pH-Controlled molecular switches and substrate-directed self-assembly of molecular capsule with a calix[4]pyrrole derivative

10alpha,20 alpha -Bis(4-nitrophenyl)-calix[4]pyrrole (1) forms 1:1 complexes with anions of selected aromatic hydroxyl acids in which the host orientation within the guest is controlled by a change in the pH value. Some bisanionic 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-C6H4(COOH)(COO-)+NMe4 and the 2:1 capsule [(1)2m-C6H4 (COO-)2 (+NMe4)2] provide structural details in solution and in the solid state.