Chromium(III) iodide

Chromium(III) iodide

Names
IUPAC name Chromium(III) iodide
Other names Chromium triiodide, chromic iodide
Identifiers
CAS Number	13569-75-0
ChemSpider	75416
Jmol 3D model	Interactive image
PubChem	83586
InChI InChI=1S/Cr.3HI/h;3*1H/q+3;;;/p-3 Key: PPUZYFWVBLIDMP-UHFFFAOYSA-K InChI=1/Cr.3HI/h;3*1H/q+3;;;/p-3/rCrI3/c2-1(3)4 Key: PPUZYFWVBLIDMP-GXOYXQMQAU
SMILES [Cr](I)(I)I
Properties
Chemical formula	CrI3
Molar mass	432.710 g/mol
Appearance	black solid
Density	5.32 g/cm3
Melting point	> 600 °C (1,112 °F; 873 K)
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) iodide, also known as chromium triiodide, is an inorganic compound with the formula CrI₃. It is a black solid that is used to prepare other chromium compounds.

Being isomorphous with chromium(III) chloride (CrCl₃), it exhibits a cubic-closest packing arrangement in a double-layer crystal lattice. In this structure, chromium exhibits octahedral coordination geometry.

Preparation and properties

Chromium triiodide is prepared by the direct reaction of chromium metal with an excess of iodine. The reaction is conducted at 500 °C:

2 Cr + 3 I₂ → 2 CrI₃

To obtain high purity samples, the product is thermally decomposed at 700 °C to sublime out chromium(II) iodide. The diiodide is then reiodinated.

At room temperature, chromium triiodide is stable in contact with oxygen and moisture, but at temperatures approaching 200 °C it reacts with oxygen and releases iodine. Like CrCl₃, the triiodide exhibits slow solubility in water owing to the kinetic inertness of Cr(III). Addition of small amounts of chromous iodide accelerates the dissolving process.