Strontium fluoride

Strontium fluoride
Other names

Strontium difluoride
Strontium(II) fluoride
Identifiers
CAS number 7783-48-4 Y
ChemSpider 74190 Y
Jmol-3D images Image 1
Properties
Molecular formula SrF2
Molar mass 125.62 g/mol
Density 4.24 g/cm3
Melting point

1477 °C
Boiling point

2460 °C
Solubility in water 0.039 g/100 g
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
EU Index Not listed
Flash point Non-flammable
Related compounds
Other anions Strontium chloride
Strontium bromide
Strontium iodide
Other cations beryllium fluoride
magnesium fluoride
calcium fluoride
barium fluoride
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

Contents

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 polarisation 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 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.[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.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
  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:
  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. ^ http://www.newmet.co.uk/Products/koch/strontium.php
  5. ^ http://www.crystran.co.uk/strontium-fluoride-srf2.htm