The layer silicate Cs 2 Sn IV Si 6 O 15 .

Single crystals of Cs 2 SnSi 6 O 15 , dicaesium tin(IV) hexa-silicate, 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 ] octa-hedra situated between the silicate layers. Each of the nine different SiO 4 tetra-hedra 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 C 2/ m ) and Cs 2 SnSi 6 O 15 ( Z = 12, space group I 2/ c ).