|Jmol-3D images||Image 1|
|Molar mass||47.01 g/mol
|Melting point||554 °C (1,029 °F; 827 K)|
|Boiling point||1,169 °C (2,136 °F; 1,442 K)|
|Solubility in water||very soluble|
|Solubility||sparingly soluble in alcohol|
|Crystal structure||Trigonal, α-quartz|
|Space group||P3121 (No. 152), Pearson symbol hP9|
|Lattice constant||a = 473.29 pm, c = 517.88 pm|
|1.102 J/K or 59 J/mol K|
|45 J/mol K|
Std enthalpy of
|-1028.2 kJ/g or -1010 kJ/mol|
Gibbs free energy (ΔG)
|EU classification||Carc. Cat. 2
Highly toxic (T+)
Dangerous for the environment (N)
|R-phrases||R49, R25, R26, R36/37/38, R43, R48/23, R51/53|
|S-phrases||S53, S45, S61|
|LD50||98 mg/kg (oral, rat)|
|Other anions||Beryllium chloride
|Other cations||Magnesium fluoride
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Beryllium fluoride is the inorganic compound with the formula BeF2. This white solid is the principal precursor for the manufacture of beryllium metal. Its structure resembles that of quartz, but BeF2 is highly soluble in water.
Beryllium fluoride has unique optical properties. In the form of fluoroberyllate glass it has the lowest refractive index for a solid at room temperature of 1.275. It dispersive power is the lowest for a solid at 0.0093, and the non linear coefficient is also the lowest at 2 × 10−14.
Structure and bonding
The structure of solid BeF2 resembles that of cristobalite. 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
Molten BeF2 resembles water in some ways. Both liquid consist of triatomic molecules with strong intermolecular interactions. As in water, the density of BeF2 decreases near its melting point. Liquid (molten) beryllium fluoride also has a fluctuating tetrahedral structure.
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.
- 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.
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.
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.
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- 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