STRUCTURAL DISTORTIONS IN SI8O12 FRAGMENTS AND D4R UNITS - A COMPARISON BETWEEN SILASESQUIOXANE MOLECULES AND LTA ZEOLITES

The structures of 62 T8O12 units from zeolite A crystal structures and of 16 molecular analogs from R(8)Si(8)O(12) crystal structures have been analyzed for-deformations from m $($) over bar$$ 3m (O-h) symmetry using principal component analysis. Overall, about 95% of the deformations correspond to those expected from a model of rigid tetrahedra joined flexibly across corner-sharing oxygen atoms. The six symmetry deformation coordinates found to be important in the analysis of static distortions are the same as the coordinates associated with the six lowest vibrational frequencies of H8Si8O12.