RYSTAL STRUCTURE DETERMINATION

Uranium pentafluoride prepared in the above maimer is the low-temperature, form, which can be identified by its characteristic X-ray powder pattern. The single<rystal structure has been determined tetragonal symmetry, space group I42d(Z = 8), with eight-coordination and a geometry intermediate between a dodecahedron and a square antiprism. Uranium pentafluoride is air sensitive and disproportionates in water to give a precipitate of uranium tetrafluoride and a solution of uranyl fluoride. Consequently, UFs must be handled in an inert atmosphere. The near-infrared-visible spectrum of uranium pentafluoride in acetonitrile has been determined and is perhaps the most convenient characterization. 

Because of anomalous scattering by H, the results for the as-precipitated Ni(OH)2 could not be refined. Nevertheless, cell constants and the O-H bond distance could be determined. The results showed that the as-precipitated material was different from the well-crystaUized material. The unit cell dimensions were ao = 3.119 A and Co = 4.686 A. Also the O-H bond length was 1.08 A, a value similar to that previously reported by Szytula et al. in a neutron diffraction study of Ni(OH)2 [23]. The O-H bond in both well-crystalhzed and as-precipitated materials is parallel to the c-axis. The difference between wellelectrochemically active. The differences between the materials are attributed to a defective structure that arises from the large concentration of surface OH ion groups in the high-surface-area material [22]. These are associated with absorbed water. This is a consistent with an absorption band in the infrared at 1630 cm . This is not seen in the well-crystallized material. 

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