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

10 alpha.20 alpha-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. H-1 NMR data and solid-state structures of the 1:1 complex of 1 with p-C6H4(COOH)(COO-)+NMe4 and the 2:1 capsule [(1)(2)m-C6H4(COO-)(2)-(+NMe4)(2)] provide structural details in solution and in the solid state.