Planar Tetracoordinate Silicon

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.