Structures of fluorides XIII: the orthorhombic form of tungsten hexafluoride at 193/sup 0/K by neutron diffraction

Journal Article · Wed Jan 01 00:00:00 EST 1975 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(75)90292-3· OSTI ID:6468994

Levy, J H; Taylor, J C; Wilson, P W

The positional parameters in the orthorhombic phase of solid tungsten hexafluoride WF/sub 6/ have been determined by total profile analysis of a neutron powder pattern taken at 193/sup 0/K. WF/sub 6/ at 193/sup 0/K is orthorhombic, with space group Pnma(D/sub 2h//sup 16/) and a = 9.603 (3), b = 8.713 (4), and c = 5.044 (3) A at 193/sup 0/K. The full matrix, least-squares refinement converged at R = ..sigma..(abs. value y/sub 0/ - (1/c)y/sub c/ abs. value)/..sigma.. y/sub 0/ = 0.075 where c is the scale factor and y/sub 0/ is one of the 306 background-corrected intensities in range of one or more Bragg reflections along the pattern. The refinement showed that, at this temperature, WF/sub 6/ has the orthorhombic UF/sub 6/ structure. The mean W-F distance is 1.81 A, and the mean F-F separation between octahedra is 3.12 A. The results are compared with previous neutron profile studies of the orthorhombic phases of UF/sub 6/ and MoF/sub 6/ at 193/sup 0/K, and with a neutron profile Kubic Harmonic analysis of the cubic form of WF/sub 6/ at 266/sup 0/K. On the basis of these structural studies in this series of hexafluorides, reasons are given why MoF/sub 6/ and WF/sub 6/ have a high-temperature cubic phase, but UF/sub 6/ does not. Deviations from idealized h.c.p. coordinates in the orthorhombic phases are in a direction such that the fluorine atoms become strongly bonded to the metal atoms to form a molecular, rather than an ionic, lattice. 2 figures, 5 tables.

• Research Organization: Australian Atomic Energy Commission, Sutherland
• OSTI ID: 6468994
• Journal Information: J. Solid State Chem.; (United States), Vol. 15
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
TUNGSTEN FLUORIDES
ORTHORHOMBIC LATTICES
STRUCTURAL CHEMICAL ANALYSIS
BRAGG REFLECTION
LOW TEMPERATURE
MOLYBDENUM FLUORIDES
NEUTRON DIFFRACTION
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
MOLYBDENUM COMPOUNDS
REFLECTION
SCATTERING
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
400201* - Chemical & Physicochemical Properties