Preparation and structural characterization of α-NpF5

Until recently, only the pentafluorides of uranium and protactinium had been prepared, although thermodynamic calculations suggested NpF5 and possibly PuF5 should be stable. The synthesis of NpF5 by the oxidation of NpF4 in anhydrous hydrogen fluoride with KrF2 at room temperature has been reported recently. Analysis of this material by spectroscopic and analytical methods showed it to be NpF5. A new and relatively simple synthesis has been developed for UF5 by the reaction of UF6 dissolved in anhydrous hydrogen fluoride with excess PF3. A similar reaction has now been carried out with NpF6 with the resultant product being α-NpF5. Experimental details are given. The results of X-ray analysis are tabulated. All the lines in the powder pattern could be assigned on the basis of the α-UF5 structure. (U.K.)