CRYSTAL AND MOLECULAR-STRUCTURE OF COMPOUNDS CONTAINING A HYPERVALENTO-SI(C3)-O FRAGMENT - PARAMETRIZATION IN THE DESCRIPTION OF THE COORDINATION ENVIRONMENT OF THE SILICON ATOM

We have carried out an X-ray structural investigation of four pentacoo rdinated silicon compounds with a hypervalent O-Si(C3)-O fragment. In their molecules, the axial Si-O bond lengths range from 1.711 to 2.785 angstrom. Analysis of the geometry of such fragments containing other atoms in axial positions shows that the main parameter determining th e state of the hypervalent fragment is deviation of the Si atom from t he plane of equatorial substituents. Some consequences of this study f or structural modeling of nucleophilic substitution reactions are disc ussed.