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Zusammenfassung:
A systematic investigation on possible structures of heterofullerenes C70-xNx and C70-xBx (x = 2−10) has been performed, and their electronic properties have been calculated employing semiempirical AM1, PM3, MNDO, and ab initio methods. It was found that the heterofullerenes C70-nXn are less stable than their all-carbon analogues and the N-doped fullerenes are thermodynamically more stable than their B-doped analogues. The stabilities decrease with 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 characteristics can be fine-tuned by doping. Our previously proposed correlation between the isomerism of the fullerene adducts CXn and that of the heterofullerenes C60-nNn or C60-nBn holds true for C70 adducts and doped C70 systems, which allows us to deduce the isomerism of the doped C70 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-doped structures are slightly more aromatic than their B-doped analogues.
