The evolutions of the structure stability, vibrational frequency, frontier orbital, and electronegativity of the unconventional exohedral fullerenes C64X4 (XÂ =Â H, F, Cl, Br, and I): A density functional study

The density functional theory is employed to analyze the evolutions of the structural and electronic properties of the unconventional carbon halogen molecules C64X4 (X = F, Cl, Br, and I). It is found that the evolutions of the bond dissociation energies, the energy gaps, and the maximal frequencies all decrease with the increased atomic number of X, indicating that the stabilities should decrease from C64F4 to C64I4. C64X4 (X = F and Br) could be isolated and synthesized due to the successful isolation of C64Cl4 by Han et al. [X. Han, S.J. Zhou, Y.Z. Tan, X. Wu, F. Gao, Z.J. Liao, R.B. Huang, y.q. Feng, X. Lu, S.Y. Xie, L.S. Zheng, Angew. Chem. Int. Ed. 47 (2008) 5340]. It is revealed from analyzing the frontier orbitals of C64 that the C-C bonds locate on the pentagon-pentagon fusions function as active sites in chemical reactions, facilitating hydrogen atoms or halogen atoms attachment. The electronegativity of C64X4 cluster molecules decrease with the increased atomic number of X, however, the electronegativity of the CX fragment in the molecules is affected by its located site. The molecule electronegativity χ and the chemical hardness η of C64X4 (X = F, Cl, Br, and I) decrease with the increased atomic number of X, while the electrophilicity index ω increases from C64F4 to C64I4. The C3v-C64 is weak aromatic, whereas, the C64X4 (X = F, Cl, Br, I) show nonaromatic character.