Toward Total Synthesis of Thiolate-Protected Metal Nanoclusters

Abstract

CONSPECTUS: Total synthesis, where desired organic-and/or biomolecules could be produced from simple precursors at atomic precision and with known step-by-step reactions, has prompted centuries-lasting bloom of organic chemistry since its conceptualization in 1828 (Woḧler synthesis of urea). Such expressive science is also highly desirable in nanoscience, since it represents a decisive step toward atom-by-atom customization of nanomaterials for basic and applied research. Although total synthesis chemistry is less established in nanoscience, recent years have witnessed seminal advances and increasing research efforts devoted into this field. In this Account, we discuss recent progress on introducing and developing total synthesis routes and mechanisms for atomically precise metal nanoclusters (NCs). Due to their molecular-like formula and properties (e.g., HOMO−LUMO transition, strong luminescence and stereochemical activity), atomically precise metal NCs could be regarded as "molecular metals", holding potential applications in various practical sectors such as biomedicine, energy, catalysis, and many others. More importantly, the molecular-like properties of metal NCs are sensitively dictated by their size and composition, suggesting total synthesis of them as an indispensable basis for reliably realizing their practical applications. Atomically precise thiolate-protected Au, Ag and their alloy NCs are employed as model NCs to exemplify design strategies and governing principles in total synthesis of inorganic nanoparticles. This Account starts with a brief summary of total synthesis methodologies of atomically precise metal NCs. Following the methodological summary is a detailed discussion on the mechanisms governing these synthetic strategies, which is the main focus of this Account. Based on unprecedented precision (at atomic resolution) and ease (ensured by size-dependent properties) of tracking clusters' size/structure changes, mechanisms driving growth (e.g., reduction growth and seeded growth) and functionalization (e.g., alloying reaction and ligand exchange) of metal NCs have been explored at molecular level. With def initive step-by-step reaction routes, two-electron (2 e − ) reduction (driving the growth reactions) and surface motif exchange (SME, prompting alloying and ligand exchange reactions) are discussed in depth and details. In addition to those sub-and/or individual-cluster level understandings, the self-assembly chemistry delivering high orderliness and enhanced materials performance in NC assemblies/supercrystals is also deciphered. This Account is then concluded with our perspectives toward potential development of cluster chemistry. Advances in total synthesis chemistry of metal NCs could not only serve as guidelines for future synthetic practice of NCs, but also provide molecular-level clues for many pending fundamental puzzles in nanochemistry, including nucleation growth, alloying chemistry, surface engineering and evolution of metamaterials.

Systematically Tuning the Electronic Structure of Gold Nanoclusters through Ligand Derivatization

“…Atomically-precise gold nanoparticles are valued for their potential as photocatalysts,p hotovoltaics,c hemical sensors, non-linear optical media, etc.,a nd our fundamental understanding of the chemical/physical properties relevant to such applications has undergone ar enaissance over the past decade due to advances in synthetic protocols selective for their isolation and crystallization. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Crystallographic characterization of ligand-protected gold nanoparticles has revealed high-symmetry core structures protected by the socalled "staple motif" for thiols or, in the case of phosphines, halides,orh ydrocarbons,direct metal core-ligand binding. [14] Such detailed geometric characterization has been pursued due to its potential to establish structure/function relationships in the synthesis of "designer" nanomaterials.…”

The Synthesis of Chiral Ag4Pd2(SR)8 by Nonreplaced Galvanic Reaction

“…During the past decade, atomically precise doped nanoclusters (NCs, ultrasmall nanoparticles with size less than ≈2 nm) have gained considerable attention from nanoscientists because of the synergistic or even new properties (e.g., catalytic and optical properties) of doped NCs compared to their homometallic counterparts. [1][2][3][4][5][6][7][8][9][10] A general synthesis method is the synchrosynthesis (i.e., the mixed metal precursors are concurrently reduced by reducing agent like NaBH 4 ), such as the preparation of Au 24 Pd(SR) 18 , [11,12] Au 24 Pt(SR) 18 , [12][13][14] Au 25−x Ag x (SR) 18 , [15] Au 38−x Ag x (SR) 18 , [16] Au 36 Pd 2 (SR) 18 , [17] Au 36 Pt 2 (SR) 24 , [17] Ag 24 Pd(SR) 18 , [18][19][20] Ag 24 Pt(SR) 18 , [21] Ag 32 Au 12 (SR) 30 , [22,23] and [Au 12+n Cu 32 (SR) 30+n ] [24] NCs (SR: thiolate). Due to the limitation of synchro-synthesis in obtaining more atomically disperse alloy nanoclusters, a novel synthesis method dubbed antigalvanic reaction (AGR) [25] was introduced by Wu in 2012 and a few atomically disperse alloy nano clusters have been facilely obtained so far, such as Ag 2 Au 25 (SR) 18 , [26] HgAu 24 (SR)…”

“…During the past decade, atomically precise doped nanoclusters (NCs, ultrasmall nanoparticles with size less than ≈2 nm) have gained considerable attention from nanoscientists because of the synergistic or even new properties (e.g., catalytic and optical properties) of doped NCs compared to their homometallic counterparts . A general synthesis method is the synchro‐synthesis (i.e., the mixed metal precursors are concurrently reduced by reducing agent like NaBH 4 ), such as the preparation of Au 24 Pd(SR) 18 , Au 24 Pt(SR) 18 , Au 25− x Ag x (SR) 18 , Au 38− x Ag x (SR) 18 , Au 36 Pd 2 (SR) 18 , Au 36 Pt 2 (SR) 24 , Ag 24 Pd(SR) 18 , Ag 24 Pt(SR) 18 , Ag 32 Au 12 (SR) 30 , and [Au 12+ n Cu 32 (SR) 30+ n ] NCs (SR: thiolate).…”

Atomically Precise Bimetallic Nanoclusters as Photosensitizers in Photoelectrochemical Cells

“…Methods for the sensitization of the semiconductor with these well-characterized metal NCs and measurements of the semiconductor and NCs as aw hole are in demand.O nt he other hand,d emonstrationso fu tilizing metal NCs as photosensitizers have been limitedt ow ater-soluble Au x (x 25) NCs protectedby glutathione( SG). [40][41][42][43] Considering the fact that the vast majority of structurally solved metal NCs are protected by organosoluble ligands( i.e.,t hiol, [44,45] alkyne, [46,47] and phosphine [48,49] ligands), the development of sensitizing the semiconductor with organosoluble metal NCs is vital for elucidating the relationship between the structure of the NCs and the photocatalyticp erformance of the hybrid material.…”