Iron(III) fluoride

Iron(III) fluoride, also known as ferric fluoride, are inorganic compounds with the formula FeF3(H2O)x where x = 0 or 3. They are mainly of interest by researchers, unlike the related iron(III) chloride. Anhydrous iron(III) fluoride is white, whereas the hydrated forms are light pink.[2]

Iron(III) fluoride
Names
Other names
iron trifluoride, ferric fluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.093
RTECS number
  • NO6865000
UNII
  • InChI=1S/3FH.Fe/h3*1H;/q;;;+3/p-3 checkY
    Key: SHXXPRJOPFJRHA-UHFFFAOYSA-K checkY
  • InChI=1/3FH.Fe/h3*1H;/q;;;+3/p-3
    Key: SHXXPRJOPFJRHA-DFZHHIFOAS
  • F[Fe](F)F
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
+13,760·10−6 cm3/mol
Structure
Rhombohedral, hR24
R-3c, No. 167
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive
GHS labelling:
GHS05: Corrosive GHS07: Exclamation mark[1]
Danger[1]
H302, H312, H314, H332[1]
P260, P301+P330+P331, P303+P361+P353, P305+P351+P338, P405, P501[1]
Safety data sheet (SDS) External SDS
Related compounds
Other anions
 Iron(III) oxide, Iron(III) chloride
Other cations
 Manganese(III) fluoride, Cobalt(III) fluoride, 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

Chemical and physical properties

Iron(III) fluoride is a thermally robust, antiferromagnetic[3] 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 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.[4] 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.[5] At very high temperatures, it decomposes to give FeF2 and F2.[4]

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.[6]

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:[7]

FeCl3 + 3 HF → FeF3 + 3 HCl

It also forms as a passivating film upon contact between iron (and steel) and hydrogen fluoride.[8] The hydrates crystallize from aqueous hydrofluoric acid.[6]

The material is a fluoride acceptor. With xenon hexafluoride it forms [FeF4][XeF5].[4]

Pure FeF3 is not yet known among minerals. However, hydrated form is known as the very rare fumarolic mineral topsøeite. Generally a trihydrate, its chemistry is slightly more complex: FeF[F0.5(H2O)0.5]4·H2O.[9][10]

Applications

The primary commercial use of iron(III) fluoride in the production of ceramics.[11]

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.[12][13] Iron(III) fluoride has also been shown to catalyze chemoselective addition of cyanide to aldehydes to give the cyanohydrins.[14]

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 hydrogen fluoride gas.[15]

References
  1. "Iron(III) Fluoride". American Elements. Retrieved November 5, 2018.
  2. Housecroft, Catherine E.; Sharpe, Alan G. (2008) Inorganic Chemistry (3rd ed.), Pearson: Prentice Hall. ISBN 978-0-13-175553-6.
  3. Wollan, E. O.; Child, H. R.; Koehler, W. C.; Wilkinson. M. K. (November 1958). "Antiferromagnetic properties of the iron group trifluorides". Physical Review. 112 (4): 1132–1136. Bibcode:1958PhRv..112.1132W. doi:10.1103/PhysRev.112.1132.
  4. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  5. 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. S2CID 96178006.
  6. 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.
  7. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 266-7.
  8. 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
  9. "Topsøeite".
  10. "List of Minerals". 21 March 2011.
  11. "Ferric Fluoride." CAMEO Chemicals. National Oceanic and Atmospheric Administration. Web. 7 Apr. 2010. <http://cameochemicals.noaa.gov/chemical/3468>
  12. 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.
  13. 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.
  14. 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.
  15. "A recent explosion of a lecture-size cylinder of hydrogen fluoride ... has renewed concerns that compressed gas cylinders can be especially dangerous" (PDF). University of California San Francisco. Archived from the original (PDF) on 2006-09-01.
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