Crystallographic Determination of the Positions of the Monovalent H, Li, Na, K, Rb, and Tl Cations in Fully Dehydrated MFI Type Zeolites

The locations and populations of several monovalent cations in H-, Li-, Na-, K-, Rb-, and Tl[I]-exchanged Zeolite Socony-Mobil #5 (ZSM-5) zeolitic materials (Mobil Five (MFI) framework structure) were determined crystallographically by interpreting X-ray (synchrotron source radiation) or neutron (for H-MFI samples only) powder diffraction profiles, using the Rietveld-type structure refinement method. The present work is a continuation of general research on zeolitic host−guest complexes concerning Cs-exchanged (Mentzen, B. F.; Bergeret, G.; Emerich, H.; Weber, H.-P. J. Phys. Chem. B 2006, 110, 97; Mentzen, B. F.; Bergeret, G.; Emerich, H.; Weber, H.-P. J. Phys. Chem. B 2006, 110, 13741; and Mentzen, B. F.; Rakhmatkariev, G. U.; Bergeret, G.; Weber, H.-P. J. Phys. Chem. C 2007, 111, 3820−) and Cu-exchanged MFI phases (Mentzen, B. F.; Bergeret, G. J. Phys. Chem. C 2007, 111, 12512−). As in Cs-exchanged phases, the fully dehydrated K-, Rb-, and Tl(I)-MFI samples present straight channel 10-ring sections (SC), which are markedly elliptical (major axis in the O1···O7 direction). In a Na 6.7 H 0.2 -MFI phase, the orientation of the major axis of the elliptical channel deformation corresponds to the O5···O11 direction. For H- and Li-exchanged samples, the 10-ring SC sections are almost circular. Except for a deuterobenzene loaded H 0.72 (C 6 D 6 ) 3.6 -MFI sample (Si/Al = 132), the framework symmetry is orthorhombic Pnma . The heavier cations (Na, K, Rb, and Tl[I]) are directly located by interpreting difference Fourier maps, whereas the positions of the lighter H (charge compensating protons) and Li species are determined by refining the populations (negative populations are rejected) corresponding to the theoretically calculated H (O−H = 1.0 Å) and Li (O−Li = 2.0 Å) locations (26 possible sites for each cation in the Pnma space group).