Modulation of the Double-Helical Cores: A New Strategy for Structural Predictions of Thiolate-Protected Gold Nanoclusters

A fundamental understanding of the structural growth of thiolate-protected gold nanoclusters not only benefits experimental synthesis but also will advance the methodology for structural predictions and for rational design of highly stable nanoclusters. Herein, we report numerous new structures (11 total) of thiolate-protected gold nanoclusters predicted from theoretical modulation of the double-helical cores of experimentally determined nanoclusters. Among these newly predicted structures, Au₃₂(SR)₂₂, Au₄₀(SR)₂₆, and Au₄₈(SR)₃₀ are obtained by adding a defective layer containing 4 gold atoms on a structural sequence of experimentally crystallized nanoclusters, namely, Au₂₈(SR)₂₀, Au₃₆(SR)₂₄, and Au₄₄(SR)₂₈. The generic growth pattern underlying this sequence of nanoclusters can be viewed as adding the highly stable tetrahedral Au₄ unit on the double-helical cores. Likewise, the other eight newly predicted structures, including two groups of isomeric structures corresponding to the sequence of experimentally determined Au₂₈(SR)₂₀, Au₃₆(SR)₂₄, Au₄₄(SR)₂₈, and Au₅₂(SR)₃₂ nanoclusters, are successfully predicted. Density functional theory calculations show that these 11 newly predicted nanoclusters exhibit large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and all-positive harmonic vibrational frequencies, suggesting their high chemical stabilities. Additional analyses on the structures and properties suggest that these newly predicted nanoclusters are very likely to be synthesized in the laboratory. Confirmation by experiments would validate the new strategy for structural prediction of thiolate-protected gold nanoclusters by taking advantage of a large structure database of crystallized ligand-protected gold nanoclusters with a variety of gold cores.