The compound is made by reacting the elements in an acetonitrile solvent, or by reacting bromine with uranium metal or uranium tetrabromide at 55 °C (131 °F; 328 K).[1]
Uranium pentabromide is a hygroscopic dark brown solid that decomposes in water and most organic solvents, the exceptions being acetonitrileordichloromethane.[1] The compound is rather unstable and difficult to purify,[2] decomposing at 80 °C (176 °F; 353 K) into its constituent elements.[3] The crystal structure is the same as that of β-UCl5, which is triclinic and consists of U2Br10 dimers.[4]
Stable complexes of the form UBr5L are known with such ligandsastriphenylphosphine oxide and hexamethylphosphoramide, and are obtained by brominating UBr4 in the presence of the desired ligand.[2] In addition, it is possible to obtain a hexabromouranate(V) salt by reacting UBr5 with a monovalent bromide in thionyl bromide:[1]
