TIME RESOLVED CRYSTALLOGRAPHY OF GUEST/HOST-COMPOUNDS: MOLECULAR RECOGNITION AND PHASE TRANSITIONS IN SODALITES M[SiO₂]₆. J. Felsche, P. Behrens^*, C. Braunbarth, W. Bührer^***, G. Engelhardt^**, P. Fischer^***, G. Van De Goor*. ^*Dept.Chemistry, University of Konstanz, D-78434 Konstanz, Germany; ^**Ludwig-Maximilians-University, D-80333 München, Germany^{; ***}University of Stuttgart, D-70550 Stuttgart, Germany^, ETH-Zürich & Paul Scherrer Inst., CH-5232-Villigen, Switzerland

There is a limited number of five molecules M known so far which direct the sodalite structure via molecular recognition in hydrothermal and H₂O-free syntheses conditions¹. The cubic host structure of the SiO₂-SOD-phases, which are well characterized by X-ray and neutron diffraction data, show unlike all the other clathrasil-types no 5-membered but instead 4- and 6-membered rings on the microporous tetrahedral framework structure. We have chosen this group of model clathrasils in order to focus our attention to the crystallography of the organic molecules M of low symmetry which, trapped in the 4⁶6⁸-SOD-cages and isolated by the 3D-periodic SiO₂-matrix, cause a typical pattern of multi-stage phase transitions into the host structure as shown by DSC-microcalorimetry and synchrotron powder diffraction data. We report here on the experimental results of three spectroscopic methods IR-spectrocopy, quasi-elastic neutron scattering and MAS-NMR-spectroscopy of the nuclei ¹H, ¹³C, ²⁹Si which reveal the guest/guest- and as well the guest/host-interactions through different time windows of frequences 10¹² to 10¹⁵ cps, 10⁸ to 10¹² cps and 10⁴ to 10⁸ cps, respectively. Starting from the frozen in disorder statistics at 10K up to the critical temperatures of about 800K, where thermal decomposition and/or oxidation of the guest molecules occurs, structural phase transitions at temperatures T_st and as well glass points T_g demonstrate critical characters in the van der Waals guest/host-interactions of molecular recognition.

¹C.Braunbarth et. al.; Zeolites 1996 16 207-217.