Insight into the Bonding Mechanism and the Bonding Covalency in Noble Gas-Noble Metal Halides: An NBO/NRT Investigation.

The bonding between noble gas and noble metal halide like hydrogen bonding (H-bonding) motivates us to investigate the bonding mechanism and the bonding covalency in NgMX (Ng = He, Ne, Ar, Kr, Xe, Rn; M = Cu, Ag, Au; X = F, Cl, Br, I) complexes using natural bond orbital (NBO) and natural resonance theory (NRT) methods. In this study, we introduce the new resonance bonding model in H-bonding into NgMX bonding. We provide strong evidence for resonance bonding involving two important resonance structures: Ng: M-X ↔ Ng+-M :X- in each of NgMX complexes, originating in the nNg → σ*MX hyperconjugative interaction. The covalency of the bonding could be understood by the localized nature of Ng-M bonds in these two resonance structures, and the degree of Ng-M covalency can be quantitatively described by calculated NRT bond orders bNgM. Furthermore, we find that the bond order satisfies conservation of bond order, bNgM + bMX = 1, for all of the studied complexes. On the basis of the conservation of bond order and some statistical correlations, we also reveal that the Ng-M bond (except He-Ag and Ne-Ag bonds) can be tuned by changing the auxiliary ligand X. Overall, the present studies provide new insight into the bonding mechanism and the covalency of the bonding in noble gas-noble metal halides, and develop one resonance bonding model.