The new alkali cyclotrisilicate Cs₈[Si₆O ₁₆]

Transparent single crystals of Cs₈[Si₆O₁₆] have been obtained by a high-temperature reaction at 900 °C in an arc-welded niobium crucible. The structure of Cs₈[Si ₆O₁₆] was solved and refined from single crystal X-ray diffraction data: new structure type, P1, Z = 2, a = 9.3544(3) Å, b = 11.1152(4) Å, c = 13.5035(5) Å, α = 101.311(3)°, β = 100.958(3)°, γ = 114.121(3)°, R₁ = 0.032. The structure of Cs₈[Si₆O₁₆] contains isolated dimeric cyclotrisilicate anions [Si₆O₁₆]^8- that are separated by cesium atoms.The anion consists of six vertex-sharing [SiO ₄] tetrahedra which form three interconnected rings: two rings consisting of three tetrahedra share edges with the opposite sides of a square of four [SiO₄] thetrahedra. With respect to the plane of the four-membered rings the triangles strike a trans-type arrangement. [Si ₆O₁₆]^8- is the first example of the third possible structural arrangement in the class of unbranched dimeric cyclotrisilicate anions.