Thermochemical and structural investigations

The phase diagrams of the systems ABr/SmBr₃ were reinvestigated. The findings of Blachnik for the systems withA=Cs, Rb, K were confirmed; however, the dimorphic compound K₃SmBr₆ is stable only above 572 K. The equilibrium temperature, found bye.m.f.-measurements in a solid state galvanic cell for the reaction KBr+K₂SmBr₅=L-K₃SmBr₆, is smaller (522 K). The formation temperature for Rb₃SmBr₆ is 279 K (DTA) and 256 K (e.m.f.) resp. By solution calorimetry was proved that the compounds Cs₂SmBr₅ and KSm₂Br₇ don't exist at 0 K. In the system NaBr/SmBr₃ only one hitherto unknown dimorphic compound Na₃SmBr₃ exists above 473 K. L-Na₃SmBr crystallizes in the hexagonal space groupR¯3, above 519 K H-Na₃SmBr₆ has the monoclinic cryolite-structure. Powder patterns of other compounds not yet investigated — H-/L-A₃ SmBr₆, ASm₂Br₇ (A=Cs, Rb, K) and Cs₂SmBr₅ — were indexed analogously to known structure families. The structure parameters of SmBr₃·6H₂O were determined by single-crystal measurements.This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industry. Michael Alsmann is grateful for a grant of the University Gh Kassel.