Beryllium fluoride: Difference between revisions
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Revision as of 07:22, 1 June 2010
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| Names | |
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| IUPAC name
Berylium fluoride
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.029.198 |
PubChem CID
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| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |
| BeF2 | |
| Molar mass | 47.01 g/mol hygroscopic |
| Appearance | colorless lumps |
| Density | 1.986 g/cm3 |
| Melting point | 554 °C (1,029 °F; 827 K) |
| Boiling point | 1,169 °C (2,136 °F; 1,442 K) |
| very soluble | |
| Solubility | sparingly soluble in alcohol |
| Structure | |
| Linear | |
| Thermochemistry | |
Heat capacity (C)
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1.102 J/K |
Std enthalpy of
formation (ΔfH⦵298) |
-21.84 kJ/g |
| Hazards | |
| Flash point | non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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98 mg/kg (oral, rat) |
| Related compounds | |
Other anions
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Beryllium chloride Beryllium bromide Beryllium iodide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Beryllium fluoride is the inorganic compound with the formula BeF2. This white solid is the principal precursor for the manufacture of beryllium metal.
Structure
Solid BeF2 has a silica-like structure with four coordinate, tetrahedral beryllium.[2] It is the binary beryllium compound with the greatest ionic character due to the great difference between the electronegativity of F and Be. Even so, it is considered highly covalent. Solid BeF2 adopts a number of polymeric structures analogous to those adopted by SiO2 namely α-quartz, β-quartz, crystobalite and tridymite,[3]. An analogy exists between BeF2 and AlF3: both adopt extended structures at mild temperature.
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]
Production
The processing of beryllium ores generates an impure Be(OH)2. This material reacts with ammonium bifluoride to give ammonium tetrafluorberyllate:
- Be(OH)2 + 2 (NH4)HF2 → (NH4)2BeF4 + 2 H2O
Tetrafluorberyllate 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
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.
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]
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, into which fluorides of uranium and thorium are introduced. Beryllium fluoride is exceptionally chemically stable and LiF/BeF2 mixtures have low melting points and the best neutronic properties of fluoride salt combinations appropriate for reactor use.
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.
References
- ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
- ^ 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.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- ^ 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: 13294. doi:10.1021/jp0753272.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link)