Chromium(III) iodide, also known as chromium triiodide, is an inorganic compound with the formula . It is a black solid that is used to prepare other chromium iodides.
Like the isomorphous chromium(III) chloride (), chromium(III) iodide exhibits a cubic-closest packing arrangement in a double-layer crystal lattice. In this structure, chromium exhibits octahedral coordination geometry.
Chromium triiodide is prepared by the direct reaction of chromium metal with an excess of iodine. The reaction is conducted at 500 ðC:
To obtain high purity samples, the product is thermally decomposed at 700 ðC to sublime out chromium(II) iodide. The diiodide is then reiodinated.
Chromium triiodide is stable in contact with oxygen and moisture, but at temperatures approaching 200 ðC it reacts with oxygen and releases iodine. Like , 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.
Chromium triiodide can also be prepared as colloidal nanoplatelets, a type of lateral nanostructure. The alkoxide is dissolved in toluene under an inert atmosphere, followed by the addition of trimethylsilyl iodide. The mixture is sealed and immersed into a preheated oil bath at 135 ðC, resulting in the formation of a black precipitate.
Chromium triiodide was one of the first materials which was discovered to be a magnetic two-dimensional material that has great potentials for spintronics devices.