The Superstable 25 kDa Monolayer Protected Silver Nanoparticle: Measurements and Interpretation as an Icosahedral Ag152(SCH2CH2Ph)60 Cluster

A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH2CH2Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well-defined. metal core of similar to 2 nm measured with transmission electron microscopy (TEM). The Cluster yields a single fraction in high-performance-liquid. chromatography (HPLC). Increased laser fluence fragments the cluster Until a. new peak near,19 kDa predominates suggesting that the parent cluster-Ag-152(SCH2CH2Ph)(60)-evolves into a stable inorganic core-Ag152S60 Exploiting combined insights from investigations clusters. And surface science a tore-shell structure,model was developed, with a 92 atom silver Core having icosahedral-dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 66 thiolates arranged in a network of six-memberedrings resembling the geometry found in self assembled monolayers on Ag(111). The structure is in agreement with small angle X-ray scattering (SAXS) data The protective layer encapsulating this silver cluster may be the smallest known three-dimensional self-assembled monolayer. First principles electronic structure calculations show, for the geometry-optimized structure, the development of a similar to 0.4 eV energy gap between the highest occupied and lowest unoccupied states, originating from. a superatom 90 electron shell closure and conferring stability to the cluster. The optical absorption spectrum of the cluster resembles that of plasmonic silver nanoparticles with a broad single. feature peaking at 466 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core.