Rare gas bond property of Rg–Be2O2 and Rg–Be2O2–Rg (Rg = He, Ne, Ar, Kr and Xe) as a comparison with Rg–BeO

We have investigated the bond properties of Rg–Be2O2 and Rg–Be2O2–Rg and compared to that of Rg–BeO by using high level quantum chemical calculation. It is found that more than half of the binding energies for all Rg–Be2O2 complexes come from the contribution of the electron correlation. However, in the series of Rg–BeO, the influences of the electron correlation to the binding energies are much smaller than those of Rg–Be2O2 series. These results indicate that the rare gas bonds are more van der Waals nature in Rg–Be2O2 cases. The strong van der Waals nature of Rg–Be2O2 series result in the monotonous increment of the bonding energy from He–Be2O2 to Xe–Be2O2 according to the size dependent orbital distortion of the rare gas atoms. On the other hand, a significant amount of back-donation from 2pπ on O to 2pπ on Be is observed in He–BeO. The existence of this mechanism would facilitate the charge transfer from He to BeO and stabilize the He–BeO bond.