Au_130-x Ag_x Nanoclusters with Non-Metallicity: A Drum of Silver-Rich Sites Enclosed in a Marks-Decahedral Cage of Gold-Rich Sites

The synthesis and structure of atomically precise Au_130-x Ag_x (average x=98) alloy nanoclusters protected by 55 ligands of 4-tert-butylbenzenethiolate are reported. This large alloy structure has a decahedral M₅₄ (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag-rich sites is found, which is enclosed by a Marks decahedral cage of Au-rich sites. The surface is exclusively Ag-SR; X-ray absorption fine structure analysis supports the absence of Au-S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non-plasmon nature. The non-metallicity of the Au_130-x Ag_x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic-level insights into the Au-Ag bonds in bimetallic nanoclusters.