It can also be obtained by reacting protactinium(V) oxide with aluminum bromide at 400 °C.[4]
Physical properties
Protactinium(V) bromide is an orange-red, crystalline, extremely moisture-sensitive solid that reacts violently with water and ammonia, but is persistent in absolutely dry air. It is insoluble in isopentane, dichloromethane and benzene, and in anhydrousacetonitrile is dissolves to form PaBr5•4CH3CN. It comes in several modifications. Below 400 °C as an α-modification and above 400 °C as a β-modification. The α-form has a monocliniccrystal structure of the space groupP21/c (No. 14) and lattice parametersa = 1296 pm, b = 1282 pm, c = 992 pm, β = 108° and the β-form also has monoclinic crystal structure with space group P21/n (No. 14, position 2) and lattice parameters a = 838.5 pm, b = 1120.5 pm, c = 895.0 pm, β = 91.1°.[3] The β form exists as a dimer. At 400 °C in a vacuum, protactinium(V) bromide sublimes.[5] A γ-form, which has a β-uranium(V) chloride-type crystal structure, has also been detected.[6]
^ abBrown, D.; Petcher, T. J.; Smith, A. J. (1969). "The crystal structure of β-protactinium pentabromide". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 25 (2): 178. Bibcode:1969AcCrB..25..178B. doi:10.1107/S0567740869007357.
^ abGeorg Brauer (Hrsg.), unter Mitarbeit von Marianne Baudler u. a.: Handbuch der Präparativen Anorganischen Chemie. 3., umgearbeitete Auflage. Band I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6, S. 1177.
^D. Brown, T. J. Petcher, A. J. Smith: The crystal structure of β-protactinium pentabromide. In: Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 25, S. 178–182, doi:10.1107/S0567740869007357.
^D. Brown: The polymorphism of protactinium pentabromide. In: Inorganic and Nuclear Chemistry Letters. 15, 1979, S. 219–223, doi:10.1016/0020-1650(79)80132-4.