Theoretical studies on the substitution patterns in heterofullerenes C70-xNx and C70-xBx (x=2-10)

A systematic investigation on possible structures of heterofullerenes C70-x Nx and C70-xBx (x = 2-10) has been performed, and their electronic properti es have been calculated employing semiempirical AM1, PM3, MNDO, and ab init io, methods. It was found that the heterofullerenes C70-nXn are less stable than their all-carbon analogues and the N-doped fullerenes are thermodynam ically more stable than their B-doped analogues. The stabilities decrease w ith increasing number of heteroatoms. The structures whose carbon atoms are substituted in the para pattern across the equatorial hexagons correspond to the most stable isomers Of C70-xNx and C70-xBx, and the redox characteri stics can be fine-tuned by doping. Our previously proposed correlation betw een the isomerism of the fullerene adducts C60Xn and that of the heterofull erenes C60-nNn or C60-nBn holds true for C-70 adducts and doped C-70 system s, which allows us to deduce the isomerism of the doped C-70 fullerenes on the basis of the relatively well studied regioselectivity of [70]fullerene adducts. The aromaticity of the most stable structures of heterofullerenes decreases with increasing number of the heteroatoms in the system, and N-do ped structures are slightly more aromatic than their B-doped analogues.