Abstract Kautsky’s siloxene was prepared in a topochemical reaction from large crystals of CaSi2. The structure model was revised. Siloxene is a subsiliceous acid [Si6]H3(OH)3 and consists of two-dimensional corrugated Si-layers with three Si-Si bonds per silicon and an OH-or H-ligand, respectively. Ordering of adjacent layers is turbostratic. The layer lattice is capable of forming intercalation complexes. On intercalation only the layer distance is changed. The alkoxylated derivatives Si6H3(OCH3)3n and Si6H3(OC2H5)3n are also able to intercalate polar molecules.

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The first compound found to contain planar tetracoordinated silicon is the orthosilicic ester (2). In contrast, the bondilg geometry of the central atom of the analogous orthocarbonic ester deviates only slightly from a tetrahedron. Quantum mechanical studies [e.g. on the model compound (3)] showed that planar tetracoordination is easier for silicon than for carbon. The ability of silicon to engage in sixfold coordination [type(4)] even makes such planar structures easier to achieve than the tertahedral structure.

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