A computational investigation of electronic structure as well as 19F and 29Si chemical shielding tensors in the fluorinated silicon fullerenes SinFn (n≤60)

Density functional theory (DFT) calculations are performed to investigate the electronic features of the structures of fluorinated polysilanes Si_nF_n (n=4, 6, 8, 10, 12, 20, 24, 28, 30, 32, 36, 50, and 60). Among all of these fluorinated polysilanes, Si₂₀F₂₀ has the highest binding energy and, thus, stability. The binding energy then shows a very slow (monotonically) decrease as the size of the fluorinated silicon fullerene n≥20 increases which can be related to an increase in fluorine–fluorine repulsion. Following an irregular pattern, the HOMO–LUMO energy gap strongly depends on the size of the cage. On the other hand, ²⁹Si CS parameters detect equivalent electronic environment for silicon atoms within Si_nH_n polysilanes with n≤20 while ²⁹Si NMR pattern indicates a few separated peaks for Si_nH_n polysilanes with n≥20. Seeking correlation between these peaks and local structures around silicon sites, Si_α, Si_β, Si_γ observed in these models shows that δ_iso(Si_γ)<δ_iso(Si_β) <δ_iso(Si_α). Obtaining similar values (458.8–478.7 ppm) of ¹⁹F calculated chemical shieldings for all the fluorinated polysilanes means the same tendency of the silicon atoms on the surfaces of all cages for contribution to chemical bonding with fluorine atoms.