Chemical reactivity of lithium-doped fullerenes

The addition of free radicals and the 1,3 dipolar cycloaddition onto pristine and lithium-doped C60 were studied by means of the PerdewBurkeErnzerhof (PBE) and M06-2X density functionals. In all cases, lithium increased the reactivity even though for the 1,3 dipolar cycloaddition onto C60 the change observed with respect to bare C60 was minimal. Both functionals employed gave similar encapsulation energies for Li@C60 namely, 33.1 and 38.2?kcal/mol at the PBE/6-31G* and M06-2X/6-31G*, respectively. However, the increased reactivity because of lithium doping determined at the PBE level is smaller as compared with that computed with the M06-2X functional, whereas that determined at the second-order M circle divide llerPlesset (MP2) level is the largest one. For example, using the M06-2X functional the binding energy of fluorine to Li@C60 is 28.5?kcal/mol larger than that determined for C60, whereas at the PBE/6-31G* level it is predicted to be increased by 24.7?kcal/mol. The results clearly suggest that Li@C60 is a much better free radical scavenger than C60. Finally, the complex hindered rotations of lithium inside C60 are expected to be strongly inhibited because lithium doping increases the well depth between the cage center and the equilibrium position near the addition site of the lithium atom. Copyright (c) 2011 John Wiley & Sons, Ltd.