Osmium iodides explained

Osmium iodide refers to compounds of osmium with the formula OsI_n. Several have been mentioned in the literature, but only the triiodide has been verified by X-ray crystallography.^[1]

Osmium(I) iodide

Osmium(I) iodide is the iodide of osmium with the formula OsI. It is a metallic grey solid produced by the reaction of osmium tetroxide and hydroiodic acid heated in a water bath for 48 hours in a carbon dioxide atmosphere. This compound is amorphous.

Osmium(II) iodide

Osmium(II) iodide is the iodide of osmium with the formula OsI₂. It is a black solid produced by the reaction of osmium tetroxide and hydroiodic acid at 250 °C in nitrogen:

OsO₄ + HI → OsI₂ + H₂OThis compound decomposes in contact with water.^[2]

Osmium(III) iodide

Osmium(III) iodide is the iodide of osmium with the formula OsI₃. This black solid is produced by heating hexaiodoosmic acid(H₂OsI₆). This compound is insoluble in water.

Osmium(IV) iodide

What was claimed to be osmium(IV) iodide was produced by the reaction of osmic acid (H₄OsO₆) and hydroiodic acid.^[3] However on attempted reproduction, this substance was found to be dihydroxonium hexaiodoosmate ((H₃O⁺)₂OsI₆^2–). When heated this did not form a tetraiodo compound, and instead formed mono, di, and tri-iodo osmium compounds.^[4]

Notes and References

1. Book: 10.1002/9781119951438.eibc0078.pub2. Halides: Solid-State Chemistry. Encyclopedia of Inorganic and Bioinorganic Chemistry. 2014. Köhler. J.. 1–22. 9781119951438.
2. Book: George K. Schweitzer . Lester L. Pesterfield . George K. Schweitzer . The Aqueous Chemistry of the Elements . 2009 . Oxford University Press . 9780199742196 . 321 . 11 November 2021 . en . Ebook.
3. News: The Chemistry of Osmium . the Sciences . Scientific American . 1893 . 35 . 904supp . 14453–14454 . 10.1038/scientificamerican04291893-14453supp.
4. Fergusson . J. E. . Robinson . B. H. . Roper . W. R. . 405. Iodides of osmium and rhenium . Journal of the Chemical Society (Resumed) . 1962 . 2113 . 10.1039/JR9620002113.