Metal Ion Effects on Fullerene/Porphyrin Cocrystallization

This investigation presents a systematic examination of the late transition metal octaethylporphyrins MII(OEP) with M = Co, Ni, Cu, and Zn as cocrystallization agents for C60. In each case, the fullerene was dissolved in benzene and then layered over an equimolar dichloromethane solution of the porphyrin. A striking new columnar structural type for these systems is found for CoII(OEP) and ZnII(OEP) with stoichiometric ratios 6:5 for porphyrin/fullerene. In these cocrystals, one fullerene is surrounded by two porphyrins, one is adjacent to only one porphyrin, while one makes no contact with a porphyrin; yet, all three fullerenes are ordered at 90 K. A more typical, also new, 1:1 structure with CuII(OEP) and C60 shows back-to-back porphyrins with all eight ethyl groups embracing the fullerene. In these three structures only dichloromethane is found as the solvate. The NiII(OEP) structure is related to the known structure of NiII(OEP)·C60·2C6H6 but has incorporated ca. 5% dichloromethane. In these NiII(OEP)/C60 cocrystals, four of the ethyl groups embrace the fullerene, while the other four are displaced to the opposite side of the porphyrin plane where they do not make contact with a fullerene. The porphyrin core conformations of the different metal derivatives also differ, and their possible impact on cocrystal formation is discussed.