Uranium Tetrabromide, UBr₄

Uranium Tetrabromide, Uranous Bromide, UBr₄, is prepared by passing a mixture of nitrogen or carbon dioxide and bromine vapour over a heated mixture of urano-uranic oxide and charcoal. The product may be purified by sublimation in absence of air. It may also be prepared by heating fused uranous chloride in a current of hydrogen bromide. The bromide is deposited as a sublimate consisting of lustrous dark brown leaflets, of density 4.838 at 21° C. At red heat it yields a dark brown vapour of density 19.46 (air = l), corresponding to a molecular weight 536.6. The theoretical value for UBr₄ is 557.9. Uranous bromide is hygroscopic and very soluble in water, but the solution resembles that of uranous chloride in being unstable; hydrogen bromide escapes, and by oxidation yellow uranyl bromide is formed.

Double bromides of the type R₂UBr₆, similar to the corresponding chlorides, have been prepared by passing uranium tetrabromide vapour over the heated alkali bromides. The potassium and sodium salts, K₂UBr₆ and Na₂UBr₆, are green crystalline substances, hygroscopic, but less so than uranium tetrabromide.