Heteroatom Tracing Reveals the 30-Atom Au-Ag Bimetallic Nanocluster as a Dimeric Structure.

Understanding the formation of face-centered cubic (fcc) nanostructures at the atomic level remains a major task. With atomically precise nanoclusters (NCs) as model systems, herein we devised an atom-tracing strategy by heteroatom doping into Au30(SR)18 (SR = S-tC4H9) to label the specific positions in M30(SR)18 NCs (M = Au/Ag), which clearly reveals the dimeric nature of M30. Interestingly, the specific position is also consistent with the Ag-doping site in M21(SR)15. Electronic orbital analysis shows intrinsic orbital localization at the two specific positions in M30, which are decisive to the electronic structure of M30, regardless of Au or Ag occupancy. The fcc dimeric NC, which would not be discovered without Ag tracing, provides a possible explanation for the wide accessibility of nonsuperatomic Au-SR NCs.