Ba(3)[Sn(OH)(6)][SeO(4)](2)·3H(2)O, a hydrated 1:2 double salt of barium hexa­hydroxidostannate(IV) and barium selenate(VI)

Single crystals of tribarium hexa­hydroxidostannate(IV) bis­[selenate(VI)] trihydrate, Ba(3)H(12)O(17)Se(2)Sn or Ba(3)[Sn(OH)(6)][SeO(4)](2)·3H(2)O, prepared from solid BaSnO(3) and aqueous Na(2)[SeO(4)] solutions have hexa­gonal (P6(3)) symmetry. The structure consists of four different primary building units: a hexa­hydroxidostannate(IV) ion, two different selenate(VI) ions, all three of point group symmetry C (3), and a mono-capped {BaO(9)}-square anti­prism of point group symmetry C (1). The secondary building units result from three of the barium coordination polyhedra linked together via common edges. While one of the two tetra­hedral voids formed from these trimeric units is filled by one bidentate, chelating μ(2)-selenate ion, the other one remains unoccupied as the corresponding second selenate ion only acts as a monodentate, μ(1)-ligand. SBUs are completed by hexa­hydroxidostannate(IV) ions sharing adjacent edges on the uncapped faces of the three, mono-capped square anti­prisms. These SBUs are arranged into layers via common edges on the uncapped, square faces of the {BaO(9)} coordination polyhedra in a way that the hexa­hydroxidostannate(IV) ions act as linkage between two neighboring layers.