Noble Gas—Silicon Cations: Theoretical Insights into the Nature of the Bond

The structure, stability, and bonding situation of some exemplary noble gas-silicon cations were investigated at the MP2/aVTZ level of theory. The explored species include the mono-coordinated NgSiX(3)(+) (Ng = He-Rn; X = H, F, Cl) and NgSiF(2)(2+) (Ng = He-Rn), the di-coordinated Ar(2)SiX(3)(+) (X = H, F, Cl), and the “inserted” FNgSiF(2)(+) (Ng = Kr, Xe, Rn). The bonding analysis was accomplished by the method that we recently proposed to assay the bonding situation of noblegas compounds. The Ng-Si bonds are generally tight and feature a partial contribution of covalency. In the NgSiX(3)(+), the degree of the Ng-Si interaction mirrors the trends of two factors, namely the polarizability of Ng that increases when going from Ng = He to Ng = Rn, and the Lewis acidity of SiX(3)(+) that decreases in the order SiF(3)(+) > SiH(3)(+) > SiCl(3)(+). For the HeSiX(3)(+), it was also possible to catch peculiar effects referable to the small size of He. When going from the NgSiF(3)(+) to the NgSiF(2)(2+), the increased charge on Si promotes an appreciable increase inthe Ng-Si interaction, which becomes truly covalent for the heaviest Ng. The strength of the bond also increases when going from the NgSiF(3)(+) to the “inserted” FNgSiF(2)(+), likely due to the cooperative effect of the adjacent F atom. On the other hand, the ligation of a second Ar atom to ArSiX(3)(+) (X = H, F, Cl), as to form Ar(2)(SiX(3)(+)), produces a weakening of the bond. Our obtained data were compared with previous findings already available in the literature.