3253 ment sulfate. Les plans cationiques sont relativement peu d6form6s par rapport 5. l'hydroxyde mais il y a n6cessairement rupture dans l'enchainement des octa~dres dans une couche de type brucitique. La pr6sence des ions SO4 provoque un 6cartement des octa6dres repr6sent6 en pointill6s sur la Fig. 3 The crystal structure of y-Cd2(OH)2804 has been determined by a single-crystal X-ray study. The compound crystallizes in a unit cell of symmetry P21/n, with the following parameters: a= 6-900 (1), b= 7-567 (2), c= 9-964 (2) A, fl= 97.17 (2)°; Z=4. Data were collected on a Nonius CAD-4 automatic diffractometer. The structure was solved by the heavy-atom method and refined to R and R" values of 0"036 and 0-043 for 1201 independent reflexions. The structure consists of distorted octahedra sharing edges, which form two similar layers parallel to (110) and (1]0), and joined by SO4 groups.

The crystal and molecular structure of (N,N-difluoroamino)-2,4-dinitrobenzene has been determined from three-dimensional X-ray data collected by counter methods. The compound crystallizes in the monoclinic space group P21/c with eight molecules in the unit cell. Cell dimensions are a = 11.974 (4), b= 11-040 (4), c= 14.435 (6) ~, fl= 119.76 (5) , V= 1657 &3. Refinement for 1658 reflexions with FZo> 2a(Fo) z converged to conventional and weighted R values of 0.058 and 0.042. The nitrogen atom of the amine group has a pseudo-tetrahedral coordination and evidence for a nonbonded interaction between this atom and an oxygen atom of the ortho nitro group is given. The details of the geometry of the molecule are compared with those previously determined. The molecular packing is also discussed.