The crystal and molecular structure of dodecahydridosilasesquioxane, H₁₂Si₁₂O₁₈

The title compound belongs to a family of cage-shaped spherosiloxane molecules which show, as a common and systematic feature, smaller or larger distortions from their respective ideal point-group symmetry. By means of statistical methods in combination with rigid-body analysis, the molecular distortions involved in the lowering of the molecular symmetry of H 12 Si 12 O 18 and (C 6 H 5 ) 12 Si 12 O 18 have been analysed. The magnitudes and types of the deformations may be described in terms of a small number of symmetry displacement coordinates involving displacement of flexibly joined, but otherwise rigid, corner-sharing tetrahedra