Beryllium fluoride
| Beryllium fluoride | |
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Berylium fluoride |
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| Identifiers | |
| CAS number | 7787-49-7  |
| PubChem | 24589 |
| ChemSpider | 22992 |
| ChEBI | CHEBI:49499 |
| RTECS number | DS2800000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | BeF2 |
| Molar mass | 47.01 g/mol hygroscopic |
| Appearance | colorless lumps |
| Density | 1.986 g/cm3 |
| Melting point |
554 °C, 827 K, 1029 °F |
| Boiling point |
1169 °C, 1442 K, 2136 °F ([1]) |
| Solubility in water | very soluble |
| Solubility | sparingly soluble in alcohol |
| Structure | |
| Molecular shape | Linear |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
-21.84 kJ/g |
| Specific heat capacity, C | 1.102 J/K |
| Hazards | |
| EU Index | 004-002-00-2 |
| EU classification | Carc. Cat. 2 Highly toxic (T+) Irritant (Xi) Dangerous for the environment (N) |
| R-phrases | R49, R25, R26, R36/37/38, R43, R48/23, R51/53 |
| S-phrases | S53, S45, S61 |
| Flash point | non-flammable |
| LD50 | 98 mg/kg (oral, rat) |
| Related compounds | |
| Other anions | Beryllium chloride Beryllium bromide Beryllium iodide |
| Other cations | magnesium fluoride calcium fluoride strontium fluoride barium fluoride |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Beryllium fluoride is the inorganic compound with the formula BeF2. This white solid is the principal precursor for the manufacture of beryllium metal.
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[edit] Structure and bonding
The structure of solid BeF2 resembles that for silicon dioxide. Be2+ centers are four coordinate and tetrahedral.[2] Solid BeF2 adopts a number of polymeric structures analogous to those adopted by SiO2 namely α-quartz, β-quartz, crystobalite and tridymite, and its reactions with fluorides are quite analogous to the reactions of SiO2 with oxides.[3] An analogy exists between BeF2 and AlF3: both adopt extended structures at mild temperature. BeF2 is considered to be highly covalent.
Gaseous BeF2 is found in the gas-phase above 1160 °C. Like the isoelectronic gases CO2 and SiO2, it is a linear molecule. The Be-F distance of 177 pm.[4] The difference between the ambient temperature structures of BeF2 (rock-like solid) and CO2 (gas) reflects the low tendency of alkali metals to form multiple bonds.
Molten BeF2 resembles water in some ways, since it is a triatomic molecule with strong interactions via Be—F—Be bonds. As in water, the density of BeF2 decreases near its melting point. Liquid (molten) beryllium fluoride also has a fluctuating tetrahedral structure[5]
[edit] Production
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
[edit] Applications
Reduction of BeF2 at 1300 °C with magnesium in a graphite crucible provides the most practical route to metallic beryllium:[4]
- BeF2 + Mg → Be + MgF2
The chloride is not a useful precursor because of its volatility.
[edit] 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.[6][7]
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 C - 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.
[edit] Safety
All beryllium compounds are highly toxic. Beryllium fluoride is very soluble in water and is thus absorbed easily; as mentioned above, it inhibits ATP uptake. The LD50 in mice is about 100 mg/kg by ingestion and 1.8 mg/kg by intravenous injection.
[edit] References
- ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
- ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.
- ^ a b Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ^ Agarwal, M.; Chakravarty C (2007). "Waterlike Structural and Excess Entropy Anomalies in Liquid Beryllium Fluoride". J. Phys. Chem. B 111 (46): 13294. doi:10.1021/jp0753272. PMID 17963376.
- ^ Reiko Kagawa, Martin G Montgomery, Kerstin Braig, Andrew G W Leslie and John E Walker (2004). "The structure of bovine F1-ATPase inhibited by ADP and beryllium fluoride". The EMBO Journal 23 (5): 2734–2744. doi:10.1038/sj.emboj.7600293. PMC 514953. PMID 15229653. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=514953.
- ^ Bigay J, Deterre P, Pfister C, Chabre M (1987). "Fluoride complexes of aluminium or beryllium act on G-proteins as reversibly bound analogues of the gamma phosphate of GTP.". The EMBO Journal 6 (10): 2907–2913. PMC 553725. PMID 2826123. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=553725.
[edit] External links
- IARC Monograph "Beryllium and Beryllium Compounds"
- National Pollutant Inventory: Beryllium and compounds fact sheet
- National Pollutant Inventory: Fluoride and compounds fact sheet
- Hazards of Beryllium fluoride
- MSDS from which the LD50 figures
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