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 ] 2Γ , where the two independent Rb + cations (site symmetry 3) are located in the voids.
Related literature
For studies of phase transitions of langbeinites, see: Ukeda et al. (1995);Dilanian et al. (1999). Double sulfates of the langbeinite-type were summarized by Gattow & Zemann (1957). For single-crystal structure analyses of selected langbeinites, see: Zemann & Zemann (1957); Guelylah et al. (1996); Guelylah & Madariaga (2003). Differences between the langbeinite and the Nasicon structure are discussed by Sizova et al. (1981) and DroΓ & Glaum (2004). Parameters for the bond valence sum (BVS) analysis were taken from Brown & Altermatt (1985).
Experimental
Crystal data
Rb 2 Ca 2 (SO 4 ) 3 M r = 539.28 Cubic, P2 1 3 a = 10.553 (3) A V = 1175.2 (6) A Λ3 Z = 4 Mo K radiation = 9.79 mm Γ1 T = 293 K 0.22 Γ 0.13 Γ 0.05 mm Data collection Stoe-Siemens AED2 four-circle diffractometer Absorption correction: multi-scan (MULABS in PLATON; Spek, 2003) T min = 0.231, T max = 0.644 1236 measured reflections 1080 independent reflections 658 reflections with I > 3(I) R int = 0.08 2 standard reflections frequency: 30 min intensity decay: 0.7% Refinement R[F 2 > 2(F 2 )] = 0.065 wR(F 2 ) = 0.128 S = 1.12 1080 reflections 59 parameters Γ max = 0.93 e A ΛΓ3 Γ min = Γ1.00 e A ΛΓ3 Absolute structure: Flack (1983), 558 Friedel pairs Flack parameter: 0.00 (4) 2
(vi) Γz ΓΎ 2; x ΓΎ 1 2 ; Γy ΓΎ 3 2 ; (vii) Γz ΓΎ 1; x Γ 1 2 ; Γy ΓΎ 1 2 ; (viii) x; y; z Γ 1.