LOCATION OF PERDEUTERATED BENZENE SORBED AT LOW PORE-FILLING IN A H.MFI MATERIAL - A NEUTRON POWDER DIFFRACTION STUDY

A synthetic H.MFI material presenting the H1.30Al1.30Si94.70O192 frame work composition and containing 2.2C6D6 molecules sorbed at low pore-f illing has been studied at room temperature by neutron powder diffract ion (ILL, Grenoble, D2B diffractometer, lambda = 2.4 angstrom). The ex perimental profile was analysed by combining profile-fitting structure refinements (Rietveld method with geometric restraints), interpretati on of difference-Fourier maps and energy-minimization calculations usi ng the atom-atom potential method (Buckingham model). At low pore-fill ing (<4 molecules/unit-cell), the deuterobenzene species are localized and disordered at the channel-intersections. This statistical orienta tional disorder can be modelled by considering two limiting orientatio ns of the benzene molecules.