Molecular tweezers as synthetic receptors: molecular recognition of neutral and cationic aromatic substrates. A comparison between the supramolecular structures in crystal and in solution

The synthesis of substituted naphthalene- and benzene-spaced tweezer molecules 1b and c and 2e–j is reported. They selectively bind electron-deficient neutral and cationic aromatic substrates. The structural parameters of the substrate–receptor complexes derived from 1H NMR measurements in solution are in good agreement with those obtained from single-crystal structure analyses. The tweezer 2f forms a stable complex with N,N-bis-(3,5-di-tert-butylbenzyl)-4,4′-bipyridinium 14, a substituted viologen dication, that exhibits the structure of a clipped rotaxane with a wheel opened on one side. The benzene-spaced tweezer 2j shows complexation of the cesium cation Cs+ inside the cavity.