Host−Guest Complexes with <i>p</i>-Sulfonatocalix[4,5]arenes Charged Crown Ethers and Lanthanides: Factors Affecting Molecular Capsule Formation

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-sulfonatocalix[4]arene, 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-sulfonatocalix[5]arene was elusive under the conditions studied. Rather, an “alternative host−guest bilayer” structure formed in the presence of europium(III) ions.