Alkalimetallrheniumsulfide und -selenide mit [Re6X8]-Baueinheiten

Alkali Metal Rhenium Sulphides and Selenides Containing Re₆X₈] Clusters The sulphides Rb₄Re₆S₁₃ and Rb₂K₂Re₆S₁₃ were synthesized by the reaction of alkali metal carbonates with rhenium in a stream of H₂S at 800°C. The preparation of the selenides Cs₄Re₆Se₁₃,-Rb₄Re₆Se₁₂, and K₄Re₆Se₁₂ succeeded when a hydrogen atmosphere charged with selenium was used. By combining both reaction methods we obtained mixed crystals of the composition Cs₄Re₆S_9.45Se_3.55. Structural investigations on single crystals revealed atomic arrangements in which Re₆X₈] clusters are linked threedimensionally by X and X₂ bridges. In the A₄Re₆X₁₂-type a {Re₆X₈]X_4/2(X₂)_2/2}^4? framework is found whereas the corresponding notation for the A₄Re₆X₁₂-type is {Re₆X₈]X_2/2(X₂)_4/2}^4?. The dependence of the respective type of framework on the size of the alkali metal ions will be discussed. The diamagnetic behaviour, which was measured in the temperature range between 3.8 and 300 K corresponds with the existence of nearly regular Re₆-octahedra with a 24-electron configuration.