Golden probe: Opening the cluster

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  • Published: Apr 15, 2019
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Golden probe: Opening the cluster

Perfect phosphorus probe

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy was the

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy was the "perfect probe" in a study of a ligand-protected golden fullerene, according to research published in Angewandte Chemie.

Shang-Fu Yuan , Cong-Qiao Xu , Jun Li, and Quan-Ming Wang of Tsinghua University in Beijing, China describe a golden "ball" in a golden "cage": a 12-atom gold nanocluster within a 20-atom gold nanocluster all held together with amido and phosphine ligands bound to its surface. The structure has unusual stability thanks to the interactions between the nitrogen-containing amido components and the phosphorus-containing ligands.

Aggregation, the name of the game

Aggregates of a few metal atoms, commonly known as clusters, are of growing interest for applications in catalysis, bioscience, and nanotechnology, although their existence and intriguing properties that deviate markedly from the bulk element have been known about for many years. However, once chemists had built a pyramidal structure of 20 gold atoms, which they dubbed a “golden cage” this new class of clusters with unusual structural properties was predicted to become even more useful if there were the possibility of making even bigger clusters, say of 32 gold atoms. Structurally, such an entity might be regarded as a precious metal analogue of the all-carbon molecule, fullerene-60, once colloquially known as the buckyball. That said, without the ligand support, such a gold cluster would not be stable unlike the buckyball whose pentagonal and hexagonal faces are sufficient to keep the perfectly symmetrical truncated icosahedron intact. Nevertheless, “golden fullerenes” are predicted to have a broad spectrum of possible applications as transporters, molecular labels, and catalysts.

Li and Wang and their team have now synthesised the sough-after gold nanocluster in solution. The synthesis involved the direct reduction of gold-containing precursors. The final structure has the formula [Au32(Ph3P)8(dpa)6]+[SbF6-]2 (where dpa = 2,2'-bipyridylamido ligand and Ph3P = triphenylphosphine ligand). The Au12@Au20 structure is protected by eight Ph3P and six dpa ligands bound to its surface. The team used various analytical methods, including the aforementioned NMR, as well as computer calculations to obtain a complete structural determination of its geometry, its chemical bonding relationships, and its electronic structure.

The “golden core” of the new cluster compound, they explain, is a hollow icosahedron (a regular solid with 20 triangular faces) encased by the shell of 20 gold atoms forming a dodecahedron (a regular solid with 12 pentagonal faces). The bonds between the shell and core are very strong. The eight Ph3P ligands are bound to eight gold atoms of the shell, forming the corners of a cube, the team found. The dpa ligands are arranged so that their mid-points form the vertices of an octahedron. They are not bound through their amido groups, but instead through the two nitrogen atoms in their two aromatic rings, which each bridge two gold atoms.


“The geometric and electronic structures of the gold cluster depend very strongly on interactions with the ligands, as confirmed by our quantum chemical studies,” the researchers explain. “The dpa ligands in particular ensure the effective stabilization of the gold nanocluster. We anticipate that a rich variety of coinage-metal nanoclusters can be generated with the protection of amido ligands.”

An independent team led by Andreas Schnepf of the University of Tübingen in Germany and Howard University in Washington DC, the University of Missouri, Kansas City, USA, have also recently reported a synthesis of a similar nanocluster containing 32 gold atoms.

Related Links

Angew Chem Int Edn Engl 2019, online: "A Ligand-Protected Golden Fullerene: The Dipyridylamido Au32 8+ Nanocluster"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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