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.