Structure and Bonding
The structure of solid BeF2 resembles that of silicon dioxide. Be2+ centers are four coordinate and tetrahedral. 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. 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. 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.
BeF2 reaches a vapor pressure of 10 Pa at 686 °C, 100 Pa at 767 °C, 1 kilopascal at 869 °C, 10 kPa at 999 °C, and 100 kPa at 1172 °C.
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
Read more about this topic: Beryllium Fluoride
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