Supramolecular assemblies from uranyl ion complexes of hexa-homo-tri-oxa-calix[3]arenes and protonated [2.2.2]cryptand

The use of [2.2.2]cryptand as a de-protonating agent during the synthesis of the mononuclear, mono-anionic, uranyl ion complexes of p-R-hexa-homo-tri-oxa-calix[3]arenes (R = tert-butyl, phenyl) results in the formation of supramolecular assemblies, which have been characterized by their crystal structures and 1H NMR spectra in solution. In the 1: 1 complex-cryptand assembly, the endo mono-protonated cryptand has its ammonium end embedded in the complex cavity, whereas, in the 2:1 complexes, the endo di-protonated cryptand is encapsulated in a 'sandwich' mode by two complexes with convergent concave surfaces. The latter complexes are the first examples of the use of [2.2.2]cryptand as a 'connector' to build calixarene supramolecular systems. The importance of cation-π interactions in this assembling process is discussed. (authors)