Fullerene nanostructures: how the oblong shape of C70 forms a cocrystal with an enormous asymmetric unit and related cocrystals

Abstract

Cocrystallization of Ni^II(OEP) (where OEP is the dianion of octaethylporphyrin) with C₇₀ in p-xylene produces black plates of 12Ni^II(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 Ni^II(OEP)/C₇₀ pair and each pair of neighboring C₇₀ molecules. Warming the crystal to 186 K produces a phase change so that only four Ni^II(OEP)/C₇₀ sites and six p-xylene molecules are present. Under the same conditions Cu^II(OEP) cocrystallizes with C₇₀ to form Cu^II(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 Ni^II(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.