Exploring 11B and 15N NMR parameters of C70-2x (BN) x fullerenes (x=3-25) in connection with local structures and curvature effects: a DFT study

Density functional theory was used to investigate the N-15 and B-11 NMR parameters of heterofullerenes C70-2x (BN) (x) (x = 3, 6, 9, 12, 15, 17, 19, 21, 23, and 25). The geometry structures of all the BN-substituted fullerenes were optimized at the B3LYP/6-31G* level of theory. The B-11 and N-15 nuclear shielding isotropy and anisotropy parameters were then calculated at the same level. The obtained results illustrate that the nuclear shielding isotropy and anisotropy values of the BN-substituted fullerenes C70-2x (BN) (x) divide the nitrogen nuclei into a few groups. A good correlation is seen between the nuclear shielding isotropy and anisotropy values and different local structures around boron and nitrogen atoms. The effects of curvature of the fullerene structure on nuclear shielding parameters of heterofullerenes were also investigated by computing nuclear shielding tensors for curved and relaxed structures of a set of small fragments separated from the heterofullerenes, suggesting high sensitivity of nuclear shielding parameters to the curvature of the fullerene structure.