Bromides of Osmium

Osmium is not affected by exposure to bromine vapour even under the influence of heat. By warming osmic acid, H₂OsO₄, with hydrobromic acid in the presence of alcohol (to prevent oxidation to the volatile tetroxide), a brown solution was obtained by Moraht and Wischin. This was concentrated in vacuo over sulphuric acid and potassium hydroxide, the latter to absorb the hydrobromic acid, and upon recrvstallisation dark reddish brown hygroscopic needles were obtained. These were readily soluble in water and alcohol, from which they could be recrystallised unchanged in the cold. The results of analysis agreed well with the formula Os₂Br₉.6H₂O, indicating, probably, a mixture of the tri- or tetra- bromide with some higher bromide. Concentration of the solution on the water-bath results in the formation of an oxybromide of unknown constitution.