The gas-phase structure of octaphenyloctasilsesquioxane Si _8O_(12)Ph_8 and the crystal structures of Si _8O_(12)(p-tolyl)_8 and Si_8O _(12)(p-ClCH_2C_6H_4)_8

摘要

The equilibrium molecular structure of octaphenyloctasilsesquioxane Si _8O_(12)Ph_8 in the gas phase has been determined by electron diffraction. It was found to have D_4 point-group symmetry, with Si-O bond lengths of 1.634(15)-1.645(19) ?, and a narrow range [147.5(45)-149.8(24)°] of Si-O-Si angles. The structures of Si _8O_(12)(p-tolyl)_8 and Si_8O _(12)(p-ClCH_2C_6H_4)_8 have been determined by X-ray diffraction and are found to have Si_8O _(12) cages significantly distorted from the symmetry found for Si _8O_(12)Ph_8 in the gas phase. Thus, Si-O-Si angles range between 144.2(2)-151.64(16)°for Si_8O_(12)(p-tolyl) _8, and between 138.8(2)-164.2(2)°for Si_8O _(12)(p-ClCH_2C_6H_4)_8. These three structures show how much a Si_8O_(12) cage may be distorted away from an ideal structure, free from intermolecular forces, by packing forces in a crystalline lattice.