Chromium(III) fluoride is the name for the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemi ...

s with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

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 r(H₂O)₆₃ and r(H₂O)₆₃•3H₂O are soluble in water. The trihydrate is green, and the hexahydrate is violet. The anhydrous form

sublimes Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...

at 1100–1200 °C.

Structures

Like almost all compounds of chromium(III), these compounds feature

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

Cr centres. In the anhydrous form, the six coordination sites are occupied by fluoride

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

s 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 Chromium(III) oxide (or chromia) is an inorganic compound with the formula . It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite. Structure and properties has the corundum ...

and

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepr ...

: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. :Cr₂O₃ + 6 HF + 9 H₂O → 2 r(H₂O)₆₃ 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 Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

of (NH₃)CrF₆: (NH₄)₃CrF₆ → CrF₃ + 3NH₃ + 3HF A mixed valence Cr₂F₅ is also known.

Uses

Chromium(III) fluoride finds some applications as a

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

in textiles and as a corrosion inhibitor. Chromium(III) fluoride catalyzes the fluorination of chlorocarbons by HF. 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.

References

Fluorides Metal halides Chromium(III) compounds {{inorganic-compound-stub