Chemistry and Structure of Silver Molecular Nanoparticles

Abstract

CONSPECTUS: Silver and gold molecular nanoparticles (mNPs) are a relatively new class of molecular materials of fundamental interest. They are high-nuclearity metal−organic compounds, with ligated metal cores, where the different character of bonding in the ligand shell and metal core gives rise to many of the unique properties of these materials. Research has primarily focused on gold mNPs, due to their good stability and the ease with which they may be synthesized and processed. To understand these materials as a general class, however, it will be necessary to broaden research efforts to other metals. Gold and silver are isoelectronic and have the same atomic radius, making the comparison of gold and silver mNPs attractive. The optical and chemical differences of the two metals provide useful contrasts, however, as well as a means to access a wider range of properties. In this Account, we focus on the synthesis, structure, and reactivity of silver mNPs. First, we review the origins and history of the field, from the ill-defined gas-phase metal clusters of the 1980s to the precisely defined mNPs of 1996 and onward. Next, we discuss the role of silver as a complement to gold mNPs in the effort to generalize lessons learned from either material and extend them into new metals. The synthesis of silver mNPs is covered in some detail, noting the choices made as the chemistry and the materials were developed. The importance of coordinating solvents and thermodynamic stability are also noted. The need to reduce solvent use is discussed and a new approach to achieving this goal is presented. Next, the structures of silver mNPs are discussed, including the Ag 44 and Ag 17 archetypes, and focusing on the successful de novo structure prediction of the latter. Structure and prediction of ligand shell motifs are also discussed. Finally, the postsynthetic chemistry and reactivity of silver mNPs are presented, including some of the first efforts to elucidate reaction mechanisms, beginning in 2012. Silver nanoparticles are gaining in popularity, particularly compared with gold, as the potential for silver to make a technological and economic impact is recognized. The superior optical properties of silver already make it a valuable material for plasmonics, but this may also translate to molecular species for nonlinear optics, sensors, and optoelectronics. The higher reactivity may also lead to a greater diversity of chemistry for silver compared to gold, including as an important broad-spectrum antimicrobial. Conversely, the "ultrastability" of the Ag 44 archetype has already enabled unprecedented scale up with molecular precision, and may lead to the first industrial-scale production of metal mNPs. Clearly, silver mNPs are one of the most promising and significant new materials being studied today.

Rendering hydrophobic nanoclusters water-soluble and biocompatible

“…Metal nanoclusters, beneting from their atomically precise structures, fascinating properties, and potential applications, are an emerging class of modular nanomaterials. [1][2][3][4][5][6][7][8][9][10][11] Recent years have witnessed signicant research efforts on the controllable synthesis and the structural determination of metal nanoclusters. Typically, the great nanocluster family encompasses both hydrophobic and hydrophilic clusters.…”

“…1 Based on such knowledge and understanding of mechanisms underlying cluster performances, several efficient approaches have been put forward to accurately dictate the chemicalphysical performances of metal nanoclusters. [1][2][3][4][5][6][7][8][9][10][11][35][36][37][38][39][40][41][42] However, in consideration of their hydrophobicity, these nanoclusters are less likely directly applicable to water-phase applications, such as chemical sensing, bio-imaging, bio-labeling, and biotherapy, to name a few.…”

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

“…Mid‐way in size between discrete metal complexes and nanoparticles, ultrasmall (<2 nm) metal nanoclusters (NCs) comprising several to hundreds of metal atoms have attracted a great deal of interest due to their molecular‐like properties, such as fluorescence and chirality . With the ongoing determination of their precise structures (e.g., by single‐crystal X‐ray diffraction), some fantastic structural correlations with atomic packing modes have been elucidated . For example, Au 13 , Au 25 , and Au 37 comprising one to three icosahedral building blocks have been successfully prepared and well characterized.…”

“…Mid-wayi ns ize betweendiscrete metalc omplexesa nd nanoparticles, [1][2][3][4] ultrasmall (< 2nm) metal nanoclusters( NCs) comprising several to hundreds of metal atoms have attracted a great deal of interest due to their molecular-like properties, [5][6][7][8][9][10][11] such as fluorescence [5,6] and chirality. [7][8][9][10] With the ongoing determination of their precise structures (e.g.,b ys ingle-crystal Xray diffraction), some fantastic structural correlationsw ith atomic packingm odes have been elucidated.…”

“…[7][8][9][10] With the ongoing determination of their precise structures (e.g.,b ys ingle-crystal Xray diffraction), some fantastic structural correlationsw ith atomic packingm odes have been elucidated. [1][2][3][4][12][13][14] For example, Au 13 , [15,16] Au 25 , [17,18] and Au 37 [19] comprising one to three icosahedralb uilding blocks have been successfully prepared and well characterized. Similarly,t he regular assembly of different numbers of tetrahedral M 4 blocks through vertex-sharing has been reported in the thiolate-protected NCs Au 28 (SR) 20 , [7,20] Au 36 (SR) 24 , [21] Au 44 (SR) 28 ,a nd Au 52 (SR) 32 .…”