryllium's diagonal relations ...

is not a useful precursor because of its volatility.

Niche uses

Beryllium fluoride is used in biochemistry, particularly protein crystallography as a mimic of phosphate. Thus, ADP and beryllium fluoride together tend to bind to ATP sites and inhibit protein action, making it possible to crystallise proteins in the bound state. Beryllium fluoride forms a basic constituent of the preferred fluoride salt mixture used in liquid-fluoride nuclear reactors. Typically beryllium fluoride is mixed with

lithium fluoride Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid that transitions to white with decreasing crystal size. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. ...

to form a base solvent ( FLiBe), into which fluorides of uranium and thorium are introduced. Beryllium fluoride is exceptionally chemically stable, and LiF/BeF₂ mixtures ( FLiBe) have low melting points (360–459 °C) and the best neutronic properties of fluoride salt combinations appropriate for reactor use. MSRE used two different mixtures in the two cooling circuits.

Safety

Beryllium compounds are highly toxic. The increased toxicity of beryllium in the presence of fluoride has been noted as early as 1949. The in mice is about 100 mg/kg by ingestion and 1.8 mg/kg by intravenous injection.

References

External links

IARC Monograph "Beryllium and Beryllium Compounds"

* ttps://web.archive.org/web/20060116134617/http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory: Fluoride and compounds fact sheet
Hazards of Beryllium fluoride

{{DEFAULTSORT:Beryllium Fluoride Beryllium compounds Fluorides Alkaline earth metal halides Highly-toxic chemical substances