New insights into the stability and structural evolution of some gold nanoclusters

Revealing the stability and structural patterns is important for precisely synthesizing or assembling ligand protected nanoclusters, and even their applications as functional nanomaterials. Investigations on structural evolutional patterns and structural stability are very challenging, because structures change with the nanocluster size and the structural stability depends on both the electron structures of cores and ligand type. Herein, we propose a hybrid superatom network (hSAN) model to understand the stability of some gold nanoclusters with different kinds of ligands. In this model, 4c-2e superatom Au₄ can form conjugated superatom networks by vertex sharing, and ligands further connect the conjugated superatom networks together to form a bigger complex network, i.e. a hSAN. The stability of the clusters, including [Au₂₄(C[triple bond, length as m-dash]CPh)₁₄(PPh₃)₄]²⁺, Au₂₈(S-c-C₆H₁₁)₂₀, Au₃₆(SCH₂Ph-tBu)₈Cl₂₀, Au₄₀(O-MBT)₂₄ and Au₅₂(TBBT)₃₂ can be explained uniformly by the hSAN model. Beyond that, a new heuristic structural pattern named the Au₁₃ topological rule is proposed. In the light of this heuristic rule, every Au₇ bi-tetrahedral kernel is included in an Au₁₃ structure with quasi-O_h symmetry, i.e. as long as the Au₇ bi-tetrahedral kernel is formed, it will be surrounded by six Au atoms to form an Au₁₃ structure topologically. According to this understanding, a new nanocluster [Au₄₄(C[triple bond, length as m-dash]CH₃)₂₆(PCH₃)₄]²⁺ and a new nanowire with the structural evolutional formula [Au_(20n+4)(C[triple bond, length as m-dash]CH₃)_(12n+2)(PCH₃)₄]²⁺ (n = 1, 2, 3, 4, …) are predicted. Both the understanding of the stability and the structure rule are free from the type of ligand, and will be useful for the structural predictions and determinations of ligand protected gold nanoclusters.