Motif-to-Core Nucleation in a Decahedral Evolution Pattern

The atomic precision of ultrasmall metal nanoclusters has opened the door to elucidating the structural evolution principles of metal nanomaterials at the molecular level. Here, we report a novel set of super-atomic Ag clusters, including [Ag₁₉(TBBT)₁₆(DPPP)₄]⁺ (Ag₁₉), [Ag₂₂(DMAT)₈(DPPM)₄Cl₈]²⁺ (Ag₂₂), Ag₂₆(SPh^3,5-CF₃)₁₅(DPPF)₄Cl₅ (Ag₂₆), and [Ag₃₀(DMAT)₁₂(DPPP)₄Cl₈]²⁺ (Ag₃₀). The core structures of these clusters correspond to one decahedral Ag₇, perpendicular bi-decahedrons, three-dimensional penta-decahedrons, and hexa-decahedrons, respectively. The Ag atoms in AgS₂ blocks show a strong correlation with the decahedral cores: the five equatorial Ag atoms in the decahedral Ag₇ core of Ag₁₉ all adopt the AgS₂ coordination, while the Ag atoms in AgS₂ blocks of Ag₂₂, Ag₂₆, and Ag₃₀ unexceptionally constitute additional decahedral structures with the core Ag atoms. Specifically, two and four core Ag atoms of Ag₂₆ and Ag₃₀ clusters occupy positions that highly resemble that of Ag (in AgS₂ motifs) of Ag₂₂. The strong structural correlation demonstrates the motif-to-core evolution of the surface Ag (on AgS₂) to build extra-decahedral blocks. Density functional theory calculations indicate that the 2e, 4e, 6e, and 8e clusters (from Ag₁₉ to Ag₃₀) adopt 1S², 1S²1P², 1S²1P⁴, and 1S²1P⁶ electron configurations, all of which feature excellent super-atomic characters.