Glutathione-Stabilized Magic-Number Silver Cluster Compounds

Abstract

Magic-number theories, developed to explain the anomalous stability of clusters in the gas phase, are being successfully applied to explain the stability of families of condensed phase Au clusters. To test the generalizability of these theories, we have synthesized a family of magic-numbered Ag clusters. Silver clusters ligated with glutathione (GSH) were synthesized by reduction of silver glutathiolate in water and then separated by polyacrylamide gel electrophoresis (PAGE). The raw synthetic product consisted of a family of discrete Ag:SG clusters, each forming a band in the PAGE gel. Varying reaction conditions changed the relative abundance of the family members but not their positions and colors within the gel, indicating the molecular precision of magic-number clusters. Absorption onsets for the most abundant clusters monotonically decreased with increasing cluster size, and spectra contained a small number of peaks that corresponded to single electron transitions. Although these Ag:SG clusters are related to Au:SG clusters, the distribution of cluster sizes and the optical absorption spectra were markedly different for the two families. This suggests that the Ag:SG clusters are not a simple extension of the Au:SG system, possibly due to differences in Au and Ag chemistry. Alternatively, condensed-phase magic-number cluster theories may need to be more complex than currently believed.