Bond distortion and electronic state of C60 dimer by two electrons uptake

In order to study the electron doping effect on the neutral C60 dimer with the linkage through a [2+2] cycloaddition, structures of the neutral dimer and its dianion have been energetically optimized by the semiempirical Hamiltonian PM-3, The (C60)22− has turned out to have a slightly squashed and equatorially swollen geometry in each C60 compared to the structure of the (C60)2. But both have the same symmetry of D2h. The doped electrons in the dianion will be largely on an equator zone of each C60 ball. The intermolecular center-to-center distance is longer by about 0.03 angstrom in the C60 dimer dianion than in its neutral case.