Atomically precise nanoclusters of coinage metals in the 1–3 nm size regime have been intensively pursued in recent years. Such nanoclusters are attractive as they fill the gap between small molecules (<1 nm) and regular nanoparticles (>3 nm). This intermediate identity endows nanoclusters with unique physicochemical properties and provides nanochemists opportunities to understand the fundamental science of nanomaterials. Metal nanoparticles are well known to exhibit plasmon resonances upon interaction with light; however, when the particle size is downscaled to the nanocluster regime, the plasmons fade out and step-like absorption spectra characteristic of cluster sizes are manifested due to strong quantum confinement effects. Recent research has revealed that nanoclusters are commonly composed of a distinctive kernel and a surface-protecting shell (or staple-like metal–ligand motifs). Understanding the kernel configuration and evolution is one of the central topics in nanoscience research. This Review summarizes the recent progress in identifying the growth patterns of atomically precise coinage nanoclusters. Several basic kernel units have been observed, such as the M 4 , M 13 and M 14 polyhedrons (where, M = metal atom). Among them, the tetrahedral M 4 and icosahedral M 13 units are the most common ones, which are adopted as building blocks to construct larger kernel structures via various fusion or aggregation modes, including the vertex- and face-sharing mode, the double-strand and alternate single-strand growth, and cyclic fusion of units, as well as the fcc-based cubic growth pattern. The identification of the kernel growth pathways has led to deeper understanding of the evolution of electronic structure and optic properties.
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Atomic-precision engineering of metal nanoclusters
Ultrasmall metal nanoparticles (below 2.2 nm core diameter) start to show discrete electronic energy levels due to strong quantum confinement effects and thus behave much like molecules. The size and structure dependent quantization induces a plethora of new phenomena, including multi-band optical absorption, enhanced luminescence, single-electron magnetism, and catalytic reactivity. The exploration of such new properties is largely built on the success in unveiling the crystallographic structures of atomically precise nanoclusters (typically protected by ligands, formulated as M n L m q , where M = metal, L = Ligand, and q = charge). Correlation between the atomic structures of nanoclusters and their properties has further enabled atomic-precision engineering toward materials design. In this frontier article, we illustrate several aspects of the precise engineering of gold nanoclusters, such as the single-atom size augmenting, single-atom dislodging and doping, precise surface modification, and single-electron control for magnetism. Such precise engineering involves the nanocluster's geometric structure, surface chemistry, and electronic properties, and future endeavors will lead to new materials design rules for structure–function correlations and largely boost the applications of metal nanoclusters in optics, catalysis, magnetism, and other fields. Following the illustrations of atomic-precision engineering, we have also put forth some perspectives. We hope this frontier article will stimulate research interest in atomic-level engineering of nanoclusters.
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- Award ID(s):
- 1808675
- NSF-PAR ID:
- 10228312
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 49
- Issue:
- 31
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 10701 to 10707
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1–3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X‐ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum‐confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold‐thiolate nanoclusters (Au
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The transition from the discrete, excitonic state to the continuous, metallic state in thiolate-protected gold nanoclusters is of fundamental interest and has attracted significant efforts in recent research. Compared with optical and electronic transition behavior, the transition in magnetism from the atomic gold paramagnetism (Au 6s 1 ) to the band behavior is less studied. In this work, the magnetic properties of 1.7 nm [Au 133 (TBBT) 52 ] 0 nanoclusters (where TBBT = 4- tert -butylbenzenethiolate) with 81 nominal “valence electrons” are investigated by electron paramagnetic resonance (EPR) spectroscopy. Quantitative EPR analysis shows that each cluster possesses one unpaired electron (spin), indicating that the electrons fill into discrete orbitals instead of a continuous band, for that one electron in the band would give a much smaller magnetic moment. Therefore, [Au 133 (TBBT) 52 ] 0 possesses a nonmetallic electronic structure. Furthermore, we demonstrate that the unpaired spin can be removed by oxidizing [Au 133 (TBBT) 52 ] 0 to [Au 133 (TBBT) 52 ] + and the nanocluster transforms from paramagnetism to diamagnetism accordingly. The UV-vis absorption spectra remain the same in the process of single-electron loss or addition. Nuclear magnetic resonance (NMR) is applied to probe the charge and magnetic states of Au 133 (TBBT) 52 , and the chemical shifts of 52 surface TBBT ligands are found to be affected by the spin in the gold core. The NMR spectrum of Au 133 (TBBT) 52 shows a 13-fold splitting with 4-fold degeneracy of 52 TBBT ligands, which are correlated to the quasi- D 2 symmetry of the ligand shell. Overall, this work provides important insights into the electronic structure of Au 133 (TBBT) 52 by combining EPR, optical and NMR studies, which will pave the way for further understanding of the transition behavior in metal nanoclusters.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0dt01853h
