SYNTHESIS AND CRYSTAL-STRUCTURE OF BETA-R B2TE2 AND CS2TE2 AS WELL ASTHE REFINEMENT OF THE STRUCTURE OF CA2P2 AND SR2AS2

Two alkali metal tellurides, which crystallize with a new type of stru cture, are described: Cs2Te2 type, space group Pbam, Rietveld refineme nt of powder data (Cs2Te2: a = 11.629(2) Angstrom, b = 6.128(1) Angstr om, c = 4.960(1) Angstrom; beta-Rb2Te2: a = 11.151(1) Angstrom, b = 5. 854(1) Angstrom, c = 4.821(1) Angstrom). This structure type may be de scribed as a lower symmetric, distorted variant of the CsCl type. Furt hermore we report the single crystal refinements of the structures of two alkaline earth pnicogenides M'Y-2(2)(Ca2P2,Sr2As2) in order to get exact information about the bond lengths of the Y-2(4-)-dumbbells. Du e to the Na2O2 type of both structures, two crystallographic independe nt sites exist for the pnicogen atoms. Interestingly, in both compound s two different bond lengths of the two independent dumbells Y-2(4-) a re found (Ca2P2: P-P: 2.268(8) Angstrom and 2.320(4) Angstrom; Sr2As2: As-As: 2.521(9) Angstrom and 2.574(5) Angstrom).