The protactinium(IV) halides
Protactinium tetrahalides, PaX4(X = Cl, Br, and I) have been prepared by reduction of the corresponding pentahalides by either aluminium or hydrogen at 400–450°. Protactinium tetrachloride and tetrabromide react with antimony trioxide at 200° in a vacuum to form the oxydihalides, PaOCl2 and PaOBr2, respectively. A pink residue which forms on sublimation of protactinium tetraiodide has been identified, by X-ray powder diffraction analysis, as the oxydi-iodide, PaOl2. Some chemical properties, visible spectra, and X-ray powder diffraction results are reported for these compounds and for protactinium tetrafluoride, PaF4.