Characterization of guest molecules sorbed in zeolites of known structure. Part IV — Localization of para-disubstituted benzene molecules at low sorbate-fillings in a zsm-5 material ( [formula omitted])

• Published in: Materials research bulletin 1992, Vol.27 (8), p.953-960
• Main Author: Mentzen, B.F.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-gas interface; Surface physical chemistry
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/0025-5408(92)90195-6

Para-disubstituted benzene molecules (p-xylene, p-chlorotoluene, p-dichlorobenzene and p-dibromobenzene) have been sorbed in an MFI type zeolitic material presenting the H 0.60Al 0.60Si 95.40O 192 framework composition. At room temperature, the evacuated form of this highly siliceous ZSM-5 phase presents the monoclinic symmetry. At lower sorbate-loadings ( n = 2–3 molecules unit-cell ) the four MFI·nsorbate complexes crystallize in the orthorhombic Pnma space group. X-ray powder profile refinements and energy-minimization simulations show that the sorbate molecules are located at the channel-intersections (sites I). The individual molecules interact near sites III ( through the straight-channels) and form dimeric molecular associations. These dimers are oriented parallel to the b-axis direction and are statistically distributed in the crystal structure. At n = 4, the associated molecules form infinite polymeric chains in the 010 direction. The atomic positions of the topology and of the guest molecules have been refined by using linear constraints.