Dimeric molecular capsules under redox control.

A new tetraferrocenylurea calix[4]arene was prepared in order to investigate its dimerization properties. 1H NMR spectroscopic data clearly established that this calixarene forms stable dimeric molecular capsules in chloroform solution. The dimeric capsules are stabilized by the formation of multiple hydrogen bonds between the urea functional groups on the calixarene upper rims. In the dimer, eight ferrocene groups are held in proximity to the "seam" of hydrogen bonds. Upon oxidation of the ferrocene residues, electrochemical, PGSE NMR, and IR spectroscopic data revealed that the hydrogen bonds are broken, leading to the dissociation of the dimeric molecular capsule.