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 ...