Inversion Axis Research Articles

The crystal and molecular structure of tetrathiazyl tetra-bis-(trifluoromethyl) nitroxide

The crystal structure of [NSON(CF 3) 2] 4 has been determined by single crystal X-ray diffraction. The crystals are tetragonal, I 4 - , a = b = 16.73(1), c = 4.73(1) Ā, Z = 2. The molecule possesses an eight-membered N 4S 4 ring with a crystallographic inverse tetrad axis at its centre; the nitroxyl radicals are attached to the sulphur atoms. The two independent SN bond lengths are 1.56(1) and 1.62(1) Ā; the geometry of the N 4S 4O 4 moiety is similar to that of N 4S 4F 4.

Space-group Representation in Condensed Models of Inorganic Close-packed Structures

EARLIER I described some condensed models of inorganic close-packed structures1. These were based on standard transparent sheets of film, representing layers of the main types of close packing, in which the occupied holes could be marked out. An approximate three-dimensional representation was obtained by placing these sheets at equal distances in an appropriate supporting rack. It became apparent that the conventional symbols for the elements of symmetry of space groups could also be marked out on these sheets, completing the information contained in the models. The top layers of two of these models, olivine and spinel, are represented in Fig. 1a and b. When the layers are placed in the appropriate supporting rack, screw axes, inversion axes, glide planes, etc., can be easily visualized and related to the actual structure.

The crystal structure of Ce(IO3)4

Zr(lO/sub 3/)/sub 4/ is tetragonal, space group P4/n, with a = 8.38 plus or minus 0.01, and c = 7.49 plus or minus 0.01 A, and has two formula units per unit cell. The complete structure was determined from single crystal data obtained with a Geiger counter. The zirconium atoms are coordinated to eight oxygen atoms at the corners of a nearly perfect antiprism with an average Zr-O distance of 2.206 A. An interesting feature of the structure is that there are voids extending completely through the crystal along the fourfold inversion axis. (auth)