Face‐Centered‐Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations

Abstract

Face‐centered‐cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half‐cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half‐cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag6, linear AgS2 (in projection drawing), or tetrahedral AgS3P binding modes, and the sulfur atoms adopt T‐shaped SAg3 and orthogonal SAg4 modes. An additional T‐shaped AgS3 mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ4‐S or μ4‐Ag determines whether growth stops or continues. In particular, a density‐of‐states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS3P motif, regardless of whether the parent NC functions as an electron donor or acceptor.

Rhombicuboctahedral Ag100: Four‐Layered Octahedral Silver Nanocluster Adopting the Russian Nesting Doll Model

“…Several theoretical models have been developed to account for the size‐evolution principles of FCC‐based Ag clusters co‐protected by thiolates and phosphines. As shown in Figure a and b, previously reported FCC‐based Ag clusters mainly exhibit two kinds of evolution models, including the complete cubic evolution model ended with compact cubic blocks and the partial cubic model ended with half‐cubic blocks . Interestingly, Ag 100 does not conform to any of them, instead exhibiting a rhombicuboctahedron structure (Figure c).…”

“…Our understanding of the structures and properties of these Ag NCs has enabled the deduction of their size‐evolution principles and the prediction of very large NCs, which have yet to be reported . So far, the plausibility of these principles is an open question, and their empirical validation is an important area of research.…”

“…However, because of the challenges associated with their synthesis and crystallization, only a few large Ag clusters (Ag 136 , Ag 141 , Ag 146 , Ag 206 , Ag 210‐211 , and Ag 374 ), all of which adopt a multishell model with a decahedral kernel, have been disclosed. The largest FCC‐based Ag cluster reported to date is Ag 67 , although larger FCC‐based Ag clusters incorporating hundreds of Ag atoms have been recently predicted by theoretical methods …”

“…In addition, the outermost {111} facets of Ag 100 (Figure b and c) are end‐capped with AgS 3 P motifs, corroborating our recent theoretical prediction on the blocking activity of {111} facets. This new structural model is informed by a deep understanding of the nucleation and evolution principles for FCC‐based Ag NCs, but is radically different from previous models.…”

Rhombicuboctahedral Ag100: Four‐Layered Octahedral Silver Nanocluster Adopting the Russian Nesting Doll Model

“…evolution principles and the prediction of very large NCs, which have yet to be reported. [6,[25][26][27] So far, the plausibility of these principles is an open question, and their empirical validation is an important area of research. However, because of the challenges associated with their synthesis and crystallization, only a few large Ag clusters (Ag 136 , [28] Ag 141 , [29] Ag 146 , [30] Ag 206 , [31] Ag 210-211 , [32] and Ag 374 [28] ), all of which adopt a multishell model with a decahedral kernel, have been disclosed.…”