Evolution of 4e-Superatom Networks in Au₄(AuL)_1–12 Nanoclusters (L = Cl, SH, PH₂, SCH₃)

Ligand-protected gold (Au–L) nanoclusters have been widely studied due to their interesting optical, electronic, and charging properties. The superatom concept (SAC) and superatom-network (SAN) model are the two known tools, which are used to explain the electronic stability of Au–L nanoclusters. Ever since the crystal determination of the Au₁₀₂(SR)₄₄ cluster, there have been many subsequently crystallized Au–L nanoclusters. However, the size evolution of the superatom network in Au–L nanoclusters is still little known because of a lack of experimental data. To give a direct and overall view of size evolution of the superatom networks in Au–L clusters, the 4e Au₄(AuL)_1–12 (L = Cl, SH, PH₂, SCH₃) system is taken as a test case. The global minimum geometries have been explored using a first principle global minimization technique, namely, genetic algorithm from density functional theory geometry optimization (GA-DFT). The superatom networks in these structures are composed by two of the Au₃, Au₄, Au₅, or Au₆ 2e-superatoms protected by staple motifs. The SAN model is used to explain the chemical bonding patterns, which are verified by chemical bonding analysis based on the adaptive natural density partitioning (AdNDP) method. The clusters which have triangular Au₃ and tetrahedral Au₄ superatoms are also analyzed by the recently proposed grand unified model. The aromatic analysis on the basis of nucleus-independent chemical shifts (NICS) method indicates that the superatoms in SANs of the clusters are highly aromatic. This work gives a clear size-evolution of the 4e-superatom networks for Au–L clusters with 1 to 12 ligands, which discovers the growth mechanism of Au–L clusters with different ligands