The colourless compounds Li3OBr and Li7O2Br3 have been prepared and characterized by X-ray diffraction techniques. Li3OBr crystallizes in a cubic primitive lattice (Pm3m) with a = 405.6(1) pm (Z = 1). The structure is related to the anti-perovskite type. Li7O2Br3 crystallizes in a tetragonal bodycentered lattice (I4/mmm) with a = 403.5(1) pm, c = 2161(1) pm (Z = 2) and is isotypic to Sr3Ti2O7.

The colourless compounds KLiSe and KNaSe have been prepared and characterized by powder measurements. KLiSe crystallizes in a tetragonal lattice with a — 451.7(1), c = 7274 1(2) pm, Z. = 2 (P4/nmm). KNaSe crystallizes in the orthorhombic space group Pnma with a = 806.3(2), b = 481.7(1) and c = 865.1(2) pm, Z = 4.

Rubidium Lithium Sulphide, Crystal Structure The colourless com pound RbLiS has been prepared as described earlier (H . Sabrowsky, A . Thim m . and P. Vogt-M ertens, Z. Naturforsch. 40b, 1759 (1985)) and its crystal structure determ ined by X-ray diffraction. V ery hygroscopic RbLiS crystallizes in the tetragonal space group P4/nmm (Z = 2) with the cell parameters a -4.424(3) Ä , c = 7.255(2) Ä . The structure was solved from 1635 counter reflections (155 symmetry independent reflections) by Patterson and Fourier m ethods (R = 0.031; w R = 0.031). T he structure is characterized by layers o f 2 [LiS4/4]-tetrahedrons separated by double-layers of R b + to form a PbFCl-type geom etry.

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The colourless compound Na3O(CN) has been prepared. The characterization by X-ray powder methods leads to a cubic primitive lattice (P m 3 m) with a = 456(2) pm (Z = 1). The structure is related to the anti-perovskite type.