Chromium(III) fluoride

Chromium(III) fluoride is the name for the inorganic compounds with the chemical formula CrF3 as well as several related hydrates. The compound CrF3 is a green crystalline solid that is insoluble in common solvents, but the coloured hydrates [Cr(H2O)6]F3 and [Cr(H2O)6]F3•3H2O are soluble in water. The trihydrate is green, and the hexahydrate is violet. The anhydrous form sublimes at 1100–1200 °C.[3]

Chromium(III) fluoride
Names
IUPAC name
Chromium(III) fluoride
Other names
Chromium trifluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.216
RTECS number
  • GB6125000
UNII
Properties
CrF3
Molar mass 108.9913 g/mol (anhydrous)
163.037 g/mol (trihydrate)
181.05 g/mol (tetrahydrate)
Appearance green crystalline solid
Density 3.8 g/cm3 (anhydrous)
2.2 g/cm3 (trihydrate)
Melting point 1,100 °C (2,010 °F; 1,370 K) (sublimes)
negligible (anhydrous)
sparingly soluble (trihydrate)
Solubility insoluble in alcohols
soluble in HF, HCl
+4370.0·10−6 cm3/mol
Structure
Rhombohedral, hR24
R-3c, No. 167
Hazards
Lethal dose or concentration (LD, LC):
150 mg/kg (guinea pig, oral)[1]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3[2]
REL (Recommended)
 TWA 0.5 mg/m3[2]
IDLH (Immediate danger)
 250 mg/m3[2]
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

Structures

Like almost all compounds of chromium(III), these compounds feature octahedral Cr centres. In the anhydrous form, the six coordination sites are occupied by fluoride ligands that bridge to adjacent Cr centres. In the hydrates, some or all of the fluoride ligands are replaced by water.[4]

Production

Chromium(III) fluoride is produced from the reaction of chromium(III) oxide and hydrofluoric acid:[5]

Cr2O3 + 6 HF + 9 H2O → 2 [Cr(H2O)6]F3

The anhydrous form is produced from hydrogen fluoride and chromic chloride:[6]

CrCl3 + 3 HF → CrF3 + 3 HCl

Another method of synthesis of CrF3 involves thermal decomposition of (NH3)CrF6: (NH4)3CrF6 → CrF3 + 3NH3 + 3HF A mixed valence Cr2F5 is also known.[7]

Uses

Chromium(III) fluoride finds some applications as a mordant in textiles and as a corrosion inhibitor. Chromium(III) fluoride catalyzes the fluorination of chlorocarbons by HF.[8] [9]

References
  1. "Chromium(III) compounds [as Cr(III)]". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  2. NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
  3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  4. F.H. Herbstein, M. Kapon and G.M. Reisner, "Crystal structures of chromium(III) fluoride trihydrate. Structural chemistry of hydrated transition metal fluorides. Thermal decomposition of chromium(III) fluoride nonhydrate" Zeitschrift für Kristallographie 1985, volume 171, pp. 209
  5. Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a07_067
  6. Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
  7. Sturm. B.J. Phase Equilibria in the System Chromium(II)Fluoride-Chromium(III) Fluoride. Inorg. Chem., 1962, 1 (3), pp 665–672
  8. Mallikarjuna R. V. N.; Subramanian M. A. Fluoroolefin Manufacturing U.S. Patent 6,031,14, August 6, 1998; n.a.
  9. Ruh R. P.; Davis R. A. Proceess for Fluorinating Aliphatic Halohydrocarbons with a Chromium Fluoride catalyst and process for preparing the catalyst. U.S. Patent 2,745,886, May 15, 1956; n.a.
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