Chromium(III) fluoride

Chromium(III) fluoride is an inorganic compound with the chemical formula CrF₃. It forms several hydrates. The compound CrF₃ is a green crystalline solid that is insoluble in common solvents, but the hydrates [Cr(H₂O)₆]F₃ (violet) and [Cr(H₂O)₆]F₃·3H₂O (green) are soluble in water. The anhydrous form sublimes at 1100–1200 °C.^[3]

Chromium(III) fluoride

Names
IUPAC name Chromium(III) fluoride
Other names Chromium trifluoride
Identifiers
CAS Number	7788-97-8 Y 16671-27-5 (trihydrate) 123333-98-2 (tetrahydrate)
3D model (JSmol)	Interactive image
ChemSpider	8329529 Y
ECHA InfoCard	100.029.216
PubChem CID	10154021
RTECS number	GB6125000
UNII	YK57ASE6UA Y
CompTox Dashboard (EPA)	DTXSID10880971
InChI InChI=1S/Cr.3FH/h;3*1H/q+3;;;/p-3 Y Key: FTBATIJJKIIOTP-UHFFFAOYSA-K Y InChI=1/Cr.3FH/h;3*1H/q+3;;;/p-3 Key: FTBATIJJKIIOTP-DFZHHIFOAR
SMILES [Cr+3].[F-].[F-].[F-]
Properties
Chemical formula	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)
Solubility in water	negligible (anhydrous) sparingly soluble (trihydrate)
Solubility	Insoluble in alcohols Soluble in HF, HCl
Magnetic susceptibility (χ)	+4370.0·10−6 cm3/mol
Structure
Crystal structure	Rhombohedral, hR24
Space group	R-3c, No. 167
Hazards
Lethal dose or concentration (LD, LC):
LD50 (median dose)	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). Y verify (what is YN ?) 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 [NH₄]₃[CrF₆] (ammonium hexafluorochromate(III)):

[NH₄]₃[CrF₆] → CrF₃ + 3 NH₃ + 3 HF

A mixed valence compound Cr₂F₅ (chromium(II,III) fluoride) 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 or 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.