Iron(III) fluoride

Iron(III) fluoride
Names
Other names
iron trifluoride, ferric fluoride
Identifiers
7783-50-8 N
15469-38-2 (trihydrate) N
3D model (Jmol) Interactive image
ChemSpider 22958 YesY
ECHA InfoCard 100.029.093
PubChem 24552
RTECS number NO6865000
Properties
FeF3
Molar mass 112.840 g/mol (anhydrous)
166.89 g/mol (trihydrate)
Appearance pale green crystals
Density 3.87 g/cm3 (anhydrous)
2.3 g/cm3 (trihydrate)
Melting point > 1,000 °C (1,830 °F; 1,270 K)
slightly soluble (anhydrous)
49.5 g/100 mL (trihydrate)
Solubility negligible in alcohol, ether, benzene
Structure
Rhombohedral, hR24
R-3c, No. 167
Related compounds
Other anions
 iron(III) oxide, iron(III) chloride
Other cations
 manganese trifluoride, cobalt trifluoride, ruthenium(III) fluoride
Related compounds
 iron(II) 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

Iron(III) fluoride, also known as ferric fluoride, is an inorganic compound. It exists in an anhydrous form (formula FeF3) as well as two hydrated forms (both formula FeF3·3H2O). It is produced commercially mostly for laboratory work and is not as useful as the related compound iron(III) chloride. Anhydrous iron(III) fluoride is white while the hydrated forms are light pink.[1]

Chemical and physical properties

Iron(III) fluoride is a thermally robust, paramagnetic solid, consisting of high spin Fe(III) centers, which is consistent with the pale colors of all forms of this material. Both anhydrous iron(III) fluoride as well as its hydrates are hygroscopic.

Structure

The anhydrous form is adopts a simple structure with octahedral Fe(III)F6 centres interconnected by linear Fe-F-Fe linkages. In the language of crystallography, the crystals are classified as rhombohedral with an R-3c space group.[2] The structural motif is similar to that seen in ReO3. Although the solid is nonvolatile, it evaporates at high temperatures, the gas at 987 °C consists of FeF3, a planar molecule of D3h symmetry with three equal Fe-F bonds, each of length 176.3 pm.[3] At very high temperatures, it decomposes to give FeF2 and F2.[2]

Two crystalline forms—or more technically, polymorphs—of FeF3·3H2O are known, the α and β forms. These are prepared by evaporation of an HF solution containing Fe3+ at room temperature (α form) and above 50 °C (β form). The space group of the β form is P4/m, and the α form maintains a P4/m space group with a J6 substructure. The solid α form is unstable and converts to the β form within days. The two forms are distinguished by their difference in quadrupole splitting from their Mössbauer spectra.[4]

Preparation, occurrence, reactions

Anhydrous iron(III) fluoride is prepared by treating virtually any anhydrous iron compound with fluorine. More practically and like most metal fluorides, it is prepared by treating the corresponding chloride with hydrogen fluoride:[5]

FeCl3 + 3 HF → FeF3 + 3 HCl

It also forms as a passivating film upon contact between iron (and steel) and hydrogen fluoride.[6] The hydrates crystallize from aqueous hydrofluoric acid.[4]

The material is a fluoride acceptor. With xenon hexafluoride it forms [FeF4][XeF5].[2]

Applications

The primary commercial use of iron(III) fluoride in the production of ceramics.[7]

Some cross coupling reaction are catalyzed by ferric fluoride-based compounds. Specifically the coupling of biaryl compounds are catalyzed by hydrated iron(II) fluoride complexes of N-heterocyclic carbene ligands. Other metal fluorides also catalyse similar reactions.[8][9] Iron(III) fluoride has also been shown to catalyze chemoselective addition of cyanide to aldehydes to give the cyanohydrins.[10]

Safety

The anhydrous material is a powerful dehydrating agent. The formation of ferric fluoride may have been responsible for the explosion of a cylinder of fluorine gas.[11]

References

  1. ↑ Housecroft, Catherine E.; Sharpe, Alan G. (2008) Inorganic Chemistry (3rd ed.), Pearson: Prentice Hall. ISBN 978-0-13-175553-6.
  2. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
  3. ↑ Hargittai, M.; Kolonits, M.; Tremmel, J.; Fourquet. J.; Ferey, G. (January 1990). "The molecular geometry of iron trifluoride from electron diffraction and a reinvestigation of aluminum trifluoride". Structural Chemistry. 1 (1): 75–78. doi:10.1007/BF00675786.
  4. 1 2 Karraker, D. G.; Smith, P. K. (March 1992). "α- and β-FeF3•3H2O Revisited: Crystal Structure and 57Fe Mössbauer Spectra". Inorganic Chemistry. 31 (6): 1118–1120. doi:10.1021/ic00032a042.
  5. ↑ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 266-7.
  6. ↑ J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R. Romano, J. P. Cuer, "Fluorine Compounds, Inorganic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a11_307
  7. ↑ "Ferric Fluoride." CAMEO Chemicals. National Oceanic and Atmospheric Administration. Web. 7 Apr. 2010. <http://cameochemicals.noaa.gov/chemical/3468>
  8. ↑ Hatakeyama, T.; Nakamura M. (July 2007). "Iron-Catalyzed Selective Biaryl Coupling: Remarkable Suppression of Homocoupling by the Fluoride Anion". Journal of the American Chemical Society. 129 (32): 9844–9845. doi:10.1021/ja073084l. PMID 17658810.
  9. ↑ Hatakeyama, T.; Hashimoto, S.; Ishizuka, K.; Nakamura, M. (July 2009). "Highly Selective Biaryl Cross-Coupling Reactions between Aryl Halides and Aryl Grignard Reagents: A New Catalyst Combination of N-Heterocyclic Carbenes and Iron, Cobalt, and Nickel Fluorides". Journal of the American Chemical Society. 131 (33): 9844–9845. doi:10.1021/ja9039289. PMID 19639999.
  10. ↑ Bandgar, B. T.; Kamble, V. T. (July 2001). "Organic Reactions in aqueous medium: FeF3 catalyzed chemoselective addition of cyanotrimethylsilane to aldehydes". Green Chemistry. 3 (5): 265. doi:10.1039/b106872p.
  11. ↑ "A recent explosion of a lecture-size cylinder of hydrogen fluoride ... has renewed concerns that compressed gas cylinders can be especially dangerous." (PDF).
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