AN EXAFS STUDY OF THE METALLOFULLERENE YC82 - IS THE YTTRIUM INSIDE THE CAGE

A sample, determined by time-of-flight mass spectroscopy (TOFMS) to consist of YC82 as the major metal-fullerene complex, was analyzed by X-ray absorption spectroscopy. The Y is found to have 7 +/- 1 near-neighbor C atoms at 2.35 +/- 0.02 angstrom and an Y neighbor at 4.05 +/- 0.05 angstrom. The unequivocal observation of an Y-Y interaction is unexpected, since the mass spectral data show no indication of Y2Cn as a major component of the sample. We believe that the combined TOFMS and extended X-ray absorption fine structure (EXAFS) results are not consistent with models that place the metal ion inside the fullerene cage. Instead, we propose that our data can be explained with a dimer of the form C82Y-X-YC82, where -X-is a bridging carbon or oxygen species. The short Y-C near-neighbor distance indicates a strong, bonding interaction between the metal ion and the fullerene cage.