Strontium fluoride

Strontium fluoride

Names
Other names Strontium difluoride Strontium(II) fluoride
Identifiers
CAS Number	7783-48-4
ChemSpider	74190
EC Number	232-00-3
Jmol interactive 3D	Image
PubChem	82210
InChI InChI=1S/2FH.Sr/h2*1H;/q;;+2/p-2 Key: FVRNDBHWWSPNOM-UHFFFAOYSA-L InChI=1/2FH.Sr/h2*1H;/q;;+2/p-2 Key: FVRNDBHWWSPNOM-NUQVWONBAO
SMILES [Sr+2].[F-].[F-]
Properties
Chemical formula	SrF2
Molar mass	125.62 g/mol
Density	4.24 g/cm^3
Melting point	1,477 °C (2,691 °F; 1,750 K)
Boiling point	2,460 °C (4,460 °F; 2,730 K)
Solubility in water	0.039 g/100 mL
Refractive index (nD)	1.439 @0.58 µm
Structure
Crystal structure	cubic crystal system, cF12
Space group	Fm3m, #225
Coordination geometry	Sr, 8, cubic F, 4, tetrahedral
Hazards
Flash point	Non-flammable
Related compounds
Other anions	Strontium chloride Strontium bromide Strontium iodide
Other cations	beryllium fluoride magnesium fluoride calcium fluoride barium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Strontium fluoride, SrF₂, also called strontium difluoride and strontium(II) fluoride, is a fluoride of strontium. It is a stable brittle white crystalline solid with melting point of 1477 °C and boiling point 2460 °C.

Preparation

Strontium fluoride is prepared by reaction of strontium chloride with fluorine gas, or by action of hydrofluoric acid on strontium carbonate.

Structure

The solid adopts the fluorite structure. In the vapour phase the SrF₂ molecule is non-linear with an F-Sr-F angle of approximately 120°.^[1] This is an exception to VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible.^[2] Another proposal is that polarization of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with the Sr-F bonds.^[3]

Properties

It is almost insoluble in water (its K_sp value is approximately 2.0x10⁻¹⁰ at 25 degrees Celsius.
It irritates eyes and skin, and is harmful when inhaled or ingested.
Similar to CaF₂ and BaF₂, SrF₂ displays superionic conductivity at elevated temperatures.^[4]
Strontium fluoride is transparent to light in the wavelengths from vacuum ultraviolet (150 nm) to infrared (11 µm). Its optical properties are intermediate to calcium fluoride and barium fluoride.^[5]

Uses

Strontium fluoride is used as an optical material for a small range of special applications, for example, as an optical coating on lenses and also as a thermoluminescent dosimeter crystal. Another use is as a carrier of strontium-90 radioisotope in radioisotope thermoelectric generators.

References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
2. Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX₂ (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)Seijo L.,Barandiarán Z J. Chem. Phys. 94, 3762 (1991) doi:10.1063/1.459748
3. Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba Bytheway I, Gillespie RJ, Tang TH, Bader RF Inorganic Chemistry, Vol.34, No.9, 2407-2414, 1995 doi:10.1021/ic00113a023
4. https://web.archive.org/20051214052733/http://www.newmet.co.uk:80/Products/koch/strontium.php
5. Mediatopia Ltd. "http://www.crystran.co.uk/strontium-fluoride-srf2.htm". Crystran.co.uk. Retrieved 2012-08-18. External link in |title= (help)