Photochemical tuning of dynamic defects for high-performance atomically dispersed catalysts.

Developing active and stable atomically dispersed catalysts is challenging because of weak non-specific interactions between catalytically active metal atoms and supports. Here we demonstrate a general method for synthesizing atomically dispersed catalysts via photochemical defect tuning for controlling oxygen-vacancy dynamics, which can induce specific metal-support interactions. The developed synthesis method offers metal-dynamically stabilized atomic catalysts, and it can be applied to reducible metal oxides, including TiO2, ZnO and CeO2, containing various catalytically active transition metals, including Pt, Ir and Cu. The optimized Pt-DSA/TiO2 shows unprecedentedly high photocatalytic hydrogen evolution activity, producing 164 mmol g-1 h-1 with a turnover frequency of 1.27 s-1. Furthermore, it generates 42.2 mmol gsub-1 of hydrogen via a non-recyclable-plastic-photoreforming process, achieving a total conversion of 98%; this offers a promising solution for mitigating plastic waste and simultaneously producing valuable energy sources.

Cation Exchange in Colloidal Transition Metal Nitride Nanocrystals.

Transition metal nitride (TMN)-based nanostructures have emerged as promising materials for diverse applications in electronics, photonics, energy storage, and catalysis due to their highly desirable physicochemical properties. However, synthesizing TMN-based nanostructures with designed compositions and morphologies poses challenges, especially in the solution phase. The cation exchange reaction (CER) stands out as a versatile postsynthetic strategy for preparing nanostructures that are otherwise inaccessible through direct synthesis. Nevertheless, exploration of the CER in TMNs lags behind that in metal chalcogenides and metal phosphides. Here, we demonstrate cation exchange in colloidal metal nitride nanocrystals, employing Cu3N nanocrystals as starting materials to synthesize Ni4N and CoN nanocrystals. By controlling the reaction conditions, Cu3N@Ni4N and Cu3N@CoN core@shell heterostructures with tunable compositions can also be obtained. The Ni4N and CoN nanocrystals are evaluated as catalysts for the electrochemical oxygen evolution reaction (OER). Remarkably, CoN nanocrystals demonstrate superior OER performance with a low overpotential of 286 mV at 10 mA·cm-2, a small Tafel slope of 89 mV·dec-1, and long-term stability. Our CER approach in colloidal TMNs offers a new strategy for preparing other metal nitride nanocrystals and their heterostructures, paving the way for prospective applications.

Synthesis, Assembly, and Applications of Magic-Sized Semiconductor (CdSe)13 Cluster.

ConspectusAtomically precise metal chalcogenide clusters (MCCs) are model molecular compounds of scientifically and technologically important semiconductor nanocrystals, which are known as quantum dots (QDs). The significantly high ambient stability of MCCs of particular sizes, as compared to that of slightly smaller or larger sizes, made them be termed "magic-sized clusters" (MSCs). In other words, MSCs with specific sizes between sizes of precursors (typically, metal-ligand complexes) and nanocrystals (typically, QDs) appear sequentially during the colloidal synthesis of nanocrystals, while the other cluster species decompose to precursor monomers or are consumed during the growth of the nanocrystals. Unlike nanocrystals with an ambiguous atomic-level structure and a substantial size distribution, MSCs possess atomically monodisperse size, composition, and distinct atomic arrangement. Chemical synthesis and exploration of properties of MSCs are of great significance since they help systematically understand the evolution of fundamental properties as well as build structure-activity relationships at distinct molecular levels. Furthermore, MSCs are anticipated to offer atomic-level insights into the growth mechanism of the semiconductor nanocrystals, which is highly desirable in the design of advanced materials with new functions. In this Account, we cover our recent efforts in the advancement of one of the most important stoichiometric CdSe MSCs, (CdSe)13. In particular, we present its molecular structure derived from a single crystal X-ray crystallographic study of the closest MSC, Cd14Se13. The crystal structure of MSC enables not only the understanding of the electronic structure and prediction of the potential sites for heteroatom dopants (e.g., Mn2+ and Co2+) but also the identification of favorable synthetic conditions for the selective synthesis of desired MSCs. Next, we focus on enhancing the photoluminescence quantum yield and stability of Mn2+ doped (CdSe)13 MSCs through their self-assembly, which is facilitated by the rigid diamines. In addition, we show how atomic-level synergistic effects and functional groups of the assemblies of alloy MSCs can be utilized for a highly enhanced catalytic CO2 fixation with epoxides. Benefiting from the intermediate stability, the MSCs are explored as single-source precursors to low-dimensional nanostructures, such as nanoribbons and nanoplatelets, through the controlled transformation. Distinct differences in the outcome of the solid-state and colloidal-state conversion of MSCs suggest the need for careful consideration of the phase and reactivity of MSCs as well as the type of dopant to achieve novel structured multicomponent semiconductors. Finally, we summarize the Account and provide future perspectives on the fundamental and applied scientific research of MSCs.

Body-Centered-Cubic-Kernelled Ag15Cu6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO2 Electroreduction.

While atomically monodisperse nanostructured materials are highly desirable to unravel the size- and structure-catalysis relationships, their controlled synthesis and the atomic-level structure determination pose challenges. Particularly, copper-containing atomically precise alloy nanoclusters are potential catalyst candidates for the electrochemical CO2 reduction reaction (eCO2RR) due to high abundance and tunable catalytic activity of copper. Herein, we report the synthesis and total structure of an alkynyl-protected 21-atom AgCu alloy nanocluster [Ag15Cu6(C≡CR)18(DPPE)2]-, denoted as Ag15Cu6 (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene; DPPE: 1,2-bis(diphenylphosphino)ethane). The single-crystal X-ray diffraction reveals that Ag15Cu6 consists of an Ag11Cu4 metal core exhibiting a body-centered cubic (bcc) structure, which is capped by 2 Cu atoms, 2 Ag2DPPE motifs, and 18 alkynyl ligands. Interestingly, the Ag15Cu6 cluster exhibits excellent catalytic activity for eCO2RR with a CO faradaic efficiency (FECO) of 91.3% at -0.81 V (vs the reversible hydrogen electrode, RHE), which is much higher than that (FECO: 48.5% at -0.89 V vs RHE) of Ag9Cu6 with bcc structure. Furthermore, Ag15Cu6 shows superior stability with no significant decay in the current density and FECO during a long-term operation of 145 h. Density functional theory calculations reveal that the de-ligated Ag15Cu6 cluster can expose more space at the pair of AgCu dual metals as the efficient active sites for CO formation.

Copper Doping Boosts Electrocatalytic CO2 Reduction of Atomically Precise Gold Nanoclusters.

Unraveling the atomistic synergistic effects of nanoalloys on the electrocatalytic CO2 reduction reaction (eCO2RR), especially in the presence of copper, is of paramount importance. However, this endeavor encounters significant challenges due to the lack of the crystallographically determined atomic-level structure of appropriate monometallic and bimetallic analogues. Herein, we report a one-pot synthesis and structure characterization of a AuCu nanoalloy cluster catalyst, [Au15Cu4(DPPM)6Cl4(C≡CR)1]2+ (denoted as Au15Cu4). Single-crystal X-ray diffraction analysis reveals that Au15Cu4 comprises two interpenetrating incomplete, centered icosahedra (Au9Cu2 and Au8Cu3) and is protected by six DPPM, four halide, and one alkynyl ligand. The Au15Cu4 cluster and its closest monometal structural analogue, [Au18(DPPM)6Br4]2+ (denoted as Au18), as model systems, enable the elucidation of the atomistic synergistic effects of Au and Cu on eCO2RR. The results reveal that Au15Cu4 is an excellent eCO2RR catalyst in a gas diffusion electrode-based membrane electrode assembly (MEA) cell, exhibiting a high CO Faradaic efficiency (FECO) of >90%, and this efficiency is substantially higher than that of the undoped Au18 (FECO: 60% at -3.75 V). Au15Cu4 exhibits an industrial-level CO partial current density of up to -413 mA/cm2 at -3.75 V with the gas CO2-fed MEA, which is 2-fold higher than that of Au18. The density functional theory (DFT) calculations demonstrate that the synergistic effects are induced by Cu doping, where the exposed pair of AuCu dual sites was suggested for launching the eCO2RR process. Besides, DFT simulations reveal that these special dual sites synergistically coordinate a moderate shift in the d-state, thus enhancing its overall catalytic performance.

Synergistic Interactions of Neighboring Platinum and Iron Atoms Enhance Reverse Water-Gas Shift Reaction Performance.

The limitations of conventional strategies in finely controlling the composition and structure demand new promotional effects for upgrading the reverse water-gas shift (RWGS) catalysts for enhanced fuel production. We report the design and synthesis of a hetero-dual-site catalyst for boosting RWGS performance by controllably loading Fe atoms at the neighboring Pt atom on the surface of commercial CeO2. The Fe-Pt/CeO2 exhibits a remarkably high catalytic performance (TOFPt: 43,519 h-1) for CO2 to CO conversion with ∼100% CO selectivity at a relatively low temperature of 350 °C. Furthermore, the catalyst retains over 80% activity after 200 h of continuous operation. The experimental and computational investigations reveal a "two-way synergistic effect", where Fe atoms can not only serve as promotors to alter the charge density of Pt atoms but also be activated by the excess active hydrogen species generated by Pt atoms, enhancing catalytic activity and stability.

Facet-Defined Strain-Free Spinel Oxide for Oxygen Reduction.

Exposing facet and surface strain are critical factors affecting catalytic performance but unraveling the composition-dependent activity on specific facets under strain-controlled environment is still challenging due to the synthetic difficulties. Herein, we achieved a (001) facet-defined Co-Mn spinel oxide surface with different surface compositions using epitaxial growth on Co3O4 nanocube template. We adopted composition gradient synthesis to relieve the strain layer by layer, minimizing the surface strain effect on catalytic activity. In this system, experimental and calculational analyses of model oxygen reduction reaction (ORR) activity reveals a volcano-like trend with Mn/Co ratios because of an adequate charge transfer from octahedral-Mn to neighboring Co. Co0.5Mn0.5 as an optimized Mn/Co ratio exhibits both outstanding ORR activity (0.894 V vs RHE in 1 M KOH) and stability (2% activity loss against chronoamperometry). By controlling facet and strain, this study provides a well-defined platform for investigating composition-structure-activity relationships in electrocatalytic processes.

Alkynyl-Protected Chiral Bimetallic Ag22 Cu7 Superatom with Multiple Chirality Origins.

Understanding the origin of chirality in the nanostructured materials is essential for chiroptical and catalytic applications. Here we report a chiral AgCu superatomic cluster, [Ag22 Cu7 (C≡CR)16 (PPh3 )5 Cl6 ](PPh4 ), Ag22 Cu7 , protected by an achiral alkynyl ligand (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene). Its crystal structure comprises a rare interpenetrating biicosahedral Ag17 Cu2 core, which is stabilized by four different types of motifs: one Cu(C≡CR)2 , four -C≡CR, two chlorides and one helical Ag5 Cu4 (C≡CR)10 (PPh3 )5 Cl4 . Structural analysis reveals that Ag22 Cu7 exhibits multiple chirality origins, including the metal core, the metal-ligand interface and the ligand layer. Furthermore, the circular dichroism spectra of R/S-Ag22 Cu7 are obtained by employing appropriate chiral molecules as optical enrichment agents. DFT calculations show that Ag22 Cu7 is an eight-electron superatom, confirm that the cluster is chirally active, and help to analyze the origins of the circular dichroism.

Single-Atom Rh on High-Index CeO2 Facet for Highly Enhanced Catalytic CO Oxidation.

Reducible oxide-supported noble metal nanoparticles exhibit high activity in catalyzing many important oxidation reactions. However, atom migration under harsh reaction conditions leads to deactivation of the catalyst. Meanwhile, single-atom catalysts demonstrate enhanced stability, but often suffer from poor catalytic activity owing to the ionized surface states. In this work, we simultaneously address the poor activity and stability issues by synthesizing highly active and durable rhodium (Rh) single-atom catalysts through a "wrap-bake-peel" process. The pre-coated SiO2 layer during synthesis of catalyst plays a crucial role in not only protecting CeO2 support against sintering, but also donating electron to weaken the Ce-O bond, producing highly loaded Rh single atoms on the CeO2 support exposed with high-index {210} facets. Benefiting from the unique electronic structure of CeO2 {210} facets, more oxygen vacancies are generated along with the deposition of more electropositive Rh single atoms, leading to remarkably improved catalytic performance in CO oxidation.

Highly luminescent and catalytically active suprastructures of magic-sized semiconductor nanoclusters.

Metal chalcogenide magic-sized nanoclusters have shown intriguing photophysical and chemical properties, yet ambient instability has hampered their extensive applications. Here we explore the periodic assembly of these nanoscale building blocks through organic linkers to overcome such limitations and further boost their properties. We designed a diamine-based heat-up self-assembly process to assemble Mn2+:(CdSe)13 and Mn2+:(ZnSe)13 magic-sized nanoclusters into three- and two-dimensional suprastructures, respectively, obtaining enhanced stability and solid-state photoluminescence quantum yields (from <1% for monoamine-based systems to ~72% for diamine-based suprastructures). We also exploited the atomic-level miscibility of Cd and Zn to synthesize Mn2+:(Cd1-xZnxSe)13 alloy suprastructures with tunable metal synergy: Mn2+:(Cd0.5Zn0.5Se)13 suprastructures demonstrated high catalytic activity (turnover number, 17,964 per cluster in 6 h; turnover frequency, 2,994 per cluster per hour) for converting CO2 to organic cyclic carbonates under mild reaction conditions. The enhanced stability, photoluminescence and catalytic activity through combined cluster-assembly and metal synergy advance the usability of inorganic semiconductor nanoclusters.

[Pt2Cu34(PET)22Cl4]2-: An Atomically Precise, 10-Electron PtCu Bimetal Nanocluster with a Direct Pt-Pt Bond.

Heteroatom-doped metal nanoclusters (NCs) are highly desirable to gain fundamental insights into the effect of doping on the electronic structure and catalytic properties. Unfortunately, their controlled synthesis is highly challenging when the metal atomic sizes are largely different (e.g., Cu and Pt). Here, we design a metal-exchange strategy that enables simultaneous doping and resizing of NCs. Specifically, [Pt2Cu34(PET)22Cl4]2- NC, the first example of a Pt-doped Cu NC, is synthesized by utilizing the unique reactivity of [Cu32(PET)24Cl2H8]2- NC with Pt4+ ions. The single-crystal X-ray structure reveals that two directly bonded Pt atoms occupy the two centers of an unusually interpenetrating, incomplete biicosahedron core (Pt2Cu18), which is stabilized by a Cu16(PET)22Cl4 shell. The molecular structure and composition of the NC are validated by combined experimental and theoretical results. Electronic structure calculations, using the density functional theory, show that the Pt2Cu34 NC is a 10-electron superatom. The computed absorption spectrum matches well with the measured data and allows for assignment of the absorption peaks. The calculations also rationalize energetics for ligand exchange observed in the mass spectrometry data. The synergistic effects induced by Pt doping are found to enhance the catalytic activity of Cu NCs by ∼300-fold in silane to silanol conversion under mild conditions. Furthermore, our synthetic strategy has potential to produce Ni-, Pd-, and Au-doped Cu NCs, which will open new avenues to uncover their molecular structures and catalytic properties.

Highly Fluorescent Gold Cluster Assembly.

The photoluminescence (PL) of metal nanoclusters (NCs), originating from their molecule-like electronic structure, is one of the most intriguing properties of NCs. Although various strategies such as tailoring the size, structure, and chemical environment of NCs have shown to improve the PL, their quantum yields (QYs) are still lagging far behind those of conventional luminescent materials, including quantum dots and organic fluorophores. Herein, we report the synthesis of highly luminescent gold cluster assembly (GCA) from Zn2+-ion-mediated assembly of Au4(SRCOO-)4 clusters using mercaptocarboxylic acid as a protective ligand and reductant as well as a growth suppressor. The synergetic combination of unique aurophilic interactions among Au4 clusters and the rigidified chemical environment induced by metal ion chelation through carboxylate groups is responsible for the ultrabright greenish-blue fluorescence with a QY up to 90%. Furthermore, the unique flexibility of dis/reassembly and the aggregation-dependent strong fluorescence of GCA offer a great potential for applications in biodegradable and trackable drug delivery systems.

Magic-Sized Stoichiometric II-VI Nanoclusters.

Metal chalcogenide nanomaterials have gained widespread interest in the past two decades for their potential optoelectronic, energy, and catalytic applications. The colloidal growth of various forms of these materials, such as nanowires, platelets, and lamellar assemblies, proceeds through certain thermodynamically stable, ultrasmall (<2 nm) intermediates called magic-sized nanoclusters (MSCs). Due to quantum confinement and its resultant intriguing properties, isolation or direct synthesis of MSCs and their structure characterization, which is very much challenging, are current topics of fundamental and applied scientific research. By comprehensive understanding of the structure-activity relationships in MSCs, the nucleation and growth processes can be manipulated, resulting in the synthesis of novel metal chalcogenide materials for various applications. This review focuses on recent advances in the chemical synthesis, characterization, and theoretical calculations of CdSe and its related II-VI nanoclusters. It highlights the studies of photophysical and magneto-optical properties as well as heteroatom doping of MSCs followed by their chemical transformation to high-dimensional nanostructures. At the end of the review, future directions and possible ways to overcome the challenges in the research of semiconductor MSCs are also presented.

[Ag9(1,2-BDT)6]3-: How Square-Pyramidal Building Blocks Self-Assemble into the Smallest Silver Nanocluster.

The emerging promise of few-atom metal catalysts has driven the need for developing metal nanoclusters (NCs) with ultrasmall core size. However, the preparation of metal NCs with single-digit metallic atoms and atomic precision is a major challenge for materials chemists, particularly for Ag, where the structure of such NCs remains unknown. In this study, we developed a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized Ag NC to date: [Ag9(1,2-BDT)6]3- (1,2-BDT = 1,2-benzenedithiolate). The NC's crystal structure reveals the self-assembly of two Ag square pyramids through preferential pyramidal vertex sharing of a single metallic Ag atom, while all other Ag atoms are incorporated in a motif with thiolate ligands, resulting in an elongated body-centered Ag9 skeleton. Steric hindrance and arrangement of the dithiolated ligands on the surface favor the formation of an anisotropic shape. Time-dependent density functional theory based calculations reproduce the experimental optical absorption features and identify the molecular orbitals responsible for the electronic transitions. Our findings will open new avenues for the design of novel single-digit metal NCs with directional self-assembled building blocks.

High photoluminescence from self-assembled Ag2Cl2(dppe)2 clusters through metallophilic interactions.

Ligand protected metal nanoclusters (NCs) are an emerging class of functional materials with intriguing photophysical and chemical properties. The size and molecular structure play an important role in endowing NCs with characteristic optical and electronic properties. Modulation of these properties through the chemical reactivity of NCs is largely unexplored. Here, we report on the synthesis of self-assembled Ag2Cl2(dppe)2 clusters through the ligand-exchange-induced transformation of [Pt2Ag23Cl7(PPh3)10] NCs [(dppe): 1,2-bis(diphenylphosphino)ethane; (PPh3): triphenylphosphine]. The single crystal x-ray structure reveals that two Ag atoms are bridged by one dppe and two Cl ligands, forming a Ag2Cl2(dppe) cluster, which is subsequently self-assembled through dppe ligands to form [Ag2Cl2(dppe)2]n. Importantly, the Ag2Cl2(dppe)2 cluster assembly exhibits high photoluminescence quantum yield: ∼18%, which is attributed to the metallophilic interactions and rigidification of the ligand shell. We hope that this work will motivate the exploitation of the chemical reactivity of NCs as a new path to attain cluster assemblies endowed with enhanced photophysical properties.

Ag44 (EBT)26 (TPP)4 Nanoclusters With Tailored Molecular and Electronic Structure.

Although atomically precise metalloid nanoclusters (NCs) of identical size with distinctly different molecular structures are highly desirable to understand the structural effects on the optical and photophysical properties, their synthesis remains highly challenging. Herein, we employed phosphine and thiol capping ligands featuring appropriate steric effects and synthesized a charge-neutral Ag NC with the formula Ag44 (EBT)26 (TPP)4 (EBT: 2-ethylbenzenethiolate; TPP: triphenylphosphine). The single-crystal X-ray structure reveals that this NC has a hollow metal core of Ag12 @Ag20 and a metal-ligand shell of Ag12 (EBT)26 (TPP)4 . The presence of mixed ligands and long V-shaped metal-ligand motifs on this NC has resulted in an enhancement of the NIR-II photoluminescence quantum yield by >25-fold compared to an all-thiolate-stabilized anionic [Ag44 (SR)30 ]4- NC (SR: thiolate). Time-dependent density-functional calculations show that our Ag44 NC is an 18-electron superatom with a modulated electronic structure as compared to the [Ag44 (SR)30 ]4- anion, significantly influencing its optical properties.

[Cu32(PET)24H8Cl2](PPh4)2: A Copper Hydride Nanocluster with a Bisquare Antiprismatic Core.

Atomically precise coinage metal (Au, Ag, and Cu) nanoclusters (NCs) have been the subject of immense interest for their intriguing structural, photophysical, and catalytic properties. However, the synthesis of Cu NCs is highly challenging because of low reduction potential and high reactivity of copper, demonstrating the need for new synthetic methods using appropriate ligand combinations. By designing a diamine-assisted synthetic strategy, here we report the synthesis and total structure characterization of a box-like dianionic Cu NC [Cu32(PET)24H8Cl2](PPh4)2 coprotected by 2-phenylethanethiolate (PET), hydride, and chloride ligands. Its crystal structure comprises a rare bisquare antiprismatic Cu14H8 core, assembled by two square antiprisms by edge sharing, followed by hydride binding. The rod-shaped Cu14H8 core is clamped by two complex Cu7(PET)11Cl and two simple Cu2PET metal ligand frameworks, constructing the complete structure of Cu32 NC. The presence, number, and location of hydrides are established by combined experimental and density functional theory results. The electronic structure calculations show the cluster as a zero-free-electron system, reproduce well the measured optical absorption spectrum, and explain the main absorption features. Furthermore, the Cu32 cluster is found to be a highly active homogeneous catalyst for C-N bond formation in aniline carbonylation reactions at room temperature. We hope that new findings in this work will stimulate and expand the research on Cu and other active metal NCs.

Direct Synthesis of Intermetallic Platinum-Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis.

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)3]2+ cation (bpy = 2,2'-bipyridine) and [PtCl6]2- anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.

Cd12Ag32(SePh)36: Non-Noble Metal Doped Silver Nanoclusters.

While there are numerous recent reports on doping of a ligand-protected noble metal nanocluster (e.g., Au and Ag) with another noble metal, non-noble metal (e.g., Cd) doping remains challenging. Here, we design a phosphine-assisted synthetic strategy and synthesize a Cd doped Ag nanocluster, Cd12Ag32(SePh)36 (SePh: selenophenolate), which exhibits characteristic UV-vis absorption features and rare near-infrared (NIR) photoluminescence at ∼1020 nm. The X-ray single crystal structure reveals an asymmetric two-shell Ag4@Ag24 metal kernel protected by four nonplanar Cd3Ag(SePh)9 metal-ligand frameworks. Furthermore, the electronic structure analysis shows that the cluster is a 20-electron "superatom" and density functional theory predicts that its chiral optical response is comparable to the well-known Au38(SR)24 cluster. Our synthetic approach will pave a new path for introducing other non-noble metals into noble metal nanoclusters for exploring their effect on optical and chemical properties.

Molecular-Level Understanding of Continuous Growth from Iron-Oxo Clusters to Iron Oxide Nanoparticles.

The formation of inorganic nanoparticles has been understood based on the classical crystallization theory described by a burst of nucleation, where surface energy is known to play a critical role, and a diffusion-controlled growth process. However, this nucleation and growth model may not be universally applicable to the entire nanoparticle systems because different precursors and surface ligands are used during their synthesis. Their intrinsic chemical reactivity can lead to a formation pathway that deviates from a classical nucleation and growth model. The formation of metal oxide nanoparticles is one such case because of several distinct chemical aspects during their synthesis. Typical carboxylate surface ligands, which are often employed in the synthesis of oxide nanoparticles, tend to continuously remain on the surface of the nanoparticles throughout the growth process. They can also act as an oxygen source during the growth of metal oxide nanoparticles. Carboxylates are prone to chemical reactions with different chemical species in the synthesis such as alcohol or amine. Such reactions can frequently leave reactive hydroxyl groups on the surface. Herein, we track the entire growth process of iron oxide nanoparticles synthesized from conventional iron precursors, iron-oleate complexes, with strongly chelating carboxylate moieties. Mass spectrometry studies reveal that the iron-oleate precursor is a cluster comprising a tri-iron-oxo core and carboxylate ligands rather than a mononuclear complex. A combinatorial analysis shows that the entire growth, regulated by organic reactions of chelating ligands, is continuous without a discrete nucleation step.