Blue emitting undecaplatinum clusters

The size-dependent valence and conduction band-edge energies of Cu quantum dots

Ultra-small metal particles having band gaps are regarded as a new class of functional materials. We investigated the size dependencies of the band-edge energies on Cu quantum-dots in the size range of 0.7-2.1 nm. The extremely high conduction band-edge energies owing to the strong quantum-size effects were observed for sizes below 1 nm.

Atomically precise structures of Pt2(S-Adam)4(PPh3)2 complexes and catalytic application in propane dehydrogenation

As a bridge between single metal atoms and metal nanoclusters, atomically precise metal complexes are of great significance for controlled synthesis and catalytic applications at the atomic level. Herein, novel Pt₂(S-Adam)₄(PPh₃)₂ complexes were prepared via the conventional synthetic methods of metal nanoclusters. The atomically precise crystal structures of the binuclear Pt complexes with three kinds of packing modes in a unit cell were determined by X-ray crystallography. The two Pt atoms are bridged by two S atoms of thiolates, constructing a rhombus on a plane. Moreover, the ultraviolet visible absorption spectra of Pt₂(S-Adam)₄(PPh₃)₂ complexes show an apparent absorption peak centered at 454 nm. Furthermore, the Pt complexes were used as precursors to prepare catalysts for non-oxidative propane dehydrogenation. The as-prepared Pt-based catalysts with a particle size of approximately 1 nm demonstrated a propane conversion of about 18% and significantly enhanced selectivity for propylene, up to 93%. Our work will be beneficial to the basic understanding of platinum complexes, as well as the improvement of the catalytic dehydrogenation of propane.

Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster

Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron-carbon framework system, have received immense attention due to their different physicochemical properties. We have synthesized ortho-carborane-1,2-dithiol (CBDT) and triphenylphosphine (TPP) coprotected [Ag₄₂(CBDT)₁₅(TPP)₄]^2- (shortly Ag₄₂) using a ligand-exchange induced structural transformation reaction starting from [Ag₁₈H₁₆(TPP)₁₀]²⁺ (shortly Ag₁₈). The formation of Ag₄₂ was confirmed using UV-vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV-vis optical absorption features, which exhibit characteristic patterns, confirmed its molecular nature. Ag₄₂ is the highest nuclearity silver nanocluster protected with carboranes reported so far. Although these clusters are thermally stable up to 200 °C in their solid state, light-irradiation of its solutions in dichloromethane results in its structural conversion to [Ag₁₄(CBDT)₆(TPP)₆] (shortly Ag₁₄). Single crystal X-ray diffraction of Ag₁₄ exhibits Ag₈-Ag₆ core-shell structure of this nanocluster. Other spectroscopic and microscopic studies also confirm the formation of Ag₁₄. Time-dependent mass spectrometry revealed that this light-activated intercluster conversion went through two sets of intermediate clusters. The first set of intermediates, [Ag₃₇(CBDT)₁₂(TPP)₄]^3- and [Ag₃₅(CBDT)₈(TPP)₄]^2- were formed after 8 h of light irradiation, and the second set comprised of [Ag₃₀(CBDT)₈(TPP)₄]^2-, [Ag₂₆(CBDT)₁₁(TPP)₄]^2-, and [Ag₂₆(CBDT)₇(TPP)₇]^2- were formed after 16 h of irradiation. After 24 h, the conversion to Ag₁₄ was complete. Density functional theory calculations reveal that the kernel-centered excited state molecular orbitals of Ag₄₂ are responsible for light-activated transformation. Interestingly, Ag₄₂ showed near-infrared emission at 980 nm (1.26 eV) with a lifetime of >1.5 μs, indicating phosphorescence, while Ag₁₄ shows red luminescence at 626 nm (1.98 eV) with a lifetime of 550 ps, indicating fluorescence. Femtosecond and nanosecond transient absorption showed the transitions between their electronic energy levels and associated carrier dynamics. Formation of the stable excited states of Ag₄₂ is shown to be responsible for the core transformation.

Progress in controlling the synthesis of atomically precise silver nanoclusters

This short review was designed to summarize the advances in synthesis methods of silver nanoclusters.

Red-Fluorescent Pt Nanoclusters for Detecting and Imaging HER2 in Breast Cancer Cells

Overexpression of human epidermal growth factor receptor 2 (HER2) is associated with more frequent cancer recurrence and metastasis. Sensitive sensing of HER2 in living breast cancer cells is crucial in the early stages of cancer and to further understand its role in cells. Biomedical imaging has become an indispensable tool in the fields of early cancer diagnosis and therapy. In this study, we designed and synthesized platinum (Pt) nanocluster bionanoprobes with red emission (Ex/Em = 535/630 nm) for fluorescence imaging of HER2. Our Pt nanoclusters, which were synthesized using polyamidoamine (PAMAM) dendrimer and preequilibration, exhibited approximately 1% quantum yield and possessed low cytotoxicity, ultrasmall size, and excellent photostability. Furthermore, combined with ProteinA as an adapter protein, we developed Pt bionanoprobes with minimal nonspecific binding and utilized them as fluorescent probes for highly sensitive optical imaging of HER2 at the cellular level. More importantly, molecular probes with long-wavelength emission have allowed visualization of deep anatomical features because of enhanced tissue penetration and a decrease in background noise from tissue scattering. Our Pt nanoclusters are promising fluorescent probes for biomedical applications.

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D

Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene.

Atomically precise and monolayer protected iridium clusters in solution

The first atomically precise and monolayer protected iridium cluster in solution, Ir₉(PET)₆ (PET – 2-phenyethanethiol) was synthesized via a solid state method.

Isolation and Tandem Mass Spectrometric Identification of a Stable Monolayer Protected Silver-Palladium Alloy Cluster

A selenolate-protected Ag-Pd alloy cluster was synthesized using a one-pot solution-phase route. The crude product upon chromatographic analyses under optimized conditions gave three distinct clusters with unique optical features. One of these exhibits a molecular peak centered at m/z 2839, in its negative ion mass spectrum assigned to Ag5Pd4(SePh)12(-), having an exact match with the corresponding calculated spectrum. Tandem mass spectrometry of the molecular ion peak up to MS(9) was performed. Complex isotope distributions in each of the mass peaks confirmed the alloy composition. We find the Ag3Pd3(-) core to be highly stable. The composition was further supported by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy.

Reversible formation of Ag₄₄ from selenolates

The cluster Ag₄₄SePh₃₀, originally prepared from silver selenolate, upon oxidative decomposition by H₂O₂ gives the same cluster back, in an apparently reversible synthesis. Such an unusual phenomenon was not seen for the corresponding thiolate analogues. From several characterization studies such as mass spectrometry, Raman spectroscopy, etc., it has been confirmed that the degraded and as-synthesized selenolates are the same in nature, which leads to the reversible process. The possibility of making clusters from the degraded material makes cluster synthesis economical. This observation makes one to consider cluster synthesis to be a reversible chemical process, at least for selenolates.