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The use of coordinating solvents in gold cluster synthesis




Compel, W. Scott, author
Ackerson, Christopher J., advisor
Finke, Richard, committee member
Krapf, Diego, committee member
Prieto, Amy, committee member
Reynolds, Melissa, committee member

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Monolayer-protected clusters (MPCs) are nanoparticles ca. 1-3 nm in diameter composed of a metal core and an organic monolayer shell. In this size range MPCs are larger than metal-ligand complexes but too small to exhibit a surface plasmon resonance. The electronic structures of particles in this size regime resemble discrete molecular orbital energy levels as opposed to the band-like behavior observed in larger, plasmonic nanoparticles. MPCs are composed of ten to a few hundred atoms and can be characterized as simple chemical compounds with discrete molecular formulae as opposed to average particle diameters. In these systems, addition or removal of a single metal atom profoundly affects stability and observed properties. This phenomenon gives rise to an exceptionally diverse class of materials with seemingly endless potential evolving from minute compositional changes. Thiolate-protected gold clusters are exemplary MPCs due to their intrinsic high stability that allows for long-term studies and post-synthetic modification. These clusters exhibit unique physiochemical properties that allow for potential applications in electronics, catalysis, biomedicine, and sensing. The past two decades since their discovery brought about a significant body of research regarding the origin of Au cluster properties and total structure elucidation. However, modern approaches for Au cluster synthesis produce polydisperse mixtures of clusters that must undergo extensive postreaction ripening or fractionalization to obtain a pure, single product. New synthetic approaches for monodisperse Au clusters in high yield must be developed before their applications may be realized. The motivation behind this work was to explore the issue of polydispersity in Au cluster synthesis. Through combinatorial screening of synthetic co-solvent systems we find that synthesis in coordinating solvents (i.e., glymes) greatly enhances the monodispersity of Au cluster products. During synthesis, glyme chelates the metal in the metallopolymer precursor and modifies the surface of the resulting particle, resulting in a new series of metastable Au clusters. The synthetic methods presented herein result in pure, single products in high yield. The surface modification brought about by diglyme potentially renders the clusters available for single-ligand functionalization to tailor cluster properties for desired functionality. The products are evaluated for biomedical and sensing applications.


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