DFT Studies on Non-IPR C_(68) and Endohedral Fullerene Sc_3N@C_(68)

The structures and spectra of 20 possible isomers of C78(CH2)3 have been studied by using AM1,INDO/CIS and DFT methods. The results show that the most stable isomer is 1,2,3,4,5,6-C78(CH2)3 (A) with annulene structures,where three -CH2 groups are added to the 6/6 bonds located at the same hexagon passed by the shortest axis of C78 (C2v). Compared with that of C78 (C2v),the first absorption in the electronic spectrum of C78(CH2)3 (A) is blue-shifted because of its wider LUMO-HOMO energy gap. While the IR frequencies of the C–C bonds on the carbon cage are red-shifted owing to the formation of annulene structures and the extension of the conjugated system. The chemical shifts of the carbon atoms in 13C NMR spectra are moved upfield upon the addition.

DFT Studies on Non-IPR C68 and Endohedral Fullerene Sc3N@C68

Density functional theory (DFT) calculations on two isomers of C68 with the minimal number of fused pentagon pairs, its anions and Sc3N as well as Sc3N@C68 (6140) metallofullerene were carried out at the B3LYP/6-31G* level. The optimized configurations and electrostatic potential distributions have been obtained. The calculated results show that the electrostatic potentials of C68 (6140) inside the sphere have three minima in the middle of the double bonds at fusion of two hexagonal rings. In contrast, potential minimum Vmin(r) of C68 (6275) inside the sphere occurs at the center of the sphere. Concerning the two isomers of C68, the largest regions with the most negative MEP outside the sphere are both localized in the neighborhood of pentagon-pentagon vertex fusions. They constitute the most probable active sites in chemical reactions.Our results present a reasonable explanation for the bonding between scandium atoms and fullerene cage.