THE SILICALITE(MFI) P-NITROANILINE SYSTEM - I - LOCATION OF THE SORBED MOLECULES AT MEDIUM AND HIGH PORE-FILLINGS - A STUDY BY X-RAY-POWDERDIFFRACTION, SI-29 MAS NMR AND ENERGY MINIMIZATION CALCULATIONS/

Structural investigation of the silicalite(MFI)/np-nitroaniline system by X-ray powder diffraction, establishes the existence of two single phased host/guest complexes corresponding to n=4 and 8 at medium and h igh pore-fillings respectively. Predictive studies by molecular mechan ics simulations indicate that the pNAN molecules are located at the ch annel-intersections (for n=4) or in the elliptic channel-sections of t he MFI topology (for n=8). Si-29 solid-state mas NMR measurements show that the actual MFI framework symmetry of the silicalite.4pNAN comple x is acentric Pn2(1)a. Interpretation of the XRD pattern corresponding to the saturated silicalite.8pNAN complex by Rietveld type structure refinements shows that two independent pNAN molecules are located on s ites II (zig-zag channel sections) and sites III (straight channel sec tions). The van der Waals type interactions between the sorbed molecul es take place at the channel-intersections (sites I). These sites are not occupied by extra-framework species. This is in agreement with the commensurability criterion already observed in several MFI/sorbate sy stems.