Chromium triiodide, chromic iodide
|3D model (Jmol)||Interactive image|
|Molar mass||432.710 g/mol|
|Melting point||> 600 °C (1,112 °F; 873 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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.
- Perry, Dale L. (2011). Handbook of Inorganic Compounds, Second Edition. Boca Raton, Florida: CRC Press. p. 123. ISBN 978-1-43981462-8. Retrieved 2014-01-10.
- Gregory, N. W., Handy, L. L. "Chromium(III) iodide" Inorg. Synth. 1957, vol. 5, 128-130. doi:10.1002/9780470132364.ch34
- Gregory, N. W.; Handy, L. L. (1952). "Structural Properties of Chromium(III) Iodide and Some Chromium(III) Mixed Halides". J. Am. Chem. Soc. 74: 891–893. doi:10.1021/ja01124a009.