Unsubstituted Oxacalix[n]arenes (n=4 and 8): A Conformational Study in Solution and Solid State and Interaction Studies with Aromatic Guests

We present single crystal structures of unsubstituted oxacalix[4]arene and oxacalix[8]arene macrocycles and investigate the weak supramolecular interactions that govern their packing in the solid state. We further show that the unsubstituted oxacalix[4]arene shows weak complexation with two aromatic guest species, benzoic acid and ferrocene, in CDCl₃, whereas the oxacalix[8]arene host does not complex with these guest molecules. We also present NMR titration experiments with non-aromatic acids and DFT calculations that signify the importance of π-π interactions for complexation with benzoic acid. Weak complexation is also observed between electron-rich aromatic guest molecules and the unsubstituted oxacalix[4]arene host.