CRYSTALLOGRAPHIC STUDIES OF 2 POLYMORPHIC FORMS OF THALLOUS FLUORIDE, TIF

The crystal structure of thallous fluoride as described by Ketelaar is in need of revision. Weak reflections have been found in x-ray and electron-diffraction patterns of thallous fluoride which can only be indexed satisfactorily if the space group is changed from Fmmm to Pbcm or Pca 21. Intensity considerations suggest that the latter space group is the correct one; the crystal structure probably involves a distorted cube geometry similar to that found in crystalline thallous methoxide. X-ray measurements of thallous fluoride at different temperatures have revealed a hitherto unknown orthorhombic-tetragonal transition at 82 °C. The relationships between the x-ray diffraction spectra and the structures of the two forms are described. © 1969, Walter de Gruyter. All rights reserved.