The layer silicate Cs(2)Sn(IV)Si(6)O(15)

Single crystals of Cs(2)SnSi(6)O(15), dicaesium tin(IV) hexa­silicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO(2) in a closed silica ampoule. The crystal structure of Cs(2)SnSi(6)O(15) is constructed from {Si(6)O(15)}(6–) layers extending parallel to (101), and Cs(I) cations with a coordination number of eleven as well as isolated [SnO(6)] octa­hedra situated between the silicate layers. Each of the nine different SiO(4) tetra­hedra in the silicate layer has a connectedness of Q (3) (three bridging and one terminal O atom), which leads to the formation of five- and eight-membered rings. The same type of silicate layer is found in the crystal structure of the mineral zeravshanite. Comparison with other silicates of the type Cs(2) M (IV)Si(6)O(15) (M (IV) = Ti, Zr, Th, U) revealed a klassengleiche group–subgroup relationship of index 2 between Cs(2)ZrSi(6)O(15) (Z = 6, space group C2/m) and Cs(2)SnSi(6)O(15) (Z = 12, space group I2/c).