Conformational Features and Recognition Properties of a Conformationally Blocked Calix[7]arene Derivative

The shaping of a calix[7]arene macrocycle into cone‐like structure 3 , through exhaustive alkylation of doubly bridged calix[7]arene derivative 2 with bulky groups, has been investigated. Conformational details about the structure adopted by calix[7]arene derivative 3 in solution have been obtained by using chemical shift surface maps, as previously reported by our group. Thus, chemical shift contour plots indicated that 3 adopted a cone‐shaped structure in solution analogous to that adopted by the known p ‐ tert ‐butylcalix[7]arene heptacarboxylic acid derivative 4 . Interestingly, the X‐ray structure of derivative 3 showed a high degree of similarity to the theoretical structure, which confirmed the validity of the contour plots method. The preorganized calix[7]arene host 3 showed interesting recognition abilities toward both organic and alkali cations. In fact, an unprecedented endo ‐cavity complexation of linear and branched alkyl ammonium cations with a larger calix[7]arene host was evidenced. A comparable affinity for branched t BuNH 3 + and linear n BuNH 3 + guests was observed.