Rotaxane/dibenzo-24-crown-8 macrocycle

The binding of ammonium ion, NH4+, by 18-crown-6 was demonstrated early in the history of macrocycle chemistry. The O-H-N in crowns or N-H-N interaction in azacrowns has been characterized by a variety of techniques, including NMR, calorimetry, and X-ray crystal structure analysis. Recent studies in this area have shown that both quaternary and secondary ammonium salts can form complexes with crowns. In the latter case, a rotaxane molecule was prepared by treatment of a dibenzylammonium salt with dibenzo-24-crown-8 and other macrocycles, including pyrido-24-crown-8. The solid-state structure of the pseudo-rotaxane structure obtained with pyrido-24-crown-8 is shown in the left panel of Figure 23. 

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