Structure and guest dynamics for calix[4]arene derivative inclusion compounds

Structure and guest dynamics of the p-t-butylcalix[4]arene derivative including aromatic molecule (benzene and pyridine) were studied by means of single-crystal XRD and solid state NMR. The single-crystal XRD studies on these compounds at 130 K show a guest molecule in the host cavity. Pyridine inclusion compound, however, contains another pyridine molecule outside the cavity. Both guests in the cavity show quite similar orientations except their dynamics. Variable temperature 2H NMR spectra on the benzene compound suggest an in-plane rotation of the benzene about C6 axis even at 80 K. On the other hand, the pyridine in the cavity remains static at least up to 240 K pointing its nitrogen atom outside the cavity, although outside one undergoes rapid in-plane oscillation. The guest dynamics are restricted by the two aromatic rings of the host except benzene C6 reorientation.