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.