Abstract:
M06L/6-311++G(d,p)//M06L/6-31G(d,p) level density functional theory studies show that the endohedral
reaction of C60 with X (X = F, Cl, Br, OH, NH2, NO2, CN, and ClO) is exothermic by 37.8–65.2 kcal mol 1.
The exothermic character of the reaction is drastically reduced in polar and nonpolar solvents due to the lack
of direct solvation influence on the encapsulated anion. In all X @C60, the occupied frontier molecular orbitals
(FMOs) are located on X while the energy levels of FMOs centered on C60 are very similar to those of the
C60
radical anion. Molecular electrostatic potential (MESP) analysis of X @C60 revealed that the negative
character of the MESP minimum (Vmin) on the carbon cage increases by B72 fold compared to C60, which is
very similar to the enhancement in the negative MESP observed on the C60
radical anion. The MESP data
and quantum theory of atoms in molecules (QTAIM) analysis of charge, electron delocalization index, and
Laplacian of bond critical point (bcp) support significant electron sharing from the anion to the carbon atoms
of the fullerene cage, which makes the cage behave like a very large anion in a closed shell configuration.
The data are also supportive of a multicenter charge-shift type of bonding interaction between the anion
and the carbon cage. The anionic nature of the fullerene cage has been verified in the cases of larger
systems such as Cl @C70, Cl @C84, and Cl @C90. The binding of a counter cation K+ with X @C60 is
found to be highly exothermic (B72 kcal mol 1) and very similar to the binding of K+ with the C60
radical
anion (72.9 kcal mol 1), which suggests that C60 in X @C60 behaves as a closed shell anion.
