Some studies on uranium [V] halides and transition metal chalcogenide fluorides.
thesisposted on 19.11.2015, 08:47 by Garry Michael. Staunton
The early parts of this thesis are concerned with the preparation and some aspects of the chemistry of uranium pentafluoride. Reduction of UF6 is easily achieved but conditions are normally such that UF4 is the major product. Since fluorides with compositions intermediate between that of UF4 and UF6 have a reasonable stability, attempts were made to produce UF5 by the reduction of UF6. Good quality UF5 has been obtained by halogen exchange to produce UF5C1 and UF5Br which decomposes to give the pentafluoride. Attempts to prepare UF5 by reduction of UF6 by sulphur or Me3SiSiMe3 have also been made. The ability of UF5 to act as a Lewis acid has been reported, in reactions between UF5 and oxygen and nitrogen donor ligands. In the present work the reaction of UF5 with the oxygen donor ligands DMSO, acetone and 1,3- and 1,4-dioxane have been studies. The reaction of UF5 with 1,4-dioxane produced solid (UF5)2 (C4H8O2)3. Studies on the other systems clearly indicated that the chemistry of UF5 in non-aqueous media is dominated by side reactions which result in decomposition of the UF5. The ability of UF5 to act as a Lewis base has been previously demonstrated by the reaction of UF5 with SbF5 to produce UF5.2SbF5 and UF5.SbF5. In this study interaction of UF5 with NbF5 and TaF5 has been shown to give UF5.2MF5 and UF5.MF5 (M = Nb, Ta). These species being studied by vibrational spectroscopy, X-ray powder diffraction and thermal decomposition studies. It has also been shown that UF5 will react with AsF5 in the presence of anhydrous HF to produce UF5.ASF5, which is unstable at room temperature. In all cases it is probable that UF5 is acting as a Lewis base. It has also been demonstrated that BF3 is not a powerful enough Lewis acid to react with UF5. The reaction of UF5 with BiF5 was also examined, but the results were inconclusive, there being evidence both for adduct formation and oxidation of UF5 to UF6. Mixed chloride-fluorides of uranium (V) have been prepared by exchange reactions between Me3SiC1 and UF5, the mixed halides being isolated as complexes with triphenylphosphine or acetonitrile. These species were characterised by infrared spectroscopy, elemental analysis, X-ray powder diffraction, electronic spectroscopy and e.s.r. The final part of the thesis describes new techniques for the preparation of chalcogenide-fluorides of tungsten. The application of these techniques to the production of ReSF3, ReSF4 and ReSF5, as well as the attempted production of NbSF3, TaSF3 and USF4, are described. The new transition metal chalcogenide-fluorides produced were characterised by vibrational spectroscopy and mass spectrometry.