Ng7Be2B5+: Binding of Noble Gas Through Both Cationic Beryllium and Anionic Boron Centers

Quantum chemical calculations have been performed to investigate the structure, stability, and bonding in noble gas (Ng) bound Be₂B₅⁺ complexes. The present results show that Be₂B₅⁺, a charge-separated [Be]²⁺[B₅]³⁻[Be]²⁺ cluster, can employ both its cationic Be center and anionic B center to bind Ng atoms. It can bind a total of seven Ng atoms, resulting in the formation of a highly symmetric (Ng^Be)₂Be₂(Ng^B)₅B₅⁺ complex, having D_5h point group. The thermochemical analyses reveal that the Ng-Be bonds are stronger than the Ng-B bonds. (Ng^Be)₂Be₂B₅⁺ (Ng = Ar-Rn) complexes are stable against the dissociation of Ng atoms even at room temperature. But, (Ng^Be)₂Be₂B₅⁺ (Ng = He and Ne) and (Ng^Be)₂Be₂(Ng^B)₅B₅⁺ (Ng = Ar-Rn) complexes are stable only at very low temperatures. Therefore, they can be suitable candidates for low-temperature matrix isolation. A thorough bonding analysis, through charge and energy decomposition methods, discloses that despite the Ng-B interaction being weaker than the Ng-Be interaction, the former bond is more covalent than the latter one. In fact, in the Ng-B bonds, both the orbital and electrostatic interactions are larger in magnitude than the Ng-Be bonds; however, significantly larger Pauli repulsion in the former bonds makes them weaker than the latter bonds. In both Ng-Be and Ng-B bonds, the covalent interaction originates from a strong Ng(p_σ) → Be₂B₅⁺ σ donation, complemented by two weak Ng(p_π) → Be₂B₅⁺ π donations.