Crown ether-based cryptand/tropylium cation inclusion complexes

Host-guest complexation between crown ether-based cryptand hosts and a carbonium ion, tropylium hexafluorophosphate was studied. 1H NMR, NOESY NMR, and electrospray ionization mass spectrometry were employed to characterize these inclusion complexes. The contrast tests of 1H NMR and association constants indicated that cryptands are much better hosts for tropylium hexafluorophosphate than the corresponding simple crown ethers. C-H⋯O hydrogen bonding, face-to-face π-stacking interactions, and charge-transfer interactions are thought to be the main driving forces for the formation of these host-guest complexes. These multiple non-covalent interactions may jointly contribute to the complex formation and considerably reinforce the complex stability. Moreover, the complexation between dibenzo-24-crown-8-based cryptand 4 and tropylium hexafluorophosphate 7 can be reversibly controlled by adding KPF6 and then DB18C6 in 1:1 acetonitrile/chloroform, providing a new cation-responsive host-guest recognition motif for supramolecular chemistry.