caesium; crystal structure; group-subgroup relation; silicates; tin
en
Abstract:
Single crystals of Cs₂SnSi₆O₁₅, dicaesium tin(IV) hexa-silicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO₂ in a closed silica ampoule. The crystal structure of Cs₂SnSi₆O₁₅ is constructed from {Si₆O₁₅}6- layers extending parallel to (101), and CsI cations with a coordination number of eleven as well as isolated [SnO₆] octa-hedra situated between the silicate layers. Each of the nine different SiO4 tetra-hedra in the silicate layer has a connectedness of Q3 (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 Cs₂MIVSi₆O₁₅ (M IV = Ti, Zr, Th, U) revealed a klassengleiche group-subgroup relationship of index 2 between Cs₂ZrSi₆O₁₅ (Z = 6, space group C2/m) and Cs₂SnSi₆O₁₅ (Z = 12, space group I2/c).
