Guest exchange in dimeric capsules of a tetraurea calix[4]arene in the solid state.

A solid powder of hydrogen bonded dimers of a tetraurea calix[4]arene is able to exchange the encapsulated guest in contact with the vapor of a second guest. The molecules of a guest-free powder obtained from a polar solvent cannot rearrange in the solid phase to form new guest-filled capsules under these conditions.