Calix[6]arenes often serve as molecular host in supramolecular chemistry, however, they show a conformation flexibility due to the inversion of the aromatic rings. It is important to control the structure flexibility of calix[6]arenes. In this work, a C3v-symmetrical molecular receptor calix[6]TPA was synthesized and characterized via 1H NMR, 13C NMR, ESI-MS, and X-ray structural analysis. Molecular recognitions of calix[6]TPA for small organic ammoniums were investigated with 1H NMR, and the inclusions of the straight chain ammoniums were reversiblly controlled by the acidity of the solution. The results indicate that the introduction of a tripodal N4-crypto cap is beneficial to rigidify the structure in a cone conformation, the hydrophobic cavity is an efficient receptor for organic guests, and the reversible recognition of straight chain ammoniums can be potentially applied in separation of organic amines.
