Fullerene nanostructures: how the oblong shape of C forms a cocrystal with an enormous asymmetric unit and related cocrystals.

Cocrystallization of NiII(OEP) (where OEP is the dianion of octaethylporphyrin) with C70 in p-xylene produces black plates of 12NiII(OEP)·12C70·18p-xylene (1). Single crystal X-ray diffraction at 90 K reveals that the crystal contains 42 individual, well-ordered molecules in the asymmetric unit with distinctive interactions between each NiII(OEP)/C70 pair and each pair of neighboring C70 molecules. Warming the crystal to 186 K produces a phase change so that only four NiII(OEP)/C70 sites and six p-xylene molecules are present. Under the same conditions CuII(OEP) cocrystallizes with C70 to form CuII(OEP)·C70·1.5p-xylene (2) with a much simpler structure consisting of one molecule of the porphyrin and the fullerene along with 1.5 molecules of p-xylene in the asymmetric unit. Crystallization of C70 from toluene in the presence of NiII(etioporphyrin-I) produces the black solvate 6C70·6toluene (3). It seems that C70 has a tendency to crystallize so that several orientations of the oblong molecule are present in the solid.