Synthesis and crystal structure of beta-Rb2Te2 and Cs2Te2 as well as the refinement of the structure of Ca2P2 and Sr2As2

Two alkali metal tellurides, which crystallize with a new type of structure, are described: Cs2Te2 type, space group Pbam, Rietveld refinement of powder data (Cs2Te2: a = 11.629(2) Angstrom, b = 6.128(1) Angstrom, 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 described as a lower symmetric, distorted variant of the CsCl type. Furthermore 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. Due to the Na2O2 type of both structures, two crystallographic independent sites exist for the pnicogen atoms. Interestingly, in both compounds two different bond lengths of the two independent dumbells Y-2(4-) are 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).