Incorporation of the smallest diprotonated diaza-functionalized crown ethers into host-guest assemblies with p-sulfonatocalix[4 or 5]arenes gives insight into the dominant factors in the formation of ``molecular capsule'' or ``alternative host-guest bilayer'' structures in the solid state, in the presence of aquated lanthanide(III) cations. For p-sulfonatocalixarene, molecular capsule formation is dependent on guest size, protonation of the diaza-crown ether, and the pH of the reaction medium. In contrast, formation of (di)aza-crown ether-based molecular capsules with p-sulfonatocalixarene was elusive under the conditions studied. Rather, an ``alternative host-guest bilayer'' structure formed in the presence of europium(III) ions.
Dalgarno, S. J., Atwood, J. L., & Raston, C. L. (2006). Host-guest complexes with p-sulfonatocalix[4,5]arenes charged crown ethers and lanthanides: factors affecting molecular capsule formation. Crystal Growth and Design, 6(1), 174-180. https://doi.org/10.1021/cg050261q