Brian E. Conn

Ultrastable silver nanoparticles

Noble-metal nanoparticles have had a substantial impact across a diverse range of fields, including catalysis, sensing, photochemistry, optoelectronics, energy conversion and medicine. Although silver has very desirable physical properties, good relative abundance and low cost, gold nanoparticles have been widely favoured owing to their proved stability and ease of use. Unlike gold, silver is notorious for its susceptibility to oxidation (tarnishing), which has limited the development of important silver-based nanomaterials. Despite two decades of synthetic efforts, silver nanoparticles that are inert or have long-term stability remain unrealized. Here we report a simple synthetic protocol for producing ultrastable silver nanoparticles, yielding a single-sized molecular product in very large quantities with quantitative yield and without the need for size sorting. The stability, purity and yield are substantially better than those for other metal nanoparticles, including gold, owing to an effective stabilization mechanism. The particular size and stoichiometry of the product were found to be insensitive to variations in synthesis parameters. The chemical stability and structural, electronic and optical properties can be understood using first-principles electronic structure theory based on an experimental single-crystal X-ray structure. Although several structures have been determined for protected gold nanoclusters, none has been reported so far for silver nanoparticles. The total structure of a thiolate-protected silver nanocluster reported here uncovers the unique structure of the silver thiolate protecting layer, consisting of Ag2S5 capping structures. The outstanding stability of the nanoparticle is attributed to a closed-shell 18-electron configuration with a large energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, an ultrastable 32-silver-atom excavated-dodecahedral core consisting of a hollow 12-silver-atom icosahedron encapsulated by a 20-silver-atom dodecahedron, and the choice of protective coordinating ligands. The straightforward synthesis of large quantities of pure molecular product promises to make this class of materials widely available for further research and technology development.

Confirmation of a de novo structure prediction for an atomically precise monolayer-coated silver nanoparticle

A predicted structure of an organically capped silver nanocluster is confirmed via x-ray diffraction and ab initio theory. Fathoming the principles underpinning the structures of monolayer-coated molecular metal nanoparticles remains an enduring challenge. Notwithstanding recent x-ray determinations, coveted veritable de novo structural predictions are scarce. Building on recent syntheses and de novo structure predictions of M3AuxAg17−x(TBBT)12, where M is a countercation, x = 0 or 1, and TBBT is 4-tert-butylbenzenethiol, we report an x-ray–determined structure that authenticates an a priori prediction and, in conjunction with first-principles theoretical analysis, lends force to the underlying forecasting methodology. The predicted and verified Ag(SR)3 monomer, together with the recently discovered Ag2(SR)5 dimer and Ag3(SR)6 trimer, establishes a family of unique mount motifs for silver thiolate nanoparticles, expanding knowledge beyond the earlier-known Au-S staples in thiol-capped gold nanoclusters. These findings demonstrate key principles underlying ligand-shell anchoring to the metal core, as well as unique T-like benzene dimer and cyclic benzene trimer ligand bundling configurations, opening vistas for rational design of metal and alloy nanoparticles.

M4Au12Ag32(p-MBA)30 (M = Na, Cs) bimetallic monolayer-protected clusters: synthesis and structure

The synthesis and structure of mixed gold/silver M 4Au12Ag32(p-MBA)30 bimetallic monolayer-protected clusters is reported and compared to that of silver M 4Ag44(p-MBA)30 monolayer-protected clusters (M = Na, Cs).

CHAPTER 3:Silver Magic-Number Clusters and Their Properties

Metal nanoparticles between 5–100 nm have received the most attention due to their ease of synthesis and characterization. Below 3 nm, however, the electronic and atomic structure of metal nanoparticles can become discretized, producing families of magic-number clusters and a new regime of molecular behavior. While this regime can include unique new phenomena such as Au cluster catalysis and efficient metal cluster fluorescence, it can also provide deep fundamental insights into the origin and emergence of metallic properties as well as nanostructure stability. Gold has been the model system for addressing most of these questions, however in many cases it is not sufficient to rely on gold alone. Recent advances in the chemical preparation and identification of magic-number Ag clusters have provided a new system in which to test our current understanding of metal cluster properties. This review will focus on the development of Ag magic-number clusters as a new and complementary effort in cluster science. We will review the chemical synthesis of these molecular materials, their separations, and their characterization. Special emphasis will be placed on electrospray-ionization mass spectrometric characterization of these delicate species. The optical properties of Ag clusters will also be reviewed in detail.