Sublimation: technique under reduced pressure

The hexachloride, uranium hexachloride [13763-23-0], UCl, is best prepared by chlorination of UCl [10026-10-5] with SbCl. An alternative preparative approach is the disproportionation UCl [13470-21 -8] to UCl and UCl under reduced pressure. The obvious disadvantage of the second method is contamination by UCl, however, sublimation is a possible purification technique. Isostmctural with the hexafluoride, the hexachloride is monomeric with an octahedral arrangement of the chlorine atoms around the uranium center. 

One of the most useful and convenient techniques for the purification of solids is sublimation. In this process, the solid is warmed (often under reduced pressure) until its vapor pressure becomes high enough for it to collect on a cooled surface placed above the solid. Sublimation is limited to compounds which have reasonably high vapor pressures and which pass directly from the solid state to the vapor. However, the process involving initial melting followed by vaporization and deposition on the condenser may be carried out in the same apparatus and is often loosely called sublimation. 

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