Isostructural species are found in the solid state for the supramolecular 1:2 complexes of a calix[6]arene molecule and either C60 or C70 (see the structure of the [(calix[6]arene)(C60)2] complex on the right). The calixarene assumes a double-cone conformation, and the overall structure is a result of the complementarity of the building blocks with respect to size and form—in other words, the shallow calixarene cavity and the fullerene surface have similar curvatures.