Abstract:

The molecular geometric and electronic structures of phosphine-stabilized transition-metal cluster [Au@Au₈(PR₃)₈]³⁺(R = Me, OMe, H, F, Cl, CN) were investigated by means of ab initio HF, MP2 and density functional theory(DFT) methods. The bonding energies of Au⁺-Au₈²⁺/Au₈(PR₃)₈²⁺ and [Au@Au₈]³⁺-PR₃ were also analyzed on the basis of calculations. The calculation results show that the D_4d conformations of [Au@Au₈(PR₃)₈]³⁺ are more stable than the D_2h conformations by 5-10 kJ/mol. The local density functio-nal SVWN methods have good performance in reproducing the experimental geometric features. The MP2 calculations underestimate the bond lengths of clusters, while the non-local exchange-correlation functionals and hybrid functionals tend to overestimate the bond lengths. The studies of the electronic structures show that the metal cluster core [Au@Au₈]³⁺ is formed by the d-d electron interaction of Au atoms. The bonding of [Au@Au₈]³⁺-PR₃ complexes can be described as a synergistic combination of σ-donor and π-acceptor interactions between [Au@Au₈]³⁺ and PR₃ ligands. Adding the PR₃ ligands can increase the bonding interaction of Au⁺-Au₈²⁺ and the HOMO-LUMO gap, and reduce the differences of bonding properties between the external Au atoms. Therefore, the stability of the cluster is increased. It is found that the effect of the electron donating or withdrawing ability of PR₃ groups on the geometries of [Au@Au₈(PR₃)₈]³⁺ is small, but that on the bonding energies of [Au@Au₈]³⁺-PR₃ is large. The energy decomposition analysis results show that the orbital interaction energies of the [Au@Au₈]³⁺-PR₃ bonding are very close to each other, so the magnitude of the non-orbital interaction energy plays a crucial role in the stabilization of [Au@Au₈(PR₃)₈]³⁺ complexes.

Key words: Transition-metal cluster, Ab initio, Density functional theory, Electronic structure, Energy decomposition analysis