Chromium(II) iodide explained

Chromium(II) iodide is the inorganic compound with the formula CrI₂. It is a red-brown or black solid. The compound is made by thermal decomposition of chromium(III) iodide. Like many metal diiodides, CrI₂ adopts the "cadmium iodide structure" motif, i.e., it features sheets of octahedral Cr(II) centers interconnected by bridging iodide ligands. Reflecting the effects of its d⁴ configuration, chromium's coordination sphere is highly distorted.^{[1] [2]}

Treatment of chromium powder with concentrated hydroiodic acid gives a blue hydrated chromium(II) iodide, which can be converted to related acetonitrile complexes.^[3]

Cr + nH₂O + 2HI → CrI₂(H₂O)_n + H₂

Notes and References

1. 10.1107/S0365110X62001152. The Crystal Structure of Chromium(II) Iodide. 1962. Tracy. J. W.. Gregory. N. W.. Stewart. J. M.. Lingafelter. E. C.. Acta Crystallographica. 15. 5. 460–463.
2. 10.1021/ic901949a. Nucleation of Antiferromagnetically Coupled Chromium Dihalides: From Small Clusters to the Solid State. 2010. Vest. Brian. Hermann. Andreas. Boyd. Peter D. W.. Schwerdtfeger. Peter. Inorganic Chemistry. 49. 7. 3169–3182.
3. 10.1002/9780470132418.ch4. Chromium(II) Salts and Complexes. Inorganic Syntheses. 1967. Holah. David G.. John P. Fackler Jr.. Fackler. John P.. 26–35.