Cl@Si20X20 cages: evaluation of encapsulation nature, structural rigidity, and 29Si-NMR patterns using relativistic DFT calculations

The experimental characterization of Cl@Si20 endohedral clusters, featuring different ligands such as [Cl@Si20H20]− (1) [Cl@Si20H12Cl8]− (2), and [Cl@Si20Cl20]− (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 → Si20X20 and 3s-Cl → Si20X20 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, 29Si-NMR parameters are depicted in terms of the chemical shift anisotropy (CSA), leading to a strong variation of the three principal tensor components (δ11, δ22, δ33), unraveling the origin of the experimental 29Si-NMR chemical shift (δiso) differences along the given series. Thus, the Si20 cage is a useful template to further evaluate different environments for encapsulating atomic species.