Tailoring the Structure of 58-Electron Gold Nanoclusters: Au₁₀₃S₂(S-Nap)₄₁ and Its Implications

Abstract

We report the synthesis and crystal structure determination of a gold nanocluster with 103 gold atoms protected by 2 sulfidos and 41 thiolates (i.e., 2-naphthalenethiolates, S-Nap), denoted as Au₁₀₃S₂(S-Nap)₄₁. The crystallographic analysis reveals that the thiolate ligands on the nanocluster form local tetramers by intracluster interactions of C-H···π and π···π stacking. The herringbone pattern formation via intercluster interactions is also observed, which leads to a linearly connected zigzag pattern in the single crystal. The kernel of the nanocluster is a Marks decahedron of Au₇₉, which is the same as the kernel of the previously reported Au₁₀₂(pMBA)₄₄ (pMBA = -SPh-p-COOH); this is a surprise given the much bulkier naphthalene-based ligand than pMBA, indicating the robustness of the decahedral structure as well as the 58-electron configuration. Despite the same kernel, the surface structure of Au₁₀₃ is quite different from that of Au₁₀₂, indicating the major role of ligands in constructing the surface structure. Other implications from Au₁₀₃ and Au₁₀₂ include (i) both nanoclusters show similar HOMO-LUMO gap energy (i.e., E_g ≈ 0.45 eV), indicating the kernel is decisive for E_g while the surface is less critical; and (ii) significant differences are observed in the excited-state lifetimes by transient absorption spectroscopy analysis, revealing the kernel-to-surface relaxation pathway of electron dynamics. Overall, this work demonstrates the ligand-effected modification of the gold-thiolate interface independent of the kernel structure, which in turn allows one to map out the respective roles of kernel and surface in determining the electronic and optical properties of the 58e nanoclusters.