Strontium fluoride

Strontium fluoride, SrF2, also called strontium difluoride and strontium(II) fluoride, is a fluoride of strontium. It is a brittle white crystalline solid. In nature, it appears as the very rare mineral strontiofluorite.[2][3]

Strontium fluoride
strontium fluoride
Names
Other names
Strontium difluoride
Strontium(II) fluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.091
EC Number
  • 232-00-3
UNII
  • InChI=1S/2FH.Sr/h2*1H;/q;;+2/p-2 checkY
    Key: FVRNDBHWWSPNOM-UHFFFAOYSA-L checkY
  • InChI=1/2FH.Sr/h2*1H;/q;;+2/p-2
    Key: FVRNDBHWWSPNOM-NUQVWONBAO
  • [Sr+2].[F-].[F-]
Properties
SrF2
Molar mass 125.62 g/mol
Density 4.24 g/cm3
Melting point 1,473 °C (2,683 °F; 1,746 K)
Boiling point 2,460 °C (4,460 °F; 2,730 K)
0.117 g/100 mL
4.33×10−9[1]
−37.2·10−6 cm3/mol
1.439 @0.58 µm
Structure
cubic crystal system, cF12
Fm3m, #225
a = 5.80 Å, b = 5.80 Å, c = 5.80 Å
α = 90°, β = 90°, γ = 90°
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

Preparation

Strontium fluoride is prepared by the action of hydrofluoric acid on strontium carbonate.[4]

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°.[5] 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.[6] 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.[7]

Properties

It is almost insoluble in water (its Ksp 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.[8]

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.[9]

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. John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
  2. "Strontiofluorite".
  3. "List of Minerals". 21 March 2011.
  4. W. Kwasnik (1963). "Strontium Fluoride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY, NY: Academic Press. p. 234.
  5. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  6. 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
  7. 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
  8. "Newmet Koch - Strontium". Archived from the original on 2005-12-14.
  9. Mediatopia Ltd. "Strontium Fluoride (SrF2) Optical Material". Crystran.co.uk. Retrieved 2012-08-18.
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