Polymorphism in magic-sized Au144(SR)60 clusters.

Kirsten M.Ø Jensen,Christopher J Ackerson,Marcus A Tofanelli,Gavin Vaughan,Simon J L Billinge,Christine L Heinecke,Pavol Juhas

doi:10.1038/ncomms11859

Abstract

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. Here we present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. The study reveals structural polymorphism in these archetypal nanoclusters. In addition to confirming the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. The discovery of polymorphism may open up a new dimension in nanoscale engineering.

Highlights

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles
A major challenge, in the majority of cases where the clusters cannot be crystallized, is to determine their structure. We overcome this ‘nanostructure problem’[12] by using atomic pair distribution function (PDF) analysis of X-ray diffraction (XRD) data to study the structure of Au144(SR)[60], one of the largest of the ultra-stable magic-sized clusters with known composition[13,14]
Wong et al.[21] reported 1H-NMR studies of Au144(p-MBA)[60] clusters, which showed only one doublet in the aromatic region of the spectrum, suggesting that all ligands are in symmetry equivalent positions

Summary

Introduction

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. We present the structure of ultra-stable Au144(SR)[60] magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. A major challenge, in the majority of cases where the clusters cannot be crystallized, is to determine their structure We overcome this ‘nanostructure problem’[12] by using atomic pair distribution function (PDF) analysis of X-ray diffraction (XRD) data to study the structure of Au144(SR)[60] (where R is the organic part of the thiol), one of the largest of the ultra-stable magic-sized clusters with known composition[13,14]. Scanning transmission electron microscopy (STEM) studies by Bahena et al.[22] were consistent with the icosahedral core and by introducing the NMR symmetry requirement in theoretical calculations they proposed a symmetrized structure model featuring an equivalent ligand arrangement[22]. The discovery of polymorphism in gold nanoclusters opens up a new dimension in nanoparticle engineering, presenting the a b c d e

Methods

Results

Conclusion