Binding of neutral molecules by p-nitrophenylureido substituted calix[4]arenes

Although originally designed for anion recognition, bis(N′-p-nitrophenylureido)calix[4]arenes immobilised in the 1,3-alternate conformation can act as receptors for small neutral molecules, such as sulfoxides and ketones. Their binding ability was studied both in solution and in the solid state using the combination of UV/vis, NMR, and X-ray crystallography.