Unraveling the Atomic Structures of the Au₆₈(SR)₃₄ Nanoparticles

The atomic structure prediction of thiolate-protected gold nanoparticle (RS-AuNP) Au₆₈(SH)₃₄ is performed based on the “divide and protect” concept and experimental studies on 14 kDa RS-AuNPs. Four low-lying energy isomers, <b>Iso1</b>–<b>Iso4</b>, were identified by the density-functional theory. Our results indicate the most stable structure <b>Iso2</b> adopts the <i>C</i>_2<i>v</i> Au₅₀ core with Marks-decahedral (m-Dh) Au₁₈ inner core. The calculated HOMO–LUMO gap is 0.74 eV, which is very close to that of Au₆₇(SR)₃₅^2–. Further analysis suggests the 14 kDa RS-AuNPs might be not only the turn point between the fused core structure and the compact core structure but also the turn point between the one-shell inner core structure and the multishell inner core structure. The threshold number of Au atoms in bulk-like RS-AuNPs is evaluated as ∼263 based on the linear fitting of the HOMO–LUMO gaps of various RS-AuNPs including Au₆₈(SR)₃₄. The research on the medium-sized Au₆₈(SR)₃₄ establishes a bridge between smaller and larger RS-AuNPs, which is beneficial for us to better understand the structures of the RS-AuNPs