Semi-empirical calculations on the BN substituted fullerenes C 60−2 x(BN) x ( x=1–3) — isoelectronic equivalents of C 60

Abstract

The equilibrium structures and relative stabilities of BN substituted fullerenes C 60−2 x (BN) x ( x=1–3) have been studied using AM1 and MNDO semi-empirical methods. The calculation results obtained by both methods indicated that the BN substituted fullerenes are less stable than C 60. The homo–lumo splitting and heat of formation suggests that the isomer of C 58BN in which two neighboring carbon atoms between the six- and six- membered ring are substituted by BN units is the most stable species. The stabilities of C 58BN decrease with increasing the distance between the heteroatoms. For C 56(BN) 2, the calculation results show that N–N and B–B bonds should be avoided and the smallest number of the C–X bonds is preferred for the stable isomer of C 56(BN) 2 and the isomer in which the B–N–B–N bond is formed has the lowest heat of formation, thus the most stable species. The structure of the most stable isomer of C 54(BN) 3 has been proposed based on the calculations on various isomers of C 58BN and C 56(BN) 2, i.e. the most energetic favorable C 54(BN) 3 should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The BN substituted fullerenes C 60−2 x (BN) x have somewhat smaller ionization potentials and bigger affinity potentials compared with C 60, which suggests that it is easier to oxidize and reduce C 60−2 x (BN) x relative to C 60, thus the redox characteristics of C 60 can be enhanced by doping. Based on the optimized geometries, the electronic spectra for these BN doped fullerenes have been calculated using INDO/CIS method