The preparation and crystal structures of some metal fluoride complexes.
thesisposted on 19.11.2015, 08:44 by John. Fawcett
The preparation of the adducts formed between antimony pentafluoride and the oxide tetrafluorides of uranium, molybdenum, tungsten and rhenium is described. Structural details from full single crystal X-ray investigations are reported for the adducts UF4O. 2SbF5 and MF4O.SbF5 (M = Mo or Re). The rhenium adduct forms discrete fluorine bridged rings of the dimer 2(ReF40.SbF5), the molybdenum adduct has a polymeric zig-zag chain arrangement, and the UF4O. 2SbF5 structure contains both the ring and chain units in a three-dimensional network. Crystallographic and vibrational spectroscopic evidence indicate a small ionic contribution in the bridging bonds. The structures of three complex fluorides of the form A1BVF6, previously studied by X-ray powder diffraction, have been redetermined. NaTaF6 and a new triclinic form of (?-) CsNbF6 were studied by X-ray single crystal methods, and NaWf6, by refinement of data from neutron diffraction of the microcrystalline powder. The NaTaF6 structure is found to be consistent with the previously described face centred cubic (NaSbF6) type, however, the NaWF6 structure has been reassigned as primitive cubic (Pa3). Structures of two complex Quorides of the A12BivF6 general form are reported. (NH4)2PtF6 was found to be of the face centred cubic (K2SiF6) type and K2OsF6 of the trigonal (K2GeF6) type. Three structures are described that are considered as incomplete due to unsatisfactory refinement of the fluorine atom positions in apparently disordered structures. For NF4.SbF6, difficulty was encountered in the refinement of fluorine atom positional parameters about the antimony atom. Similar problems were encountered in the location of the fluorine atoms of the hydroxonium salts H3O.MF6 (M=Sb or Ta). Finally the preparation and crystal structure of WF5N3, the first azide derivative of a transition metal fluoride are reported. Unsuccessful attempts to isolate M0F5N3 and WF6-n(N3)n (n>2) are also described.