BN Substituted Non-Classical Fullerenes

The non-classical fullerenes containing other kinds of polygons, such as square or heptagon rings, are within the range of energies spanned by the classical fullerene isomers and may be the competitors of classical fullerenes [1]. Among non-classical fullerenes, we have chosen the C46 and C62 with one square ring and C32 with two square rings to investigate the electronic and magnetic properties of BN substituted non-classical fullerenes, which are fully optimized at the M06-2X/6-311G level. Complete BN substitution of one of the square rings will make a C2-symmetric heterofullerene (C58B2N2, C42B2N2, and C28B2N2). Further BN substitution of the carbon atoms is continued until complete BN substitution of one of the[4] radialene-like structure (C54B4N4, C38B4N4, and C24B4N4). The binding energies of BN substituted non-classical fullerenes are slightly smaller than those obtained for non-classical fullerenes [2]. The IR spectrum in the BN substituted heterofullerenes are similar to those of their parents because of low concentration of B-N impurity, separated into two regions: the stronger absorptions at 1200-1400 cm-1 driven from the stretching of C-B, C-N, B-N, and C-C bonds, while the weaker absorptions at 600-800 cm-1 corresponding to the out-of-plane bending and breathing modes. NICS value in the cage center of C62 is obtained to be -7.05, which is close to that reported for C60. In fact, C62 contains diatropic hexagons and paratropic pentagons with NICS values of -6.6 and +6.9 at the ring centers, respectively. NICS value of C32 is obtained to be -35.3 which is very similar to that reported for the classical C36 fullerene [3]. The compensation between diatropic and paratropic ring currents yields a more negative NICS values in the corresponding BN substituted fullerenes than in C62. The similar ring currents combine to produce non-aromatic character at the center of the BN substituted C46 fullerene. On the other hand, BN-doping affects aromaticity of the whole rings in the C32, leading to decrease of the aromatic character of C28(BN)2 and C24(BN)4 in comparison to their parents.