OCTAHYDRIDOSILASESQUIOXANE DETERMINED BY NEUTRON-DIFFRACTION

The structure of H8Si8O12 has been determined by neutron diffraction a t 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 t he deviation from the ideal molecular symmetry, O-h (m (3) over bar m) , increases with decreasing temperature and that the large vibration a mplitudes for the O atoms observed in the X-ray analyses are also pres ent in the neutron structure. Static disorder of the O atoms is exclud ed. The molecular deformation is caused by the rigid HSiO3 tetrahedra performing a cooperative torsional movement inducing vibrational defor mations of the flexible Si-O-Si angles.