Germanosilicate Cs2In2[(Si2.1Ge0.9)2O15](OH)2 · H2O with a New Corrugated Tetrahedral Layer: Topological Symmetry-Based Prediction of Anionic Radicals

Crystals of a new germanosilicate Cs2In2[(Ge0.4Si0.6)2(Ge0.3Si0.7)2(Ge0.2Si0.8)2O15](OH)2 · H2O were prepared by the hydrothermal synthesis; sp. gr. Pnma, a = 13.3159(3) A, b = 9.2615(2) A, c = 14.9222(4) A. The structure was found to contain a new layered tetrahedral radical. The cores composed of InO6 octahedra are decorated on both sides by (Si,Ge)O4 tetrahedra, which is typical of many layered minerals, for example, of palygorskite and sepiolite. The layers were found to be corrugated due to the presence of large Cs cations in the structure. The principles of formation of anionic radicals are considered. The diversity of anionic radicals is attributed to various symmetrical-topological types of chains and different types of connectedness and arrangement in layers and frameworks in terms of symmetry. Two new hypothetical layers containing four-, six-, and eight-membered rings are predicted based on a deerite chain identified in the layer of the new compound.