The superstable 25 kDa monolayer protected silver nanoparticle: Measurements and interpretation as an icosahedral Ag152(SCH 2CH2Ph)60 cluster

Indranath Chakraborty, Anuradha Govindarajan, Jayanthi Erusappan, Atanu Ghosh, T. Pradeep, Bokwon Yoon, Robert L. Whetten, Uzi Landman

Research output: Contribution to journalArticlepeer-review

122 Scopus citations


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 ∼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-Ag152(SCH2CH2Ph)60-evolves into a stable inorganic core-Ag152S60. Exploiting combined insights from investigations of clusters and surface science, a core-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 60 thiolates arranged in a network of six-membered rings 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 ∼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 460 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core.

Original languageEnglish (US)
Pages (from-to)5861-5866
Number of pages6
JournalNano Letters
Issue number11
StatePublished - Nov 14 2012
Externally publishedYes


  • Noble metals
  • clusters
  • first-principles electronic structure
  • nanoparticles
  • plasmon resonance
  • projected electronic density of states (PDOS)
  • superatom electronic shells

ASJC Scopus subject areas

  • Bioengineering
  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanical Engineering


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