The crystal structure and anisotropic temperature vibration of ammonium cyanide

NH 4 CN crystallizes in a tetragonal structure. Cell dimensions: a = 4.16,c = 7.61 Å. space group: D 10 4h ‐ P4 /mcm. The atomic positions are given on p. 40, on which also a figure is seen showing the structure. This bears much resemblance to the CsCl‐structure of the other NH 4 ‐halides. (The cell is doubled in the direction of the c‐axis by the orientation of the CN‐groups. The CN‐groups oscillate in the planes (110) and (1¯10), respectively. This follows from the fact, that at room temperature intensity calculation of reflections with large third index, as compared with neighbouring reflections with small third index, give much too high results, the addition of an anisotropic heat factor yielding agreement between observed and calculated intensities both at room and low temperatures. The fact that the c‐axis increases considerably with temperature points to the same conclusion.