Several have been mentioned in the literature, but only the triiodide has been verified by X-ray crystallography.
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.
It is a black solid[3] produced by the reaction of osmium tetroxide and hydroiodic acid at 250 °C in nitrogen:[2] This compound decomposes in contact with water.
This black solid is produced by heating hexaiodoosmic acid(H2OsI6).
[4] However on attempted reproduction, this substance was found to be dihydroxonium hexaiodoosmate ((H3O+)2OsI62–).