Cl@Si 20 X 20 cages: evaluation of encapsulation nature, structural rigidity, and 29 Si-NMR patterns using relativistic DFT calculations.

The experimental characterization of Cl@Si 20 endohedral clusters, featuring different ligands such as [Cl@Si 20 H 20 ] - (1) [Cl@Si 20 H 12 Cl 8 ] - (2), and [Cl@Si 20 Cl 20 ] - (3), provides insight into the variable encapsulation environment for chloride anions. The favorable formation of such species enables the evaluation of the encapsulation nature and the role of the inner anion in the rigidity of the overall cluster. Our results show a sizable interaction which increases as -66.7, -100.8, and -130.3 kcal mol -1 from 1 to 3, respectively, featuring electrostatic character. The orbital interaction involves 3p-Cl → Si 20 X 20 and 3s-Cl → Si 20 X 20 charge transfer channels and a slight contribution from London dispersion-type interactions. These results show that the inner bonding environment can be modified by the choice of exobonded ligands. Moreover, 29 Si-NMR parameters are depicted in terms of the chemical shift anisotropy (CSA), leading to a strong variation of the three principal tensor components ( δ 11 , δ 22 , δ 33 ), unraveling the origin of the experimental 29 Si-NMR chemical shift ( δ iso ) differences along the given series. Thus, the Si 20 cage is a useful template to further evaluate different environments for encapsulating atomic species.