OCTAHYDRIDOSILASESQUIOXANE DETERMINED BY NEUTRON-DIFFRACTION

The structure of H8Si8O12 has been determined by neutron diffraction at 29 K and compared with X-ray determinations at 9.5 and 100 K. There are only small geometrical differences, but it can be concluded that the deviation from the ideal molecular symmetry, O-h (m (3) over bar m), increases with decreasing temperature and that the large vibration amplitudes for the O atoms observed in the X-ray analyses are also present in the neutron structure. Static disorder of the O atoms is excluded. The molecular deformation is caused by the rigid HSiO3 tetrahedra performing a cooperative torsional movement inducing vibrational deformations of the flexible Si-O-Si angles.