The preparation of pure, solvent-free uranium tetrahalides often requires harsh conditions and can need metallic uranium, which is hard to access, especially in a pure form. Additionally, there are no easy lab-scale methods to purify starting materials such as uranium metal or uranium oxides.

Stefan S. Rudel and Florian Kraus, University of Marburg, Germany, have developed an alternative synthesis for UCl₄, UBr₄, and UI₄ which uses readily available uranyl salts such as UO₂(NO₃)₂·6 H₂O as a starting material. This salt was decomposed and reduced with H₂ at 700–800 °C to give UO₂. The resulting oxide was then reacted with aluminum halides (AlCl₃, AlBr₃, or AlI₃) in a sealed ampoule at 150–300°C to give the desired uranium halides. The products could be purified in situ using chemical vapor transport by applying a temperature gradient to the ampoule.

After two to eight days of transport within the temperature gradient, the researchers obtained crystalline aggregates of pure uranium tetrahalides. The products were synthesized in amounts of up to eight grams and their purity was confirmed using X-ray diffraction, infrared (IR) spectroscopy, and elemental analyses. The approach is simple, tolerates impurities in the UO₂, and does not need a complex apparatus.

• Facile syntheses of pure uranium halides: UCl₄, UBr₄ and UI₄,
  Stefan S. Rudel, Florian Kraus,
  Dalton Trans. 2017.
  DOI: 10.1039/c7dt00726d