Theoretical Studies of the Structures and Stabilities of Dumbell-like Fullerene Dimers: C121

examined by ab initio MO calculations and a hybrid method of Hartree-Fock and DFT. The geometry optimizations gave closed-bond structures (methanofullerene) for all 6,6-bridge and open-bond structures (homofullerene) for all 6,5-bridge structures. Calculations of energies revealed that 2 is the most stable, while 1 is slightly less stable than 2 by ¢(¢Gf°(298.15 K)) ) 2.521 kJ mol-1, and 3 is much less stable than 2 by ¢(¢Gf°(298.15 K)) ) 21.777 kJ mol-1. That is explained by the difference of energy between a methanofullerene and a homofullerene, and the strain energy of the spirojunction at the central bridging carbon atom of C121. The predicted IR and Raman spectra of 1, 2, and 3 indicate that all of 1, 2, and 3 have the same six cage-cage vibrational modes. By comparing the predicted 13C NMR spectra of 1, 2, and 3, and the experimental 13C NMR spectra of C121 isolated by HPLC, we concluded that the structure of the C121 is 2, which is the first C60 dimer that has both a methanofullerene and a homofullerene moiety. 1