New Perspectives on the Electronic and Geometric Structure of Au70S20(PPh3)12 Cluster: Superatomic-Network Core Protected by Novel Au12(µ3-S)10 Staple Motifs

摘要

In order to increase the understanding of the recently synthesized Au70S20(PPh3)12 cluster, we used the divide and protect concept and superatom network model (SAN) to study the electronic and geometric of the cluster. According to the experimental coordinates of the cluster, the study of Au70S20(PPh3)12 cluster was carried out using density functional theory calculations. Based on the superatom complex (SAC) model, the number of the valence electrons of the cluster is 30. It is not the number of valence electrons satisfied for a magic cluster. According to the concept of divide and protect, Au70S20(PPh3)12 cluster can be viewed as Au-core protected by various staple motifs. On the basis of SAN model, the Au-core is composed of a union of 2e-superatoms, and 2e-superatoms can be Au3, Au4, Au5, or Au6. Au₇₀S₂₀(PPh₃)₁₂ cluster should contain fifteen 2e-superatoms on the basis of SAN model. On analyzing the chemical bonding features of Au₇₀S₂₀(PPh₃)₁₂, we showed that the electronic structure of it has a network of fifteen 2e-superatoms, abbreviated as 15 × 2e SAN. On the basis of the divide and protect concept, Au₇₀S₂₀(PPh₃)₁₂ cluster can be viewed as Au₄₆¹⁶⁺[Au₁₂(µ₃-S)₁₀⁸⁻]₂[PPh₃]₁₂. The Au₄₆¹⁶⁺ core is composed of one Au₂₂¹²⁺ innermost core and ten surrounding 2e-Au₄ superatoms. The Au₂₂¹²⁺ innermost core can either be viewed as a network of five 2e-Au₆ superatoms, or be considered as a 10e-superatomic molecule. This new segmentation method can properly explain the structure and stability of Au₇₀S₂₀(PPh₃)₁₂ cluster. A novel extended staple motif [Au₁₂(µ₃-S)₁₀]⁸⁻ was discovered, which is a half-cage with ten µ₃-S units and six teeth. The six teeth staple motif enriches the family of staple motifs in ligand-protected Au clusters. Au₇₀S₂₀(PPh₃)₁₂ cluster derives its stability from SAN model and aurophilic interactions. Inspired by the half-cage motif, we design three core-in-cage clusters with cage staple motifs, Cu₆@Au₁₂(μ₃-S)₈, Ag₆@Au₁₂(μ₃-S)₈ and Au₆@Au₁₂(μ₃-S)₈, which exhibit high thermostability and may be synthesized in future.