Is Fullerene C60 Large Enough to Host a Multiply Bonded Dimetal?

Some dimetal fullerenes M 2@C 60 (M = Cr, Mo, W) have been studied with computational quantum chemistry methods. The transition metal diatomic molecules Cr 2, Mo 2, W 2 form exohedral complexes with C 60, while U 2 forms a highly symmetric endohedral compound and it is placed in the center of the C 60 cavity. This highly symmetric structure is an artifact due to the small size of the C 60 cavity, which constrains U 2 at the center. If a larger cavity is used, like C 70 or C 84, U 2 preferentially binds the internal walls of the cavity and the U-U bond no longer exists.