A computational NICS and 13C NMR characterization of the polyfluorofullerenes C60Fn (n=18, 20, 24, 36 and 48)

A density functional study has been performed to investigate electronic and magnetic properties of polyfluorofullerenes C60Fn (n = 18, 20, 24, 36, and 48) based on NMR parameters and NICS indices. A few picks appear in the C-13 NMR pattern of each polyfluorofullerene which show the electrostatic environments of carbon nuclei are divided into a few layers related to three local structures around C atoms. Since, hexagons and pentagons in the zone of fluorinated carbon atoms are puckered, the range of isotropic chemical shifts (delta(iso)) related to each group of C atoms are caused by different curvatures at the corresponding sites. According to the calculated spherical excesses Phi(i), chemical shifts are strongly sensitive to the curvature at the corresponding sites in the fullerene cage, so slightly difference in the Phi(i) of carbon atoms leads to change in their delta(iso) values. Moreover, the magnetic properties are examined inside the compounds indicating that independent of the type of polyfluorofullerenes NICS values are strongly negative at the middle of the cage except for the C60F24 and C60F48. The predicted NICS values may be also useful for identification of polyfluorofullerenes through their endohedral He-3 NMR chemical shifts. (C) 2012 Elsevier B.V. All rights reserved.