Scandium fluoride

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Scandium fluoride
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Names
IUPAC name
Scandium(III) fluoride
Other names
Scandium trifluoride
Identifiers
13709-47-2 N
EC Number 237-555-4
Jmol 3D model Interactive image
PubChem 83678
RTECS number VQ8930000
  • InChI=1S/3FH.Sc/h3*1H;/q;;;+3/p-3
  • F[Sc](F)F
Properties
ScF3
Molar mass 101.95112 g/mol
Appearance bright white powder
Density 2.53 g/cm3
Melting point 1,552 °C (2,826 °F; 1,825 K)[1]
Boiling point 1,607 °C (2,925 °F; 1,880 K)[1]
Structure
Cubic, Pm3m
Pm3m, No. 221
Vapor pressure {{{value}}}
Related compounds
Related compounds
 Scandium(III) chloride
Scandium(III) nitrate
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

Scandium(III) fluoride, ScF3, is an ionic compound. It is slightly soluble in water but dissolves in the presence of excess fluoride to form the ScF63− anion.[1]

Production

ScF3 can be produced by reacting scandium and fluorine.[2] It is also formed during the extraction from the ore thortveitite by the reaction of Sc2O3 with ammonium bifluoride at high temperature:[3]

Sc2O3 + NH4HF2 → 2 ScF3 + 6 NH4F + 3 H2O

The resulting mixture contains a number of metal fluorides and this is reduced by reaction with calcium metal at high temperature.[3] Further purification steps are required to produce usable metallic scandium.[3]

Properties

Scandium trifluoride exhibits the unusual property of negative thermal expansion, meaning it shrinks when heated. This phenomenon is explained by the quartic oscillation of the fluoride ions. The energy stored in the bending strain of the fluoride ion is proportional to the fourth power of the displacement angle, unlike most other materials where it is proportional to the square of the displacement. A fluorine atom is bound to two scandium atoms, and as temperature increases the fluorine oscillates more perpendicularly to its bonds. This motion draws the scandium atoms together throughout the bulk material, which contracts.[4] ScF3 exhibits this property from at least 10 K to 1100 K above which it shows the normal positive thermal expansion; furthermore, the material has cubic symmetry over this entire temperature range, and up to at least 1600 K at ambient pressure. The negative thermal expansion at very low temperatures is quite strong (coefficient of thermal expansion around -14 ppm/K between 60 and 110 K).[5]

At ambient pressures scandium trifluoride adopts the cubic crystal system, using the perovskite structure with one metal position vacant.[6] The unit cell dimension is 4.01 Å.[6] Under pressure scandium trifluoride also forms different crystal structures with rhombohedral, and above 3 GPa tetrahedral.[6]

References

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  1. ↑ 1.0 1.1 1.2 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier, ISBN 0-12-352651-5.
  2. ↑ S.A.Cotton, Scandium, Yttrium and the Lanthanides: Inorganic and Coordination Chemistry, Encyclopedia of Inorganic Chemistry, 1994, John Wiley & Sons, ISBN 0-471-93620-0.
  3. ↑ 3.0 3.1 3.2 Pradyot Patnaik, 2003, Handbook of Inorganic Chemicals, McGraw-Hill Professional, ISBN 0-07-049439-8.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 6.2 Lua error in package.lua at line 80: module 'strict' not found.
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