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.

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.

Production
Chromium(III) fluoride is produced from the reaction of chromium(III) oxide and hydrofluoric acid:
 * Cr2O3 + 6 HF + 9 H2O → 2 [Cr(H2O)6]F3

The anhydrous form is produced from hydrogen fluoride and chromic chloride:
 * 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.

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.