Chromium(III) bromide

Chromium(III) bromide

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Names
IUPAC name Chromium(III) bromide
Other names Chromium tribromide, Chromium bromide, Chromic bromide
Identifiers
CAS Number	10031-25-1 13478-06-3 (hexahydrate)
ChemSpider	74280
EC Number	233-088-6
Jmol 3D model	Interactive image
PubChem	82309
InChI InChI=1S/3BrH.Cr/h3*1H;/q;;;+3/p-3 Key: UZDWIWGMKWZEPE-UHFFFAOYSA-K
SMILES [Cr+3].[Br-].[Br-].[Br-]
Properties
Chemical formula	CrBr3
Molar mass	291.71 g/mol
Appearance	Black lustrous crystals; green in transmitted light, reddish in reflected light
Density	4.25 g/cm3
Melting point	1,130 °C (2,070 °F; 1,400 K) (anhydrous) 79 °C (hexahydrate)
Solubility in water	insoluble in cold water, soluble with addition of Chromium(II) ion salts, soluble in hot water
Structure
Crystal structure	trigonal
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chromium(III) bromide is an inorganic compound with the chemical formula CrBr₃. It is a dark colored solid that appears green in transmitted light but red with reflected light. It is used as a precursor to catalysts for the oligomerization of ethylene.

Synthesis

The compound is prepared in a tube furnace by the reaction of bromine vapor and chromium powder at 1000 °C. It is purified by extracting with absolute diethyl ether to remove any CrBr₂, and is subsequently washed with absolute diethyl ether and absolute ethanol.

Analogous to the behavior of related chromium(III) halides, the tribromide dissolves in water to give CrBr₃(H₂O)₃ only upon the addition of catalytic amounts of a reducing agent, which generates CrBr₂. The reducing agent generates chromous bromide on the surface of the solid, which dissolves and re-doxidizes to Cr(III).