Abstract. Cs3Bi2Brg; trigonal, P3ml; hexagonal axes; a = 7.972 (2), c = 9.867 (5) A; D,, = 4.65 (2) g cm -3, Z = 1, D c = 4-694 g cm-3; R = 0.058 for 424 reflexions [I > 3o(I)]. Cs and Br are in a cubic close-packed structure, with Bi in ~ of the octahedral holes. The BiBr 6 octahedra share three cis-vertices with three other octahedra forming corrugated layers.
(1)]. In the polycation of this structure the six Bi atoms are located at the corners of an octahedron with the O atoms and OH groups above the centres of the octahedral faces. Each O atom of the OH gxoups has three Bi neighbours arranged pyramidally at longer distances, while the remaining O atoms are linked to three nearly coplanar Bi atoms at shorter distances. Furthermore a NO3 group and the water molecule are bound to two neighbouring Bi atoms.
The isomorphism between ~-BeC12 and ~-BeBr2 was presumed on the basis of X-ray powder diffraction data (Semenenko & Naumova, 1963). The powder pattern of ~-BeBr2 was found to index on a orthorhombic cell with a = 10"32, b = 5.52 and c = 5.54 A. In order to check these results and to obtain accurate crystallographic data, beryllium (II) bromide was synthesized from the elements in a closed glass system at 400°C. Single crystals were grown by means of sublimation. Transparent needle-shaped crystals are extremely sensitive to moisture. They were sealed into Lindemann-glass capillaries.
Crystal geometryCrystal data were obtained using oscillation, Weissenberg and precession photographs.
Comparison with other resultsThe crystal data are in agreement with those found by Semenenko & Naumova (1963). ~-Beryllium (lI) bromide is isomorphous with :~-beryllium (II) chloride for which the crystal data are as follows: a = 9.86, b = 5.36, c = 5.26 A, and space group Ibam (Rundle & Lewis, 1952). The structure consists of chains along the c axis in which BeBr4 tetrahedra are connected by common edges (SIS2 structural type). Unfortunately, the poor quality of the crystals made it impossible to carry out a complete structural analysis.The author is grateful to Professor L. Goli(: for suggesting this work. (1969). 50th ed., pp. B92.
References
Handbook of Chemistry and Physics
Computer ProgramJ. Appl. Cryst. (1975 A diffractometer control program is described which can be used without modification on all Picker Nuclear FACS-I diffractometer equipped with a DF-32 disk. The assembly language program provides a wide variety of preprogrammed data-collection options including an automatic crystal orientation checking algorithm which is described. The program is organized in semi-independent segments to facilitate modification and extension. Several laboratories currently use the program and documentation is available.
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