Symmetry Breaking Enhancing the Activity of Electrocatalytic CO2 Reduction on an Icosahedron-Kernel Cluster by Cu Atoms Regulation.

Recently, CO2 hydrogenation had a new breakthrough resulting from the design of catalysts to effectively activate linear CO2 with symmetry-breaking sites. However, understanding the relationship between symmetry-breaking sites and catalytic activity at the atomic level is still a great challenge. In this study, a set of gold-copper alloy Au13 Cux (x=0-4) nanoclusters were used as research objects to show the symmetry-controlled breaking structure on the surface of nanoclusters with the help of manipulability of the Cu atoms. Among them, Au13 Cu3 nanocluster displays the highest degree of symmetry-breaking on its crystal structure compared with the other nanoclusters in the family. Where the three copper atoms occupying the surface of the icosahedral kernel unevenly with one copper atom is coordinately unsaturated (CuS2 motif relative to CuS3 motif). As expected, Au13 Cu3 has an excellent hydrogenation activity of CO2 , in which the current density is as high as 70 mA cm-2 (-0.97 V) and the maximum FECO reaches 99 % at -0.58 V. Through the combination of crystal structures and theoretical calculations, the excellent catalytic activity of Au13 Cu3 is revealed to be indeed closely related to its asymmetric structure.

Cd Atom Goes into the Interior of Cluster Induced by Directional Consecutive Assembly of Tetrahedral Units on an Icosahedron Kernel.

"Core sliding" in metal nanoclusters drives the reconstruction of external structural units and provides an ideal platform for mapping their precise transformation mechanism and evolution pathway. However, observing the movement behavior of metal atoms in experiments is still challenging because of the uncertain stability of intermediates. In this work, a series of Au-Cd alloy nanoclusters with continuously assembled kernels (one icosahedral building block assembled with 0 to 3 tetrahedral units) were constructed. As the assembly continued, it eventually led to the Cd atom doping into the inner positions of the clusters. Importantly, the Cd doped into the interior of the cluster exhibits a different behavior than the surface or external Cd atoms (dispersion doping vs localized occupy), which provides experimental evidence of the sliding behavior in the nanocluster kernel. Furthermore, density functional theory (DFT) calculations reveal that this sliding behavior in the inner sites of nanoclusters is an energetically favorable process. In addition, these Au-Cd nanoclusters exhibit tunable optical properties with different assembly patterns in their kernels.

Mechanistic Study of the Hydride Migration-Induced Reversible Isomerization in Au22(SR)15H Isomers.

Unraveling the evolution mechanism of metal nanoclusters is of great importance in understanding the formation and evolution of metallic condensed matters. In this work, the specific evolution process between a pair of gold nanocluster (Au NC) isomers is completely revealed by introducing hydride ligands to simplify the research system. A hydride-containing Au NC, Au22(SR)15H, was synthesized by kinetic control, and the positions of the hydrides were then confirmed by combining X-ray diffraction, neutron diffraction, and DFT calculations. Importantly, a reversible structural isomerization was found to occur on this Au22(SR)15H. By combining the crystal structures and theoretical calculations, the focus was placed on the hydride-binding site, and a [Au-H] migration mechanism of this isomerization process is clearly shown. Furthermore, this [Au-H] migration mechanism is confirmed by the subsequent capture and structural determination of theoretically predicted intermediates. This work provides insight into the dynamic behavior of hydride ligands in nanoclusters and a strategy to study the evolution mechanism of nanoclusters by taking the hydride ligand as the breakthrough point.

Motif-to-Core Nucleation in a Decahedral Evolution Pattern.

The atomic precision of ultrasmall metal nanoclusters has opened the door to elucidating the structural evolution principles of metal nanomaterials at the molecular level. Here, we report a novel set of super-atomic Ag clusters, including [Ag19(TBBT)16(DPPP)4]+ (Ag19), [Ag22(DMAT)8(DPPM)4Cl8]2+ (Ag22), Ag26(SPh3,5-CF3)15(DPPF)4Cl5 (Ag26), and [Ag30(DMAT)12(DPPP)4Cl8]2+ (Ag30). The core structures of these clusters correspond to one decahedral Ag7, perpendicular bi-decahedrons, three-dimensional penta-decahedrons, and hexa-decahedrons, respectively. The Ag atoms in AgS2 blocks show a strong correlation with the decahedral cores: the five equatorial Ag atoms in the decahedral Ag7 core of Ag19 all adopt the AgS2 coordination, while the Ag atoms in AgS2 blocks of Ag22, Ag26, and Ag30 unexceptionally constitute additional decahedral structures with the core Ag atoms. Specifically, two and four core Ag atoms of Ag26 and Ag30 clusters occupy positions that highly resemble that of Ag (in AgS2 motifs) of Ag22. The strong structural correlation demonstrates the motif-to-core evolution of the surface Ag (on AgS2) to build extra-decahedral blocks. Density functional theory calculations indicate that the 2e, 4e, 6e, and 8e clusters (from Ag19 to Ag30) adopt 1S2, 1S21P2, 1S21P4, and 1S21P6 electron configurations, all of which feature excellent super-atomic characters.

Insight into the Effects of Chiral Diphosphine Ligands on the Structure and Optical Properties of the Au24Cd2 Nanocluster.

Introduction of chiral ligands has been regarded as an effective strategy to obtain nanoclusters with optical purity. However, how the chiral ligands work is still unclear due to the lack of structural comparison between racemic nanoclusters and the corresponding optically active ones. In this work, three structurally related Au24Cd2 nanoclusters, including one racemic and two homochiral nanoclusters, were synthesized, and their crystal structures were characterized using single-crystal X-ray crystallography (SC-XRD). Based on their crystal structures, the origin of the chirality in Au24Cd2 was found to be the twist of the kernel and the chiral arrangement of the metal-ligand surface. Au24Cd2 protected with chiral ligands exhibits a more twisted kernel than the racemic one. Therefore, the chirality of chiral diphosphine was found to transfer from the ligands to the metal-ligand interface and then to the metal core, inducing its distortion to produce enhanced chirality. In addition, the optical properties including optical absorption and circular dichroism of these structurally related Au24Cd2 nanoclusters were compared.

Unraveling the Nucleation Process from a Au(I)-SR Complex to Transition-Size Nanoclusters.

Atomically precise noble metal nanoclusters provide a critical benchmark for the fundamental research of the origin of condensed matter because they retain the original state of the metal bonds. Also, knowledge about the transition from organometallic complexes to a nanoclusters is important for understanding the structural evolution of the nanoclusters, particularly their nucleation mechanism. Herein, three transition-size gold nanoclusters are prepared via a controlled diphosphine-mediated top-down routine. Starting from small-size nanoclusters, three new nanoclusters including Au13(SAdm)8(L4)2(BPh4) (Au13), Au14(S-c-C6H11)10L4 (Au14), and Au16(S-c-C6H11)11LPh* (Au16) are obtained by controlled clipping on the surface and kernel of initial nanoclusters. Combining their atomically precise structures with DFT theoretical calculations, the overall atom-by-atom structural evolution process from Au12(SR)12 (0 e-) to Au18(SR)14 (4 e-) is mapped out. In addition, studies on their electronic structures show that the evolution from an organometallic complex to nanoclusters is accompanied by a dramatic decrease in the HOMO-LUMO gaps. Most importantly, the formation of the first Au-Au bond is captured in the "Au4S4 to Au5" nucleation process from Au12(SR)12 complex to the Au13 nanocluster. This work provides a deep insight into the origin of inner core in Au NCs and their structural transition relationship with metal complexes.

Multiple Ways Realizing Charge-State Transform in AuCu Bimetallic Nanoclusters with Atomic Precision.

Thiolate-protected nanoclusters with different charge states usually show similar structure frameworks but different electronic configurations, which are proved to dramatically affect their properties such as magnetism, photoluminescence, and catalytic activity. Until now, few nanoclusters with alterable charge states have been reported and only some of them are structurally solved, limiting the in-depth studies on their interesting properties. Here, a new AuCu alloy nanocluster [Au18 Cu32 (SPhCl)36 ]2- (HSPhCl = 4-chlorophenylthiophenol) is synthesized and structurally solved by X-ray crystallography. Interestingly, it is found that this nanocluster can be reduced to another nanocluster with a different charge state, that is, [Au18 Cu32 (SPhCl)36 ]3- . This change in charge states is clearly proved by X-ray crystallography, electrospray ionization mass spectrometry, thermogravimetric analysis, and electron paramagnetic resonance. Furthermore, several redox methods are carried out to realize the reversible interconversion between these two nanoclusters, including electrochemical redox, introduction of H2 O2 /NaBH4 , and oxidation with silica under air atmosphere. This work offers new insight into the transform progress of charge states with AuCu alloy nanoclusters which contributes to the understanding of the relationship between electronic structure and properties of nanoclusters and further development of AuCu nanoclusters with excellent performance.

Chiral Inversion and Conservation of Clusters: A Case Study of Racemic Ag32Cu12 Nanocluster.

Chiral metal nanoclusters have been widely reported, but their separation and optical stabilization remain challenging. We used a deracemization strategy to accomplish the enantioseparation of a racemic mixture of [Ag32Cu12(CH3COO)12(SAdm)12(P(CH3OPh)3)4] (M44) in a yield exceeding 50%, forming two optically active [Ag32Cu12(R/S-Cl(CH3)CHCOO)12(SAdm)12(P(CH3OPh)3)4] (R/S-M44') enantiomers. The optical activity of these products was conserved after exchange of the chiral carboxyl ligands with achiral ligand (Br-), to give two additional optically active nanoclusters R/S-[Ag28Cu16Br12(SAdm)12(P(CH3OPh)3)4] (R/S(Br)-M44). The crystal structures of the above nanoclusters were determined by single-crystal X-ray crystallography. Based on these structures, the chiral transformation and conservation are mapped out.

Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations.

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag6 , linear AgS2 (in projection drawing), or tetrahedral AgS3 P binding modes, and the sulfur atoms adopt T-shaped SAg3 and orthogonal SAg4 modes. An additional T-shaped AgS3 mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of µ4 -S or µ4 -Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS3 P motif, regardless of whether the parent NC functions as an electron donor or acceptor.

Exposing the Delocalized Cu-S π Bonds on the Au24 Cu6 (SPhtBu)22 Nanocluster and Its Application in Ring-Opening Reactions.

Bimetallic nanomaterials are of major importance in catalysis. A Au-Cu bimetallic nanocluster was synthesized that is effective in catalyzing the epoxide ring-opening reaction. The catalyst was analyzed by SCXRD and ESI-MS and found to be Au24 Cu6 (SPhtBu)22 (Au24 Cu6 for short). Six copper atoms exclusively occupy the surface positions in two groups with three atoms for each, and each group was bonded with three thiolate ligands to give a planar motif reminiscent of a benzene ring. In the epoxide-ring opening reaction, Au24 Cu6 exhibited superior catalytic activity compared to other homometallic and Au-Cu alloy NCs, such as Au25 and Au38-x Cux . Control experiments and DFT calculations revealed that the π conjugation among the Cu-S bonds played a pivotal role. This study demonstrates a unique π conjugation established among the Cu-S bonds as a critical structural motif in the nanocluster, which facilitates the catalysis of a ring-opening reaction.

Atomically Tailored Gold Nanoclusters for Catalytic Application.

Recent advances in the synthetic chemistry of atomically precise metal nanoclusters (NCs) have significantly broadened the accessible sizes and structures. Such particles are well defined and have intriguing properties, thus, they are attractive for catalysis. Especially, those NCs with identical size but different core (or surface) structure provide unique opportunities that allow the specific role of the core and the surface to be mapped out without complication by the size effect. Herein, we summarize recent work with isomeric Aun NCs protected by ligands and isostructural NCs but with different surface ligands. The highlighted work includes catalysis by spherical and rod-shaped Au25 (with different ligands), quasi-isomeric Au28 (SR)20 with different R groups, structural isomers of Au38 (SR)24 (with identical R) and Au38 S2 (SR)20 with body-centred cubic (bcc) structure, and isostructural [Au38 L20 (PPh3 )4 ]2+ (different L). These isomeric and/or isostructural NCs have provided valuable insights into the respective roles of the kernel, surface staples, and the type of ligands on catalysis. Future studies will lead to fundamental advances and development of tailor-made catalysts.

A Unique Pair: Ag40 and Ag46 Nanoclusters with the Same Surface but Different Cores for Structure-Property Correlation.

Understanding the optical properties of nanoclusters is one of the central tasks in fundamental research. In this work, two new Ag nanoclusters that have distinctly different cores but a common protecting shell are achieved, including [Ag40(2,4-DMBT)24(PPh3)8] and [Ag46(2,5-DMBT)24(PPh3)8]2+. Significantly, the Ag40 nanocluster comprises a simple cubic core of Ag8, which is observed experimentally in the field of metal materials for the first time. Using the Ag40 and Ag46 nanoclusters as a unique pair, we have investigated the effect of core structure on the optical absorption properties of these nanoclusters. The compact core-shell in Ag46 makes the frontier orbitals highly degenerate, whereas the loose core-shell of Ag40 leads to much less degeneracy in the frontier orbits. Overall, this work reveals that the core packing mode plays a significant role in determining the optical properties of metal nanoclusters. The new materials with controlled crystalline phases also hold promise in other applications.

In Situ Two-Phase Ligand Exchange: A New Method for the Synthesis of Alloy Nanoclusters with Precise Atomic Structures.

A new method termed "in situ two-phase ligand exchange" was developed to obtain alloy nanoclusters. With this approach, a series of alloy nanoclusters were obtained for the first time, including Au20Ag1(SR)15, Au21-xAgx(SR)15 (x = 4-8), Au21-xCux(SR)15 (x = 0, 1), and Au21-xCux(SR)15 (x = 2-5) (R = tert-butyl). Interestingly, single-crystal X-ray crystallography (SC-XRD) shows that their frameworks are all alike except for Au21-xCux(SR)15 (x = 2-5), indicating that more Cu dopants alter the structure. Au21-xCux(SR)15 (x = 2-5) exhibits a significantly different configuration. The optical absorption spectra of these bimetal nanoclusters (NCs) show distinct characteristic peaks, indicating that the metal-doping remarkably affects the electronic structure of NCs. The DFT calculations were also employed for determination of NC 1-3 frameworks and understanding their optical properties.

Crystal Structures of Two New Gold-Copper Bimetallic Nanoclusters: CuxAu25-x(PPh3)10(PhC2H4S)5Cl22+ and Cu3Au34(PPh3)13(tBuPhCH2S)6S23.

Herein, we report the synthesis and atomic structures of the cluster-assembled CuxAu25-x(PPh3)10(PhCH2CH2S)5Cl22+ and Cu3Au34(PPh3)13(tBuPhCH2S)6S23+ nanoclusters (NCs). The atomic structures of both NCs were precisely determined by single-crystal X-ray crystallography. The CuxAu25-x(PPh3)10(PhC2H4S)5Cl22+ NC was assembled by two icosahedral M13 via a vertex-sharing mode. The Cu atom partially occupies the top and waist sites and is monocoordinated with chlorine or thiol ligands. Meanwhile, the Cu3Au34(PPh3)13(tBuPhCH2S)6S23+ NC can be described as three 13-atom icosahedra sharing three vertexes in a cyclic fashion. The three Cu atoms all occupy the internal positions of the cluster core. What is more important is that all three Cu atoms in Cu3Au34 are monocoordinated by the bare S atoms. The absorption spectra of the as-synthesized bimetallic NCs reveal that the additional metal doping and different cluster assemblies affect the electronic structure of the monometallic NCs.

A New Crystal Structure of Au36 with a Au14 Kernel Cocapped by Thiolate and Chloride.

This study presents a new crystal structure of a gold nanocluster coprotected by thiolate and chloride, with the formula of Au36(SCH2Ph-(t)Bu)8Cl20. This nanocluster is composed of a Au14 core with two Cl atoms, a pair of pentameric Au5(SCl5) staple motifs, and a pair of hexameric Au6(S3Cl4) motifs. It is noteworthy that the "Au-Cl-Au" staple motifs are observed for the first time in thiolate protected gold nanoclusters. More importantly, the formation of the Cl-Au3 motifs is found to be mainly responsible for the configuration of the gold nanocluster. This work will offer a new perspective to understand how the ligands affect the crystal structure of gold nanocluster.

The Magic Au60 Nanocluster: A New Cluster-Assembled Material with Five Au13 Building Blocks.

Herein, we report the synthesis and atomic structure of the cluster-assembled [Au60Se2(Ph3P)10(SeR)15](+) material. Five icosahedral Au13 building blocks from a closed gold ring with Au-Se-Au linkages. Interestingly, two Se atoms (without the phenyl tail) locate in the center of the cluster, stabilized by the Se-(Au)5 interactions. The ring-like nanocluster is unprecedented in previous experimental and theoretical studies of gold nanocluster structures. In addition, our optical and electrochemical studies show that the electronic properties of the icosahedral Au13 units still remain unchanged in the penta-twinned Au60 nanocluster, and this new material might be a promising in optical limiting material. This work offers a basis for deep understanding on controlling the cluster-assembled materials for tailoring their functionalities.

[Au14(2-SAdm)9(Dppe)2]+: a gold nanocluster with a crystallization-induced emission enhancement phenomenon.

In this work, a gold nanocluster [Au14(2-SAdm)9(Dppe)2]+ was synthesized and structurally determined by X-ray crystallography. The crystals of this cluster exhibit a 50-fold enhancement in quantum yield (5.05% for crystals) compared with its solution. Crystallographic analysis reveals that the weak intermolecular interactions (C-H⋯π, π⋯π) can inhibit the molecular vibration and thus generate the crystallization-induced emission enhancement phenomenon.

Construction of an Au12Cd2 nanocluster with circularly polarized luminescence by a metal- and ligand-exchange strategy.

Excellent luminescence properties and unique chiral structures enable nanoclusters to be a novel class of circularly polarized luminescence (CPL) materials, and their precise structures facilitate the clarification of structure-activity relationships. However, efficiently preparing nanoclusters with CPL properties is still a great challenge. In this work, the luminescent properties as well as the molecular symmetry were simultaneously manipulated to transform the centrosymmetric Au14Cd1 into a chiral Au12Cd2 nanocluster, which has CPL properties. In detail, Cd doping and chiral-ligand exchange were performed simultaneously on the Au14Cd1 nanocluster to realize its photoluminescence enhancement and chiral-framework construction by increasing the alloying degree which is defined as deep-alloying and chiral ligand induction at the same time, resulting in the formation of an Au12Cd2 nanocluster with CPL properties. Further investigations revealed an increased alloying degree in the structure-maintained M6 kernel of Au12Cd2, which results in a 15-fold enhancement in quantum yield.

Insights into mechanisms of diphosphine-mediated controlled surface construction on Au nanoclusters.

Unraveling the rules governing the size regulation of nanoclusters is of great importance not only in fundamental research, but also in practical applications because of the high structure-property correlation in nanoclusters. Diphosphine-mediated size tailoring is recognized as a powerful method for modulating the size, configuration, and properties of nanoclusters, but the role of diphosphines in these size-controlled processes is still poorly understood due to a lack of systematic studies. Herein, using Au23(SR)16- as the template for modification, the factors influencing the size-modulation of nanoclusters by diphosphines were systematically investigated. It is revealed that by controlling the length of the diphosphines (from shorter to longer), Au21(SR)12L2+ (L = diphosphine) and Au22(SR)14L can be produced. Moreover, introducing a rigid group into the diphosphines can twist the structural framework or lead to the formation of a new surface motif configuration in the nanoclusters, forming twisted Au22(SR)14L and Au25(SR)16L2+. The size regulation of these nanoclusters enables fine-tuning of the optical properties, including the absorption wavelengths and photoluminescence emission intensity, affording an avenue for precise control of the physicochemical properties of nanoclusters for practical applications.

H-bond-induced luminescence enhancement in a Pt1Ag30 nanocluster and its application in methanol detection.

Hydrogen bonding is an important type of interaction for constructing nanocluster assemblies. In this study, the role of hydrogen bonding interactions in regulating the fluorescence properties of nanoclusters is investigated. A [Pt1Ag30(SAdm)14(Bdpm)4Cl5]3+ (Pt1Ag30 for short) nanocluster containing hydrogen-accepting ligands is synthesized and its structure is determined. By introducing N-containing ligands into nanoclusters, hydrogen bonding interactions between nanoclusters and polar solvents can be established, which can result in a 35-fold enhancement in the fluorescence intensity (in MeOH vs. in DCM). A series of experiments are designed to demonstrate hydrogen bonding interactions between N atoms in the Pt1Ag30 cluster and H in the polar solvent and the results show that fluorescence enhancement is derived from the proton-coupled/uncoupled electron transfer between hydrogen bonds. Furthermore, this Pt1Ag30 is used for the naked-eye detection of MeOH on indicator paper.