C 2Br 4: structure refinements using neutron powder diffraction data in the temperature range 100–300 K

Abstract

The crystal structure of tetrabromoethylene, C 2Br 4, has been refined from neutron powder diffraction data at 300, 260, 210, 160 and 100 K using the Rietveld profile refinement technique. Data were obtained using the high intensity powder diffractometer Polaris at the ISIS pulsed neutron facility. The results of the 300 K refinement agree well with those from single crystal X-ray diffraction, with better estimates for the carbon coordinates. All the low temperature data is also refined succesfully with the same space group, P2 1/c. Significant changes in lattice parameters with temperature lead to anisotropic shifts in the diffraction peaks. An anomaly in the cell parameter “ a” and the slope change in Δ H occur at the same temperature of 210 K and indicate a subtle phase transition.