There has been growing interest in gold nanoclusters with well-defined sizes over the past two decades due to their potential applications in catalysis, biology, and nanotechnology. In all the gold clusters that have been structurally characterized, the surface atoms are all coordinated. In order for these complexes to function as catalysts, the ligands have to be removed first, which can modify the cluster core and induce instability. Atom-precise gold clusters with uncoordinated surface sites would allow them to function potentially as in-situ catalysts without any post-synthetic treatments. A tetrahedral Au20 cluster was found previously to be highly stable in the gas phase with all 20 gold atoms on the cluster surface. Preliminary studies showed that it could be stabilized by four phosphine ligands in solution, leaving 16 uncoordinated surface sites. Further efforts to synthesize this unique gold cluster using bidentate phosphines ligands uncovered a size-selectivity. I will report recent progress in my group to synthesize ligand protected Au20 pyramids. Specifically I will discuss our successful synthesis and x-ray structural determination of a new gold cluster: A Au22 cluster coordinated by six long-chain diphosphine ligands, i.e., Au22(L8)6 [L8 = 1,8-bis(diphenylphosphino) octane]. The Au22 cluster core consists of two Au11 units clipped together by four L8 ligands and contains eight uncoordinated surface gold sites. The new Au22(L8)6 nanocluster is unprecedented both in its coordination environment and the core structure. It represents the first ligand-protected atom-precise gold cluster with uncoordinated gold sites, which may be used as in situ catalytic active sites.

From gas phase gold clusters to ligand-protected gold nanoparticles

247th National Meeting (2014)

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