[3] It can also be obtained by reacting protactinium(V) oxide with aluminum bromide at 400 °C.

[4] 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 anhydrous acetonitrile is dissolves to form PaBr5•4CH3CN.

The α-form has a monoclinic crystal structure of the space group P21/c (No.

[5] A γ-form, which has a β-uranium(V) chloride-type crystal structure, has also been detected.