A molecule-like PtAu24(SC6H13)18 nanocluster as an electrocatalyst for hydrogen production

The geometric and electronic structures of a Ag13Cu10(SAdm)12X3 nanocluster

Herein, we report the synthesis and total structure of a Cu-rich alloy nanocluster protected by twelve adamantanethiolate ligands, i.e., [Ag₁₃Cu₁₀(SAdm)₁₂]X₃ (-SAdm = SC₁₀H₁₅, X = counterion), which was confirmed by single-crystal X-ray structure determination and electrospray ionization mass spectrometry (ESI-MS). X-ray crystallographic analysis indicated that [Ag₁₃Cu₁₀(SAdm)₁₂]X₃ consisted of an icosahedral Ag₁₃ core, covered by a cage-like shell of Cu₁₀(SAdm)₁₂. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the geometric and electronic structures and KS orbitals and UV-vis spectroscopy were performed on the model [Ag₁₃Cu₁₀(SMe)₁₂]³⁺ and its monometallic analog [Ag₂₃(SMe)₁₂]³⁺. This work will deepen the understanding of core-shell Ag-Cu alloy nanoclusters.

Molecular reactivity of thiolate-protected noble metal nanoclusters: synthesis, self-assembly, and applications

Thiolate-protected noble metal (e.g., Au and Ag) nanoclusters (NCs) are ultra-small particles with a core size of less than 3 nm. Due to the strong quantum confinement effects and diverse atomic packing modes in this ultra-small size regime, noble metal NCs exhibit numerous molecule-like optical, magnetic, and electronic properties, making them an emerging family of "metallic molecules". Based on such molecule-like structures and properties, an individual noble metal NC behaves as a molecular entity in many chemical reactions, and exhibits structurally sensitive molecular reactivity to various ions, molecules, and other metal NCs. Although this molecular reactivity determines the application of NCs in various fields such as sensors, biomedicine, and catalysis, there is still a lack of systematic summary of the molecular interaction/reaction fundamentals of noble metal NCs at the molecular and atomic levels in the current literature. Here, we discuss the latest progress in understanding and exploiting the molecular interactions/reactions of noble metal NCs in their synthesis, self-assembly and application scenarios, based on the typical M(0)@M(i)-SR core-shell structure scheme, where M and SR are the metal atom and thiolate ligand, respectively. In particular, the continuous development of synthesis and characterization techniques has enabled noble metal NCs to be produced with molecular purity and atomically precise structural resolution. Such molecular purity and atomically precise structure, coupled with the great help of theoretical calculations, have revealed the active sites in various structural hierarchies of noble metal NCs (e.g., M(0) core, M-S interface, and SR ligand) for their molecular interactions/reactions. The anatomy of such molecular interactions/reactions of noble metal NCs in synthesis, self-assembly, and applications (e.g., sensors, biomedicine, and catalysis) constitutes another center of our discussion. The basis and practicality of the molecular interactions/reactions of noble metal NCs exemplified in this Review may increase the acceptance of metal NCs in various fields.

Dynamics of Pd Dopant Atoms inside Au Nanoclusters during Catalytic CO Oxidation

Doping gold nanoclusters with palladium has been reported to increase their catalytic activity and stability. PdAu24 nanoclusters, with the Pd dopant atom located at the center of the Au cluster core, were supported on titania and applied in catalytic CO oxidation, showing significantly higher activity than supported monometallic Au25 nanoclusters. After pretreatment, operando DRIFTS spectroscopy detected CO adsorbed on Pd during CO oxidation, indicating migration of the Pd dopant atom from the Au cluster core to the cluster surface. Increasing the number of Pd dopant atoms in the Au structure led to incorporation of Pd mostly in the S-(M-S) n protecting staples, as evidenced by in situ XAFS. A combination of oxidative and reductive thermal pretreatment resulted in the formation of isolated Pd surface sites within the Au surface. The combined analysis of in situ XAFS, operando DRIFTS, and ex situ XPS thus revealed the structural evolution of bimetallic PdAu nanoclusters, yielding a Pd single-site catalyst of 2.7 nm average particle size with improved CO oxidation activity.

Not Completely Innocent: How Argon Binding Perturbs Cationic Copper Clusters

Argon is often considered as an innocent probe that can be attached and detached to study the structure of a particular species without perturbing the species too much. We have investigated whether this assumption also holds for small copper cationic clusters and demonstrated that small but significant charge transfer from argon to metal changes the remaining binding positions, leading in general, to weaker binding of other argon atoms. The exception is binding to just one copper ion, where the binding of the first argon facilitates the binding of the second.

Composition-Dependent Antimicrobial Ability of Full-Spectrum AuxAg25-x Alloy Nanoclusters

Alloying is an efficient chemistry to diversify the properties of metal nanoparticles; however, the atomic-level understandings of the composition-dependent physicochemical properties and their related biological performance are presently lacking. Here, we developed a full spectrum of alloy metal nanoclusters (NCs), Au_xAg_25-x(MHA)₁₈ (MHA = 6-mercaptohexanoic acid) with x = 0-25, and investigated their composition-dependent antimicrobial performance. Interestingly, we observed a U-shape antimicrobial behavior of Au_xAg_25-x(MHA)₁₈ NCs, where the alloy NCs showed decreased antimicrobial ability instead of the common trend of increasing. Detailed atomic-level characterizations of the AuAg NCs suggest that the decreased performance of alloy NCs is due to their enhanced stability after alloying, which can deactivate their capability in generating reactive oxygen species (ROS) that can kill the bacteria. More interestingly, the transition point of the antimicrobial performance was only obtained with our full-spectrum Au_xAg_25-x(MHA)₁₈ NCs, which indicates the importance of exploring the composition-dependent properties and application performance in a full-spectrum composition range. A library of full-spectrum alloy NCs also provides a good platform to investigate other composition-dependent physicochemical and biological properties of metal NCs.

Reactivity and Lability Modulated by a Valence Electron Moving in and out of 25-Atom Gold Nanoclusters

The emergence of atomically precise metal nanoclusters with unique electronic structures provides access to currently inaccessible catalytic challenges at the single-electron level. We investigate the catalytic behavior of gold Au₂₅ (SR)₁₈ nanoclusters by monitoring an incoming and outgoing free valence electron of Au 6s¹ . Distinct performances are revealed: Au₂₅ (SR)₁₈ ^- is generated upon donation of an electron to neutral Au₂₅ (SR)₁₈ ⁰ and this is associated with a loss in reactivity, whereas Au₂₅ (SR)₁₈ ⁺ is generated from dislodgment of an electron from neutral Au₂₅ (SR)₁₈ ⁰ with a loss in stability. The reactivity diversity of the three Au₂₅ (SR)₁₈ clusters stems from different affinities with reactants and the extent of intramolecular charge migration during the reactions, which are closely associated with the valence occupancies of the clusters varied by one electron. The stability difference in the three clusters is attributed to their different equilibria, which are established between the AuSR dissociation and polymerization influenced by one electron.

Hydrogen in Nanocatalysis

Hydrogen is ubiquitous in catalysis. It is involved in many important reactions such as water splitting, N₂ reduction, CO₂ reduction, and alkane activation. In this Perspective, we focus on the hydrogen atom and follow its electron as it interacts with a catalyst or behaves as part of a catalyst from a computational point of view. We present recent examples in both nanocluster and solid catalysts to elucidate the parameters governing the strength of the hydrogen-surface interactions based on site geometry and electronic structure. We further show the interesting behavior of hydride in nanometal and oxides for catalysis. The key take-home messages are: (1) the in-the-middle electronegativity and small size of hydrogen give it great versatility in interacting with active sites on nanoparticles and solid surfaces; (2) the strength of hydrogen binding to an active site on a surface is an important descriptor of the chemical and catalytic properties of the surface; (3) the energetics of the hydrogen binding is closely related to the electronic structure of the catalyst; (4) hydrides in nanoclusters and oxides and on surfaces offer unique reactivity for reduction reactions.

Atomically precise alloy nanoclusters: syntheses, structures, and properties

Metal nanoclusters fill the gap between discrete atoms and plasmonic nanoparticles, providing unique opportunities for investigating the quantum effects and precise structure-property correlations at the atomic level. As a versatile strategy, alloying can largely improve the physicochemical performances compared to the corresponding homo-metal nanoclusters, and thus benefit the applications of such nanomaterials. In this review, we highlight the achievements of atomically precise alloy nanoclusters, and summarize the alloying principles and fundamentals, including the synthetic methods, site-preferences for different heteroatoms in the templates, and alloying-induced structure and property changes. First, based on various Au or Ag nanocluster templates, heteroatom doping modes are presented. The templates with electronic shell-closing configurations tend to maintain their structures during doping, while the others may undergo transformation and give rise to alloy nanoclusters with new structures. Second, alloy nanoclusters of specific magic sizes are reviewed. The arrangement of different atoms is related to the symmetry of the structures; that is, different atoms are symmetrically located in the nanoclusters of smaller sizes, and evolve into shell-by-shell structures at larger sizes. Then, we elaborate on the alloying effects in terms of optical, electrochemical, electroluminescent, magnetic and chiral properties, as well as the stability and reactivity via comparisons between the doped nanoclusters and their homo-metal counterparts. For example, central heteroatom-induced photoluminescence enhancement is emphasized. The applications of alloy nanoclusters in catalysis, chemical sensing, bio-labeling, and other fields are further discussed. Finally, we provide perspectives on existing issues and future efforts. Overall, this review provides a comprehensive synthetic toolbox and controllable doping modes so as to achieve more alloy nanoclusters with customized compositions, structures, and properties for applications. This review is based on publications available up to February 2020.

The precise editing of surface sites on a molecular-like gold catalyst for modulating regioselectivity

It is extremely difficult to precisely edit a surface site on a typical nanoparticle catalyst without changing other parts of the catalyst. This precludes a full understanding of which site primarily determines the catalytic properties. Here, we couple experimental data collection with theoretical analysis to correlate rich structural information relating to atomically precise gold clusters with the catalytic performance for the click reaction of phenylacetylene and benzyl azide. We also identify a specific surface site that is capable of achieving high regioselectivity. We further conduct site-specific editing on a thiolate-protected gold cluster by peeling off two monomeric RS–Au–SR motifs and replacing them with two Ph₂P–CH₂–PPh₂ staples. We demonstrate that the surface Au–Ph₂P–CH₂–PPh₂–Au motifs enable extraordinary regioselectivity for the click reaction of alkyne and azide. The editing strategy for the surface motifs allows us to exploit previously inaccessible individual active sites and elucidate which site can explicitly govern the reaction outcome.

Editing surface motifs on gold cluster catalysts achieves high regioselectivity for the click reactions of azides and alkynes.

An Au8 Cluster Fortified by Four Ferrocenes

Atomically precise metal clusters are now in the research spotlight, owing to the precise correlation between the physicochemical properties and their atomic-packing structures at an atomic-level. Herein we synthesized an Au₈ cluster capped by four ferrocene ligands (DPPF), in which the ferrocene not only can direct the precise formation of the Au₈ cluster, but also can solidify the structural pattern of the Au₈ cluster. The Au₈(DPPF)₄ clusters as heterogeneous catalysts can achieve efficiently catalytic performances for the CO oxidation reaction, mainly due to the resistance to aggregation into large particles under reaction conditions. Our results suggest that the homolytic phosphine dissociation nature and the postdissociation reconstruction effect induced by Fe may enhance the catalytic performances of Au₈(DPPF)₄.

Gold nanoclusters as electrocatalysts: size, ligands, heteroatom doping, and charge dependences

To establish an ultimate energy conversion system consisting of a water-splitting photocatalyst and a fuel cell, it is necessary to further increase the efficiencies of the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR). Recently, it was demonstrated that thiolate (SR)-protected gold clusters, Aun(SR)m, and their related alloy clusters can serve as model catalysts for these three reactions. However, as the previous data have been obtained under different experimental conditions, it is difficult to use them to gain a deep understanding of the means to attain higher activity in these reactions. Herein, we measured the HER, OER, and ORR activities of Aun(SR)m and alloy clusters containing different numbers of constituent atoms, ligand functional groups, and heteroatom species under identical experimental conditions. We obtained a comprehensive set of results that illustrates the effect of each parameter on the activities of the three reactions. Comparison of the series of results revealed that decreasing the number of constituent atoms in the cluster, decreasing the thickness of the ligand layer, and substituting Au with Pd improve the activities in all reactions. Taking the stability of the cluster into consideration, [Au24Pd(PET)18]0 (PET = 2-phenylethanethiolate) can be considered as a metal cluster with high potential as an HER, OER, and ORR catalyst. These findings are expected to provide clear design guidelines for the development of highly active HER, OER, and ORR catalysts using Aun(SR)m and related alloy clusters, which would allow realization of an ultimate energy conversion system.

Rendering hydrophobic nanoclusters water-soluble and biocompatible

Hydrophobic and hydrophilic nanoclusters embody complementary superiorities. The means to amalgamate these superiorities, i.e., the atomic precision of hydrophobic clusters and the water dissolvability of hydrophilic clusters, remains challenging. This work presents a versatile strategy to render hydrophobic nanoclusters water-soluble-the micellization of nanoclusters in the presence of solvent-conjoined Na+ cations-which overcomes the above major challenge. Specifically, although [Ag29(SSR)12(PPh3)4]3- nanoclusters are absolutely hydrophobic, they show good dissolvability in aqueous solution in the presence of solvent-conjoined Na+ cations (Na1(NMP)5 or Na3(DMF)12). Such cations act as both counterions of these nanoclusters and surface cosolvent of cluster-based micelles in the aqueous phase. A combination of DLS (dynamic light scattering) and aberration-corrected HAADF-STEM (high angle annular dark field detector scanning transmission electron microscopy) measurements unambiguously shows that the phase-transfer of hydrophobic Ag29 into water is triggered by the micellization of nanoclusters. Owing to the excellent water solubility and stability of [Ag29(SSR)12(PPh3)4]3-[Na1(NMP)5]3 + in H2O, its performance in cell staining has been evaluated. Furthermore, the general applicability of the micellization strategy has been verified. Overall, this work presents a convenient and efficient approach for the preparation of cluster-based, biocompatible nanomaterials.

Doping Copper Atoms into the Nanocluster Kernel: Total Structure Determination of [Cu30Ag61(SAdm)38S3](BPh4)

Doping active metal (i.e., Cu) into the kernel of noble metal nanoclusters (i.e., Au/Ag nanocluster) remains challenging in the synthesis of alloy nanoclusters. Herein, we report the synthesis and the total structure determination of a bimetallic [Ag₆₁Cu₃₀(SAdm)₃₈S₃]BPh₄ (Ag₆₁Cu₃₀) nanocluster. The Ag₆₁Cu₃₀ nanocluster is composed of an Ag₁₃@Cu₃₀ kernel which is further capped by a peripheral Ag₄₈(SAdm)₃₈S₃ shell. The icosidodecahedron Cu₃₀ middle layer connects the innermost icosahedral Ag₁₃ core and Ag atoms at the outermost Ag₄₈(SR)₃₈S₃ shell, demonstrating that the Cu atoms in the Cu₃₀ layer are in a metallic state.

Effect of subtle changes of isomeric ligands on the synthesis of atomically precise water-soluble gold nanoclusters

The subtle structural change of hydrophilic ligands on the size control of metal nanoclusters (NCs) is unclear but critically important for fundamental understanding. Herein, we report our findings that subtle changes of isomeric ligands lead to a dramatic difference in the size of water-soluble Au NCs. By using isomeric para-mercaptobenzoic acid (p-MBA), m-MBA, and o-MBA as model ligands, it was found that both the steric hindrance and the electronic effect of isomeric ligands significantly influences the size of Au NCs, resulting in the formation of different sized Au44(p-MBA)26 NCs, Au25(m-MBA)18 NCs, and Au37/43(o-MBA)22/26 NCs. Besides this, by collocating any two of the isomeric MBAs as ligand pairs to compare their protecting capability for Au NCs, the protecting abilities of such ligands were found to follow the trend: m-MBA > o-MBA > p-MBA. In addition, the growth process of Au44(p-/o-MBA)26 NCs from Au(i)-MBA complexes in the NaBH4 reduction system was also monitored by real-time UV-vis absorption spectroscopy and ESI mass spectrometry, which complies with the 2e- hopping growth principle, indicating the universal applicability of this principle in the synthesis of thiolated metal NCs. This study provides a fundamental understanding of the effect of ligands' steric hindrance and electronic factors on the size control of water-soluble metal NCs and sheds light on the formation of metal NCs in the NaBH4 reduction system.

Unlocking the catalytic activity of an eight-atom gold cluster with a Pd atom

It remains elusive as to how exactly the site-specific atom in a catalyst can induce a chemical reaction mainly due to the observed catalytic performance from an ensemble average of all active atoms in the catalyst. In this work, we have reported the catalytic properties of four metal clusters (namely, Au₈Pd, Au₉, Au₂₄Pd and Au₂₅) for the oxidation of benzyl alcohol. It was found that the Pd atom in the Au₈Pd cluster is likely to be a key to catalyze the oxidation reaction, in which the Pd atom can provide an active site to adsorb and activate O₂. Our calculation study suggests that the high catalytic activity of the Au₈Pd cluster is due to the unique ability of Au₈Pd to mediate the electrons and holes of the adsorbates. This work provides a feasible strategy to enable highly efficient chemical processes via precisely doping foreign atoms into catalysts with atomic precision.

Miscible-Solvent-Assisted Two-Phase Synthesis of Monolayer-Ligand-Protected Metal Nanoclusters with Various Sizes

Effective yet versatile synthetic strategies for size-tunable metal nanoclusters (NCs) are scarce. This has hampered the development of this unique class of nanomaterials. Here, a general protocol is reported for the synthesis of high-quality metal NCs protected by a variety of organic ligands (e.g., selenolate, thiolate, and phosphine) based on a miscible-solvent-assisted phase transfer between water and organic solution. This method is demonstrated to be facile, rapid (≤3 h), scalable (gram-scale), and versatile. The size of the selenolated and thiolated Au NCs can be tuned from Au₁₀ to Au₆₁ by simply varying the miscible solvent in proportions and types. The advantages of this method, such as quick phase separation and no need for purification treatment, enable real-time monitoring of metal NC growth within the NaBH₄ reduction system. The results show that the size of Au NCs gradually increases with increasing valence electron count by a stepwise 2x e^- hopping mechanism (x = 0-5), i.e., 0 e^- → 2 e^- → 4 e^- → 8 e^- → 18 e^- → 22 e^- → 32 e^- .

Confining Sub-Nanometer Pt Clusters in Hollow Mesoporous Carbon Spheres for Boosting Hydrogen Evolution Activity

Electrochemical water splitting is considered as a promising approach to produce clean and sustainable hydrogen fuel. As a new class of nanomaterials with high ratio of surface atoms and tunable composition and electronic structure, metal clusters are promising candidates as catalysts. Here, a new strategy is demonstrated to synthesize active and stable Pt-based electrocatalysts for hydrogen evolution by confining Pt clusters in hollow mesoporous carbon spheres (Pt₅ /HMCS). Such a structure would effectively stabilize the Pt clusters during the ligand removal process, leading to remarkable electrocatalytic performance for hydrogen production in both acidic and alkaline solutions. Particularly, the optimal Pt₅ /HMCS electrocatalyst exhibits 12 times the mass activity of Pt in commercial Pt/C catalyst with similar Pt loading. This study exemplifies a simple yet effective approach to improve the cost effectiveness of precious-metal-based catalysts with stabilized metal clusters.

Gold Nanoclusters as Electrocatalysts for Energy Conversion

Gold nanoclusters (Aun NCs) exhibit a size-specific electronic structure unlike bulk gold and can therefore be used as catalysts in various reactions. Ligand-protected Aun NCs can be synthesized with atomic precision, and the geometric structures of many Aun NCs have been determined by single-crystal X-ray diffraction analysis. In addition, Aun NCs can be doped with various types of elements. Clarification of the effects of changes to the chemical composition, geometric structure, and associated electronic state on catalytic activity would enable a deep understanding of the active sites and mechanisms in catalytic reactions as well as key factors for high activation. Furthermore, it may be possible to synthesize Aun NCs with properties that surpass those of conventional catalysts using the obtained design guidelines. With these expectations, catalyst research using Aun NCs as a model catalyst has been actively conducted in recent years. This review focuses on the application of Aun NCs as an electrocatalyst and outlines recent research progress.

Excitonic Au4Ru2(PPh3)2(SC2H4Ph)8 cluster for light-driven dinitrogen fixation

The surface plasmon resonance of metal nanoparticles has been widely used to improve photochemical transformations by plasmon-induced charge transfer. However, it remains elusive for the molecular-like metal clusters with non-metallic or excitonic behavior to enable light harvesting including electron/hole pair production and separation. Here we report a paradigm for solar energy conversion on an atomically precise Au₄Ru₂ cluster supported on TiO₂ with oxygen vacancies, in which the electron–hole pairs can be directly generated from the excited Au₄Ru₂ cluster and the TiO₂ support, and the photogenerated electrons can transfer to the Ru atoms. Importantly, the Ru atoms in the Au₄Ru₂ cluster are capable of injecting the electrons into adsorbed N₂ to activate N₂ molecules. The cooperative effect in the supported Au₄Ru₂ catalyst efficiently boosts the photocatalytic activity for N₂ fixation in comparison with homogold (Au_n) clusters.

A molecular-like Au₄Ru₂ cluster supported on TiO₂ with oxygen vacancies enables light harvesting to drive the fixation of N₂.

Photo/electrocatalysis and photosensitization using metal nanoclusters for green energy and medical applications

Owing to the rapidly increasing demand for sustainable technologies in fields such as energy, environmental science, and medicine, nanomaterial-based photo/electrocatalysis has received increasing attention. Recently, synthetic innovations have allowed the fabrication of atomically precise metal nanoclusters (NCs). These NCs show potential for green energy and medical applications. The present article primarily focuses on evaluation of the recent developments in the photo/electrocatalytic and photosensitizing characteristics of metal and alloy NCs. The review comprises two sections: (i) photo/electrocatalysis for green energy and (ii) photosensitization for biomedical therapy applications. Finally, the challenges associated with the use of metal NCs are presented on the basis of current developments.

Ultrastable hydrido gold nanoclusters with the protection of phosphines

Two phosphine-protected gold nanoclusters with an unprecedented hetero superatomic Au₂₀ core have been isolated. The presence of hydrides is evidenced by mass spectrometry and NMR spectroscopy.

The positional isomerism in bimetal nanoclusters

Enriching the variety of isomerism in the nanocluster field is exciting but challenging.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

Engineering ultrasmall metal nanoclusters for photocatalytic and electrocatalytic applications

In view of many of the fundamental properties of ultrasmall noble metal nanoclusters progressively being uncovered, it has become increasingly clear that this class of materials has enormous potential for photocatalytic and electrocatalytic applications due to their unique electronic and optical properties. In this Minireview, we highlight the key electronic and optical properties of metal nanoclusters which are essential to photocatalysis and electrocatalysis. We further use these properties as the basis for our discussion to map out directions or principles for the rational design of high performance photocatalysts and electrocatalysts, highlighting several successful attempts along this direction.

Elucidating ligand effects in thiolate-protected metal clusters using Au24Pt(TBBT)18 as a model cluster

2-Phenylethanethiolate (PET) and 4-tert-butylbenzenethiolate (TBBT) are the most frequently used ligands in the study of thiolate (SR)-protected metal clusters. However, the effect of difference in the functional group between these ligands on the fundamental properties of the clusters has not been clarified. We synthesized [Au24Pt(TBBT)18]0, which has the same number of metal atoms, number of ligands, and framework structure as [Au24Pt(PET)18]0, by replacing ligands of [Au24Pt(PET)18]0 with TBBT. It was found that this ligand exchange is reversible unlike the case of other metal-core clusters. A comparison of the geometrical/electronic structure and stability of the clusters between [Au24Pt(PET)18]0 and [Au24Pt(TBBT)18]0 revealed three things with regard to the effect of ligand change from PET to TBBT on [Au24Pt(SR)18]0: (1) the induction of metal-core contraction and Au-S bond elongation, (2) no substantial effect on the HOMO-LUMO gap but a clear difference in optical absorption in the visible region, and (3) the decrease of stabilities against degradation in solution and under laser irradiation. By using these two clusters as model clusters, it is expected that the effects of the structural difference of ligand functional-groups on the physical properties and functions of clusters, such as catalytic ability and photoluminescence, would be clarified.

Gram-Scale Preparation of Stable Hydride M@Cu24 (M = Au/Cu) Nanoclusters

The instability of phosphine ligated copper hydride nanoclusters (CuH NCs) has largely limited their application in areas such as H₂ storage, CO₂ reduction, etc. In this work, the stability of CuH NCs was remarkably enhanced by improving their antioxidant capacity through two different approaches: (i) metal doping and (ii) ligand modification. Three NCs, AuCu₂₄H₂₂(PPh₃)₁₂, Cu₂₅H₂₂((p-FPh)₃P)₁₂, and AuCu₂₄H₂₂((p-FPh)₃P)₁₂, were controllably synthesized, and their structures were determined by single-crystal X-ray diffraction. The compositions of these NCs were further confirmed by electrospray ionization mass spectrometry and nuclear magnetic resonance. More importantly, we achieved gram-level production of M@Cu₂₄ (M = Cu/Au) NCs protected by electron-withdrawing ligands (p-FPh)₃P, which in turn proved their superior stability; such a large-scale preparation laid the foundation for future explorations of copper-rich NCs. This work hopes to shed light on large-scale generation of ultrastable Cu-based NCs.

An Au22(L8)6 nanocluster with in situ uncoordinated Au as a highly active catalyst for O2 activation and CO oxidation

Ligand-capped gold nanoclusters with atomic precision have attracted great interest as a new type of nanocatalyst to elucidate mechanisms and establish structure-reactivity correlations. In most cases, however, the catalytic activity of fully protected gold nanoclusters is severely hindered due to the blocking effects of the ligands. Alternatively, partially protected gold nanoclusters with the creation of in situ coordination unsaturated (cus) Au are highly promising for nanocatalysis. In this study, via density functional theory (DFT) calculations, we investigated the reactivity of a diphosphine-protected Au22(L8)6 nanocluster using oxygen activation and CO oxidation as the testing probes. The results showed that the cus Au at the interface shows strong adsorption and activation of oxygen, promoting the dissociation of two O2 molecules into fully oxidized Au22(L8)6O4 nanoclusters with a moderate activation barrier (0.6-0.7 eV). The adsorption of additional O2 prefers molecular adsorption and locates at the terminal Au11 unit around the Au-P framework. Furthermore, our results indicate that the Au22(L8)6 cluster shows very high activity and a low energy barrier (0.51 eV) for CO oxidation. The facile O2 activation and CO oxidation over the Au22(L8)6 nanocatalyst will aid the rational design of partially protected metal nanoclusters with coordination unsaturated metal centers in oxidation or other catalytic reactions for important practical applications.

Rational construction of a library of M29 nanoclusters from monometallic to tetrametallic

Exploring intermetallic synergy has allowed a series of alloy nanoparticles with prominent chemical-physical properties to be produced. However, precise alloying based on a maintained template has long been a challenging pursuit, and little has been achieved for manipulation at the atomic level. Here, a nanosystem based on M₂₉(S-Adm)₁₈(PPh₃)₄ (where S-Adm is the adamantane mercaptan and M is Ag/Cu/Au/Pt/Pd) has been established, which leads to the atomically precise operation on each site in this M₂₉ template. Specifically, a library of 21 species of nanoclusters ranging from monometallic to tetrametallic constitutions has been successfully prepared step by step with in situ synthesis, target metal-exchange, and forced metal-exchange methods. More importantly, owing to the monodispersity of each nanocluster in this M₂₉ library, the synergetic effects on the optical properties and stability have been mapped out. This nanocluster methodology not only provides fundamental principles to produce alloy nanoclusters with multimetallic compositions and monodispersed dopants but also provides an intriguing nanomodel that enables us to grasp the intermetallic synergy at the atomic level.

Pt-Based Nanocrystal for Electrocatalytic Oxygen Reduction

Currently, Pt-based electrocatalysts are adopted in the practical proton exchange membrane fuel cell (PEMFC), which converts the energy stored in hydrogen and oxygen into electrical power. However, the broad implementation of the PEMFC, like replacing the internal combustion engine in the present automobile fleet, sets a requirement for less Pt loading compared to current devices. In principle, the requirement needs the Pt-based catalyst to be more active and stable. Two main strategies, engineering of the electronic (d-band) structure (including controlling surface facet, tuning surface composition, and engineering surface strain) and optimizing the reactant adsorption sites are discussed and categorized based on the fundamental working principle. In addition, general routes for improving the electrochemical surface area, which improves activity normalized by the unit mass of precious group metal/platinum group metal, and stability of the electrocatalyst are also discussed. Furthermore, the recent progress of full fuel cell tests of novel electrocatalysts is summarized. It is suggested that a better understanding of the reactant/intermediate adsorption, electron transfer, and desorption occurring at the electrolyte-electrode interface is necessary to fully comprehend these electrified surface reactions, and standardized membrane electrode assembly (MEA) testing protocols should be practiced, and data with full parameters detailed, for reliable evaluation of catalyst functions in devices.

Design and site-directed compartmentalization of gold nanoclusters within the intrasubunit interfaces of ferritin nanocage

BACKGROUND

Protein nanocages have emerged as popular nanocarriers for either drug delivery or biotemplates for the preparation of nanomaterials. However, only three interfaces, namely exterior surface, intersubunit and inner cavity, have been used as reaction sites for the above purposes with all known protein nanocages. On the other hand, how to control the site of Au NCs formed within a targeted protein template while maintaining the functionality of protein itself remains challenging.

RESULTS

In this work, inspired by compartmentalization in living systems, we firstly come up with the conception of "intrasubunit interfaces", located within subunit of protein nanocage. We built a new, specific compartment for fabrication of gold nanoclusters by genetic modification of the inherent ferroxidase center located within four-α-helix bundle of each ferritin subunit. This newly built compartment not only realizes the site-directed synthesis of gold nanoclusters but also has no effect on the functionality of ferritin itself such as encapsulation by its inner cavity. These redesigned composites can be further applied as fluorescent imaging agent and carriers for preparation of hybrid nanomaterials.

CONCLUSIONS

The designing strategy of intrasubunit interfaces opens a new way for future applications of cage-like proteins.

Alternating Array Stacking of Ag26 Au and Ag24 Au Nanoclusters

An assembly strategy for metal nanoclusters using electrostatic interactions with weak interactions, such as C-H⋅⋅⋅π and π⋅⋅⋅π interactions in which cationic [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ and anionic [Ag₂₄ Au(2-EBT)₁₈ ]^- nanoclusters gather and assemble in an unusual alternating array stacking structure is presented. [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- is a new compound type, a double nanocluster ion compound (DNIC). A single nanocluster ion compound (SNIC) [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- was also synthesized, having a k-vector-differential crystallographic arrangement. [PPh₄ ]⁺ [Ag₂₄ Au(2,4-DMBT)₁₈ ]^- adopts a different assembly mode from both [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- and [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- . Thus, the striking packing differences of [Ag₂₆ Au(2-EBT)₁₈ (PPh₃ )₆ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- , [PPh₄ ]⁺ [Ag₂₄ Au(2-EBT)₁₈ ]^- and the existing [PPh₄ ]⁺ [Ag₂₄ Au(2,4-DMBT)₁₈ ]^- from each other indicate the notable influence of ligands and counterions on the self-assembly of nanoclusters.