Scandium fluoride

Scandium fluoride
Names
	IUPAC name Scandium(III) fluoride
	Other names Scandium trifluoride
Identifiers
CAS Number	13709-47-2 ;
3D model (JSmol)	Interactive image;
ECHA InfoCard	100.033.854
EC Number	237-555-4;
PubChem CID	83678;
RTECS number	VQ8930000;
CompTox Dashboard (EPA)	DTXSID7065594 ;
	InChI InChI=1S/3FH.Sc/h3*1H;/q;;;+3/p-3;
	SMILES F[Sc](F)F;
Properties
Chemical formula	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]
Solubility product (Ksp)	5.81×10−24[2]
Structure
Crystal structure	Cubic, Pm3m
Space group	Pm3m, No. 221
Hazards
NFPA 704 (fire diamond)	2 0 0
Related compounds
Other anions	Scandium(III) chloride; Scandium(III) bromide; Scandium(III) iodide
Other cations	Yttrium(III) fluoride; Lutetium(III) fluoride
Related compounds	Scandium(III) nitrate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Scandium(III) fluoride, ScF₃, is an ionic compound. This salt 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.[3] It is also formed during the extraction from the ore thortveitite by the reaction of Sc₂O₃ with ammonium bifluoride at high temperature:[4]

Sc₂O₃ + 6 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.[4] Further purification steps are required to produce usable metallic scandium.[4]

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.[5] 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).[6]

At ambient pressures scandium trifluoride adopts the cubic crystal system, using the perovskite structure with one metal position vacant.[7] The unit cell dimension is 4.01 Å.[7] Under pressure scandium trifluoride also forms different crystal structures with rhombohedral, and above 3 GPa tetrahedral.[7]

References

Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier, ISBN 0-12-352651-5.
John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
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.
Pradyot Patnaik, 2003, Handbook of Inorganic Chemicals, McGraw-Hill Professional, ISBN 0-07-049439-8.
Woo, Marcus (7 November 2011). "An incredible shrinking material: Engineers reveal how scandium trifluoride contracts with heat". Physorg. Retrieved 8 November 2011.
Greve, Benjamin K.; Kenneth L. Martin; Peter L. Lee; Peter J. Chupas; Karena W. Chapman; Angus P. Wilkinson (19 October 2010). "Pronounced Negative Thermal Expansion from a Simple Structure: Cubic ScF₃". Journal of the American Chemical Society. 132 (44): 15496–15498. doi:10.1021/ja106711v. PMID 20958035.
Aleksandrov, K. S.; V. N. Voronov; A. N. Vtyurin; A. S. Krylov; M. S. Molokeev; M. S. Pavlovskiĭ; S. V. Goryaĭnov; A. Yu. Likhacheva; A. I. Ancharov (2009). "Pressure-induced phase transition in the cubic ScF3 crystal". Physics of the Solid State. 51 (4): 810–816. Bibcode:2009PhSS...51..810A. doi:10.1134/S1063783409040295. ISSN 1063-7834. S2CID 119874020.

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[Wiberg&Holleman-1] Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier, ISBN 0-12-352651-5.

[crc-2] John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.

[Simon_Cotton-3] 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.

[Patnaik-4] Pradyot Patnaik, 2003, Handbook of Inorganic Chemicals, McGraw-Hill Professional, ISBN 0-07-049439-8.

[woo-5] Woo, Marcus (7 November 2011). "An incredible shrinking material: Engineers reveal how scandium trifluoride contracts with heat". Physorg. Retrieved 8 November 2011.

[greve-6] Greve, Benjamin K.; Kenneth L. Martin; Peter L. Lee; Peter J. Chupas; Karena W. Chapman; Angus P. Wilkinson (19 October 2010). "Pronounced Negative Thermal Expansion from a Simple Structure: Cubic ScF₃". Journal of the American Chemical Society. 132 (44): 15496–15498. doi:10.1021/ja106711v. PMID 20958035.

[Aleksandrov2009-7] Aleksandrov, K. S.; V. N. Voronov; A. N. Vtyurin; A. S. Krylov; M. S. Molokeev; M. S. Pavlovskiĭ; S. V. Goryaĭnov; A. Yu. Likhacheva; A. I. Ancharov (2009). "Pressure-induced phase transition in the cubic ScF3 crystal". Physics of the Solid State. 51 (4): 810–816. Bibcode:2009PhSS...51..810A. doi:10.1134/S1063783409040295. ISSN 1063-7834. S2CID 119874020.