Interatomic Distances from X-Ray Power Photographs. The Crystal Structure of Mercuric Tellurate

The Fourier series is discussed as a method for obtaining directly the arrangement of atoms within a crystal, and difficulties in this method are pointed out. A recently developed treatment of x-ray powder photographs giving interatomic distances is tested on various substances and found to be satisfactory when applied to compounds c011taining relatively few heavy atoms- in reasonably simple arrangement. Crystalline diphyenyliodonium iodide is shown to have an ionic bond between the iodine atoms. The sulfur bond angle 1ti orpiment is measured, and great similarity is found to exist between the structures of orpiment and realgar. The arsenic-sulfur distance in sodium sulfantimonate is found to be smaller than that predicted by the table of radii or Pauling and Huggins. A short discussion is given of the difficulties encountered in applying this method. On the basis of an incomplete investigation into the crystal structure or mercuric tellurate, Hg3TeO6, the TeO6 group is shown to exist as a unit here as in telluric acid, with a shape that is nearly regularly octahedral. The unit cell size is found, and a determination of the space group is made.