The Study Of Aromaticity Of All Possible Heterofullerenes C₁₈B_xN_y And C₂₂B_xN_y(x+y=2) Isomers

Heterofullerenes are fullerenes in which one or more carbon atoms of the cage are substituted by heteroatoms such as boron or nitrogen. Heteroatoms may change the valence-electron count and will change the energy ordering of theÏ€-orbitals, and hence affect aromaticity and stability. The aromaticity of all possible of C₁₈B_xN_y and C₂₂B_xN_y (x+y=2) isomers which are originate from C₂₄ (D6 ) and their molecular ions have been studied by the topological resonance energy (TRE) and the percentage topological resonance energy (%TRE) methods. We found that the substitution of heteroatoms could stabilize fullerenes. Calculation results show that, at the neutral and cationic states all C₁₈B_xN_y and C₂₂B_xN_y isomers are predicted to be antiaromatic, but their polyvalent anions are predicted to be aromatic. Fullerenes are electron-deficient compounds. The results revealed that C₂₀ and C₂₄ have greater tendency to act as electron acceptors than donors. The relationship between aromaticity and the substitution positions of heteroatoms doped have been discussed. By study the aromaticity of C_20-2nX_2n (B, N; n=1,2,3,4) isomers, we found the results are not agreement with the prediction of NICS. At last the reason of the different results caused by the TRE method and NICS value are discussed. We suppose that NICS is not always a reliable criterion of aromaticity.