Key indicators: single-crystal X-ray study; T = 293 K; mean (S-O) = 0.010 Å; R factor = 0.065; wR factor = 0.128; data-to-parameter ratio = 18.3.Single crystals of dirubidium dicalcium tris[sulfate(VI)], Rb 2 Ca 2 (SO 4 ) 3 , were obtained from solid-state reactions of Rb 2 SO 4 and CaSO 4 . The title compound crystallizes in the cubic langbeinite-type structure. It features two crystallographically independent CaO 6 octahedra (each with site symmetry 3), which are linked by sharing corners with SO 4 tetrahedra to establish a framework with composition [Ca 2 (SO 4 ) 3 ] 2À , where the two independent Rb + cations (site symmetry 3) are located in the voids.

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We consider the spaces F µ of polynomial µ-densities on the line as sl(2)-modules and then we compute the cohomological spaces H 1 diff (sl (2), Dλ ,µ ), where µ ∈ R,λ = (λ 1 , . . . , λ n ) ∈ R n and Dλ ,µ is the space of n-ary differential operators from F λ1 ⊗· · ·⊗F λn to F µ .Mathematics Subject Classification (2010). 17B56