pH‐Controlled Molecular Switches and the Substrate‐Directed Self‐Assembly of Molecular Capsules with a Calix[4]pyrrole Derivative

Abstract

10alpha,20alpha-Bis(4-nitrophenyl)calix[4]pyrrole (1) forms 1:1 complexes with anions of selected aromatic hydroxy acids in which the host orientation within the guest is controlled by a change in the pH value. Some bis-anionic guests, including those obtained from 4-hydroxybenzoic acid, 1,4- and 1,3-benzenedicarboxylic acids, induce the self-assembly of molecular capsules involving two molecules of the receptor. (1)H NMR data and solid-state structures of the 1:1 complex of 1 with p-C(6)H(4)(COOH)(COO(-))(+)NMe(4) and the 2:1 capsule [(1)(2)m-C(6)H(4)(COO(-))(2)((+)NMe(4))(2)] provide structural details in solution and in the solid state.