Chromium(III) fluoride explained

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

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.^[1]

Production

Chromium(III) fluoride is produced from the reaction of chromium(III) oxide and hydrofluoric acid:^[2]

The anhydrous form is produced from hydrogen fluoride and chromic chloride:^[3]

Another method of synthesis of involves thermal decomposition of (ammonium hexafluorochromate(III)):

A mixed valence compound (chromium(II,III) fluoride) is also known.^[4]

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.^{[5] [6]}

References

1. 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
2. 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.
3. Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. .
4. Sturm. B.J. Phase Equilibria in the System Chromium(II)Fluoride-Chromium(III) Fluoride. Inorg. Chem., 1962, 1 (3), pp 665–672
5. Mallikarjuna R. V. N.; Subramanian M. A. Fluoroolefin Manufacturing U.S. Patent 6,031,14, August 6, 1998; n.a.
6. 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.