A systematic investigation on the molecular behaviors of substituted fullerenes C 34X 2 (X=N, B)

Abstract

A systematic investigation on the molecular behaviors of all the possible isomers of C 34B 2 and C 34N 2 formed from the initial C 36 fullerene with C 6 v and C 6 h symmetries have been performed using the semi-empirical AM1 and MNDO methods. The equilibrium geometrical structures, heats of formation, HOMO–LUMO gap energies, heats of atomization, ionization potentials (IP) and affinity potentials (AP), conjugate effect and deformation energies of C 34X 2 (X=N, B) have been studied. The calculation results show that the heterofullerenes are less stable than C 36, and the C 34N 2 should be more stable than the boron analog C 34B 2. Both empirical methods in this work indicate that the most stable isomer of C 34X 2 (X=N, B) corresponds to 1,4-substitution in the cyclohexatriene unit which locating at the equatorial belt of the C 36 cage. Generally speaking, the C 34X 2 (X=N, B) isomers with the doped atoms near the equatorial belt are more stable that the rest. The heterofullerenes C 34X 2 have bigger IP and smaller AP compared with C 36, thus the redox activity of C 36 can be reduced by doping. The results of π-orbital axis vector analysis show that replacements of carbon atoms with either nitrogen or boron can notably release the strains in local part of the cage. Both C 34N 2 and C 34B 2 are expected to have significantly different chemical and physical properties from those of the fullerenes.