Temperature variation of the structural parameters in actinide tetrafluorides
Neutron diffraction has been used to examine the structures of polycrystalline samples of AnF(4) (An = Th, U, and Np). All are isostructural with monoclinic space group C2/c. The structure of UF(4) has been examined in some detail as a function of temperature. The volume of the unit cell has a minimum not at the lowest temperature (15 K) examined, but at around 350 K. ThF(4) also has a larger volume at low rather than room temperature, suggesting that this effect is caused by structural rather than electronic (as ThF(4) has no 5f electrons) interactions. An examination of the coordination around the two independent An sites in UF(4) shows that the fluorine configuration changes appreciably around An2 as a function of temperature. At low temperatures the distorted cubic antiprism structure is considerably more puckered than at higher temperatures. This puckering requires more volume for the molecule, thus causing the volume to expand as the temperature is lowered. The temperature factors and the interatomic distances vary smoothly with temperature and show no unusual behaviour.
Bibliographic Reference: Article: Journal of Chemical Physics, Vol. 101 (1994) No. 11, pp. 9333-9337
Record Number: 199510551 / Last updated on: 1995-04-21
Original language: en
Available languages: en