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A Powder Neutron-Diffraction Determination of the Structure of Ba 4 Sb 3 LiO ~ z : the Preparation and Structure of the Perovskite-Related Compounds Ba 4 M 3 LiO 12 ( M = Sb , Bi ) and BasM 3
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2001 |
| Abstract | (Edwards & Jones, 1968b) of WOF4 found the structural unit to be a tetramer, [WF402/214, with the tungsten atoms approximately at the corners of a square and bridging W O W bonds. However the infrared and Raman spectra strongly suggest terminal W = O bonds and bridging fluorine atoms (Beattie, Livingston, Reynolds & Ozin, I970; Beattie & Reynolds, I968; Winfield, 1972). The X-ray result is clearly a 'correct' structure in the sense that the centres of the electron density distribution were located. On close examination, it appears that it is impossible to propose an ordered structure with fluorine bridging and satisfy the valence requirements of W within the symmetry of the possible space groups, C2/m, C2 and 6',,. This, together with the spectral evidence, enforces the conclusion that there must be O, F disorder in the WOF4 crystal studied by Edwards & Jones (1968b). By analogy with ordered ReOF4 (Edwards & Jones, 1968a), which X-ray analysis indicates is fluorine-bridged, the O-F disorder is probably mainly in the shorter in-plane terminal bonds. We have refined a disordered model with the published X-ray data for WOF4, but failed to obtain a significantly lower R value for the disordered model. Difference maps were also inconclusive, and more accurate data would appear necessary for a clear demonstration of the possible disorder in WOF4. Polymorphism has been found in other oxide tetrafluorides. TcOF4 has a blue monoclinic form (Edwards, Jones & Sills, 1968) with a structure similar to VFs and a green hexagonal form comprising the cyclic tetramers [TcOF3F2/2]. MoOF4 also has a similar dimorphism (Edwards, Jones & Sills, 1968) but the hexagonal form changes to the monoclinic form in a few days. The structure of ~-UOF4 is presently being studied in this laboratory. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://journals.iucr.org/b/issues/1974/07/00/a11135/a11135.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
