Beryllium fluoride

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

File:Beryllium-fluoride-3D-vdW.png

The structure of solid BeF₂ resembles that of cristobalite. Be²⁺ centers are four coordinate and tetrahedral and the fluoride centers are two-coordinate.Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications {{ISBN|0-19-855370-6}} The Be-F bond lengths are about 1.54 Å.Pallavi Ghalsasi, Prasanna S. Ghalsasi, "Single Crystal X-Ray Structure of BeF2: α-Quartz" Inorg. Chem., 2011, 50 (1), pp 86–89. {{doi|10.1021/ic101248g}} 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 beryllium fluoride adopts a linear structure, with a Be-F distance of 143 pm. BeF₂ reaches a vapor pressure 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.Vapor pressure, physics.nyu.edu, [http://www.physics.nyu.edu/kentlab/How_to/ChemicalInfo/VaporPressure/morepressure.pdf p. 6-63], from Ohe, S. (1976) Computer Aided Data Book of Vapor Pressure, Data Book Publishing Co., Tokyo. Molecular {{chem2|BeF2}} in the gaseous state is isoelectronic to carbon dioxide.

As a liquid, beryllium fluoride has a tetrahedral 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 units.{{cite journal

| title = Waterlike Structural and Excess Entropy Anomalies in Liquid Beryllium Fluoride

|author1=Agarwal, M. |author2=Chakravarty C | journal = J. Phys. Chem. B

| year = 2007

| volume = 111

| pages = 13294–300

| doi = 10.1021/jp0753272

| pmid = 17963376

| issue = 46

}}

The processing of beryllium ores generates impure Be(OH)₂. This material reacts with ammonium bifluoride 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.{{Greenwood&Earnshaw}}

Reduction of BeF₂ at 1300 °C with magnesium in a graphite crucible provides the most practical route to metallic beryllium:Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.

:BeF₂ + Mg → Be + MgF₂

Beryllium chloride is not a useful precursor because of its volatility. {{citation needed|reason = The page on Beryllium specifically states that electrolysis of BeCl2 is a practical industrial path to metallic beryllium.|date=November 2018}}

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.{{cite journal

| title = The structure of bovine F1-ATPase inhibited by ADP and beryllium fluoride

| author = Reiko Kagawa

| author2 = Martin G. Montgomery

| author3 = Kerstin Braig

| author4 = Andrew G. W. Leslie

| author5 = John E. Walker

| journal =The EMBO Journal

| year = 2004

| volume = 23

| issue = 5

| pages = 2734–2744

| doi = 10.1038/sj.emboj.7600293

| pmid = 15229653

| pmc = 514953

}}{{cite journal | title=Fluoride complexes of aluminium or beryllium act on G-proteins as reversibly bound analogues of the gamma phosphate of GTP |author=Bigay J. |author2=Deterre P. |author3=Pfister C. |author4=Chabre M. | journal = The EMBO Journal | year=1987 | volume=6 | issue=10 | pages=2907–2913 |doi=10.1002/j.1460-2075.1987.tb02594.x | pmid=2826123 | pmc=553725}}

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 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.

{{see|Beryllium poisoning}}

Beryllium compounds are highly toxic. The increased toxicity of beryllium in the presence of fluoride has been noted as early as 1949.{{Cite book |url=https://www.nap.edu/read/11571 |title=Fluoride in Drinking Water: A Scientific Review of EPA's Standards |publisher=The National Academies Press |year=2006 |isbn=978-0-309-10128-8 |pages=51–52 |language=en |doi=10.17226/11571}} The {{LD50}} in mice is about 100 mg/kg by ingestion and 1.8 mg/kg by intravenous injection.

{{Reflist}}

• [https://web.archive.org/web/20051015082353/http://www-cie.iarc.fr/htdocs/monographs/vol58/mono58-1.htm IARC Monograph "Beryllium and Beryllium Compounds"]
• [https://web.archive.org/web/20051214061938/http://www.npi.gov.au/database/substance-info/profiles/13.html National Pollutant Inventory: Beryllium and compounds fact sheet]
• [https://web.archive.org/web/20060116134617/http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory: Fluoride and compounds fact sheet]
• [http://inchem.org/documents/icsc/icsc/eics1355.htm Hazards of Beryllium fluoride]
• [https://web.archive.org/web/20070924182058/http://www.camd.lsu.edu/msds/b/beryllium_fluoride.htm MSDS from which the LD50 figures]

{{Beryllium compounds}}

{{Fluorides}}

{{DEFAULTSORT:Beryllium Fluoride}}

Category:Beryllium compounds

Category:Fluorides

Category:Alkaline earth metal halides

Category:Highly-toxic chemical substances