The new alkali cyclotrisilicate Cs₈[Si₆O₁₆]

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[Si₆O₁₆] was solved and refined from single crystal X-ray diffraction data: new structure type, P anti 1, Z = 2, a = 9.3544(3) Aa, b = 11.1152(4) Aa, c = 13.5035(5) Aa, 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 [SiO₄] tetrahedra which form three interconnected rings: two rings consisting of three tetrahedra share edges with the opposite sides of a square of four [SiO₄] tetrahedra. With respect to the plane of the four-membered rings the triangles strike a trans-type arrangement. [Si₆O₁₆]^8- is the first example of the third possible structural arrangement in the class of unbranched dimeric cyclotrisilicate anions. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)