X-Ray Diffraction Studies of Some Transition Metal Hexafluorides

Abstract

Crystallographic studies are presented for the transition metal hexafluorides MoFs, TcFB, RuFs, RhFs, WFs, ReFe, OsF6, IrFG, and PtF6. Each exhibits a cubic modification near room temperature and a phase of lower symmetry, probably orthorhombic, a t reduced temperatures.XRay results are presented for ReF7, which also exhibits a cubic phase a t room temperature and a second modification a t a very low temperature.Unit cell sizes for both phases as well as transition temperatures are given.

The origin of the crystallographic pedigree

“…The M3M' alloys with rare earths M' randomly distributed in 4(a)O h show the pedigree as shown in Table 5 (Siegel & Northrop, 1966) as the C2X 6 compounds with X = H, F, C1, Br and Me and C2H 4 and (CH2CN) z do (van Nes & Vos, 1978).…”

The structures of fluorides. IX. The orthorhombic form of molybdenum hexafluoride

“…Siegel & Northrop (1966) obtained X-ray powder photographs of the low-and high-temperature phases of all the above hexafluorides, and observed a similarity between the X-ray powder patterns of the low-temperature phases and that of UF6. The X-ray patterns, however, were not suitable for detailed structural analysis, and single crystals of the hexafluorides could not be isolated.…”

“…These hexafluorides all undergo a solid-state transformation from a low-temperature phase, which is probably orthorhombic, to a hightemperature phase of body-centred cubic symmetry. The transformation temperatures lie between 263.6 K for MoF6 and 275.2 K for PtF6 (Siegel & Northrop, 1966). Because this phase change occurs at 263.6 K for MoF6, the sample had to be cooled below this temperature to study the orthorhombic phase.…”

The structures of fluorides. XI. Kubic harmonic analysis of the neutron diffraction pattern of the body-centred cubic phase of MoF6 at 266 K

“…Between the melting point (290.6 K) and 263.4 K, MoF6 is body-centred cubic, and below 263-4 K it has an orthorhombic structure of the UF6 type (Hoard & Stroupe, 1958). The hexafluorides of the second and third row transition metals all have a cubic form near room temperature and an orthorhombic form at low temperatures (Siegel & Northrop, 1966 Fluorine-19 magnetic-resonance measurements (Rigny & Virlet, 1969) showed that cubic MoF6 is a plastically crystalline phase with the octahedral MoF6 molecules undergoing rapid rotational and slow translational motions.…”

“…The compounds are highly moisture-sensitive and corrosive and must be handled in quartz or Kel-F, while the crystals sublime and recrystallize owing to their high vapour pressure. Siegel & Northrop (1966) were unable to isolate single crystals for X-ray structure determination in the course of their powder studies.…”