Structural studies of polycrystalline octavinyloctasilsesquioxane – (C2H3)8Si8O12

Abstract The structure of polycrystalline materials may differ significantly from that determined from monocrystalline studies. The combination of measurement and calculation techniques is one of the most effective ways to determine structural differences. The use of x-ray powder diffraction (XRD) supported by Monte Carlo calculations as well as complementing these studies with Fourier-transform infrared spectroscopy (FTIR) supported by ab initio calculations helped to determine the structure of octavinyloctasilsequioxane as a powder specimen. The results show a rhombohedral distortion of the cubic-shaped molecule along the ternary axis of the unit cell. Monte Carlo calculations support the model wherein vinyl groups at the Si atom sites along the C 3 axis could be located at one of the three equivalent positions, with the possibility of rapid reorientation. XRD measurements, as a function of temperature, show structural transition from a hexagonal (rhombohedral) to a low symmetry (probably triclinic) orientation, but through an intermediate monoclinic space group.