Uranium pentabromideUranium pentabromide is an inorganic chemical compound with the formula.SynthesisThe compound is made by reacting the elements in an acetonitrile solvent, or by reacting bromine with uranium metal or uranium tetrabromide at.PropertiesUranium pentabromide is a hygroscopic dark brown solid that decomposes in water and most organic solvents, the exceptions being acetonitrile or dichloromethane. The compound is rather unstable and difficult to purify, decomposing at into uranium tetrabromide and bromine. The crystal structure is the same as that of β-[uranium pentachloride|], which is triclinic and consists of dimers.ComplexesStable complexes of the form are known with such ligands as triphenylphosphine oxide and hexamethylphosphoramide, and are obtained by brominating in the presence of the desired ligand. In addition, it is possible to obtain a hexabromouranate salt by reacting with a monovalent bromide in thionyl bromide: