Studies on inorganic oxide fluorides.
thesisposted on 19.11.2015, 08:46 by David. Laycock
Uranium oxide tetrafluoride reacts with the Lewis acid pentafluorides BiF5, NbF5 and TaF5 to produce the fluorine-bridged adducts UOF4. 2BiF5, UOF4. 3NbF5 and UOF4. 3TaF5. These complexes have been prepared by the reactions of UOF4 with the pentafluorides in anhydrous hydrofluoric acid solvent or by fusing together UOF4/MF5 mixtures. They have been characterized by elemental analysis, vibrational spectroscopy and X-ray powder diffraction and it has been shown that, in these complexes, UOF4 possesses fluoride-ion donor properties. The first examples of compounds formed between uranyl fluoride and a Lewis acid pentafluoride are reported. The reaction of anhydrous UO2F2 with SbF5 in anhydrous HF produces UO2F2. 3SbF5 which, on heating in vacuo at 125C, gives UO2F2. 2SbF5. On heating to 245C this 1:2 adduct loses both SbF5 ligands simultaneously to produce anhydrous UO2F2. The crystal structure of the 1:3 adduct has been determined from single-crystal X-ray studies which have shown it to be a fluorine bridged network. The structure can be described in terms of zig-zag chains of UO2 groups linked to SbF6 units with Sb2F11 units attached as side-chains to the uranium with significant ionic contributions to the bondings. Solutions of UOF4 with SbF5 in anhydrous HF are unstable for periods of longer than a few hours at room temperature. On standing these orange solutions lose their colour and crystals of uranium hexafluoride appear. The reaction seems to produce a uranyl fluoride - antimony pentafluoride complex but this has not been fully characterized. Xenon difluoride reacts violently with iodine dioxide trifluoride at room temperature to give XeF2. IF5 and IO2F. However, a Raman study has shown that, if the reaction is controlled by employing low-temperature procedures, XeF2/IO2F3 complexes are formed. The ternary adducts UOF4. mSbF5. nCH3CN (m = l, 2; n = 2, 6 respectively) and UF5.xSbF5. yCH3CN (x = l, 2; y = 2, 5 respectively) have been prepared by the reaction of dry acetonitrile with the appropriate binary adduct.