Supramolecular structures of inclusion complexes of C ₇₀ and cyclic porphyrin dimers

Cyclic nickel and free-base porphyrin dimers (Ni ₂-CPD _Py and H ₄-CPD _Py) include fullerene C ₇₀ both in solution and in the crystals. Based on the ₁₃CNMR spectra in solution, the included C ₇₀ molecule inside the cavity of Ni ₂-CPD _Py shows both end-on and side-on orientations, whereas the C ₇₀ molecule within H ₄-CPD _Py has only a side-on orientation toward the porphyrin rings. X-ray crystallography revealed both "end-on" and "side-on" orientations of C ₇₀ in the crystal structure of the inclusion complex of Ni ₂-CPD _Py and C ₇₀. This is the first example of an X-ray crystallographic determination for an end-on orientation of C ₇₀ cocrystallized with porphyrins. On the other hand, only a side-on orientation of C ₇₀ was observed in the crystal structure of the complex of H ₄-CPD _Py and C ₇₀. Further, a zigzag array of C ₇₀ molecules through van der Waals contacts with each other is formed along the monoclinic b axis in the latter crystal.