Osmium iodides

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][2]

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.^[2]

Osmium(II) iodide

Solution of OsI₂•2HI

Osmium(II) iodide is the iodide of osmium with the formula OsI₂. It is a black solid^[3] produced by the reaction of osmium tetroxide and hydroiodic acid at 250 °C in nitrogen:^[2]

OsO₄ + HI → OsI₂ + H₂O

This compound decomposes in contact with water.^[3]

When a solution of osmium tetroxide in hydrochloric acid is reduced with potassium iodide, so-called osmium hydroiodide (OsI₂•2HI) is formed,^[4][5] which possesses a strong green color. It reacts with oxidizers such as hypoiodites to yield osmates.

OsO₄ + 10HCl + 10KI → OsI₂•2HI + 4H₂O + 10KCl + 3I₂

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).^[2] This compound is insoluble in water.^[3]

Osmium(IV) iodide

What was claimed to be osmium(IV) iodide was produced by the reaction of osmic acid (OsO₂•2H₂O) and hydroiodic acid.^[6] 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.^[2]