A synchronous nucleation and passivation strategy for controllable synthesis of Au36(PA)24: unveiling the formation process and the role of Au22(PA)18 intermediate

Synthesis of Au13Cu4 Nanoclusters with Isomeric Mercaptobenzoic Acid Ligands

Au-based alloy nanoclusters (NCs) have attracted significant interest due to their unique properties, including chirality, magnetism, luminescence, and size-dependent characteristics. Despite their promising potential, further efforts are required to explore a broader range of ligands and alloy NCs to fully unlock their capabilities. Here, [Au13Cu4(MBA)12]3- alloy NCs (MBA = mercaptobenzoic acid) were synthesized from [Au25(MBA)18]- seed NCs using MBA isomers as etching agents. The [Au25(MBA)18]- NCs were fragmented and reassembled with Cu ions into [Au13Cu4(MBA)12]3- NCs. This process, driven by MBA ligands, was monitored by time-dependent electrospray ionization mass spectrometry and optical spectroscopies. Theoretical calculations suggested a tetrahedral geometry for the [Au13Cu4(MBA)12]3- NCs stabilized by interligand interactions. Notably, the quantum yield of [Au13Cu4(p-MBA)12]3- NCs increased ∼14-fold compared to that of [Au25(p-MBA)18]- NCs. These results offer a novel approach for synthesizing water-soluble, size-focused Au-based alloy NCs, opening up the investigation of new gold alloy clusters with enhanced properties and broader applications.

Halide-Directed Ligand Engineering Enables Expedient, Controlled and Divergent Syntheses of Diphosphine-Protected Au Nanoclusters

Despite substantial progress in ligand engineering, the efforts in the field of Au nanoclusters have been concentrated almost exclusively on organic ligands. Halides, the most typical auxiliary inorganic ligands widely present in Au clusters, remain virtually unexplored, particularly regarding their effects on cluster construction. Herein, diphosphine Ph2P(CH2)nPPh2 (Ln, n = 1-6) is chosen as the co-protecting organic ligands and a comparative analysis on the influential roles of halide ions (Cl-, Br-, I-) in guiding Au cluster synthesis is conducted. A simple yet efficient halide-directed synthetic approach has been developed and a series of Au nanoclusters, including the known [Au18(L1)6Br4]2+, [Au13(L2)5Cl2]3+ and [Au8(L3)4Cl2]2+ that however crystallized in new polymorphic forms, as well as the new reduction-active [Au18(L1)6Cl4]2+, luminescence-enhanced [Au14(L3)5Br4]2+ and core-isomeric [Au11(Ln)4X2]+ (n = 4-6; X = Cl, Br, I), are obtained in a more expedient and controllable manner. This work clearly demonstrates the non-negligible roles of halide ions in directing cluster synthesis, and provides an easier access to diverse diphosphine-protected Au nanoclusters. This approach, promising in gram-scale synthesis, is expected to further extend the ligand scope and holds promise for advancing the diversified syntheses of a broader range of ligand-protected metal nanoclusters.

Atomically Precise Cu Nanoclusters: Recent Advances, Challenges, and Perspectives in Synthesis and Catalytic Applications

Atomically precise metal nanoclusters are an emerging type of nanomaterial which has diverse interfacial metal-ligand coordination motifs that can significantly affect their physicochemical properties and functionalities. Among that, Cu nanoclusters have been gaining continuous increasing research attentions, thanks to the low cost, diversified structures, and superior catalytic performance for various reactions. In this review, we first summarize the recent progress regarding the synthetic methods of atomically precise Cu nanoclusters and the coordination modes between Cu and several typical ligands and then discuss the catalytic applications of these Cu nanoclusters with some explicit examples to explain the atomical-level structure-performance relationship. Finally, the current challenges and future research perspectives with some critical thoughts are elaborated. We hope this review can not only provide a whole picture of the current advances regarding the synthesis and catalytic applications of atomically precise Cu nanoclusters, but also points out some future research visions in this rapidly booming field.

'Passivated Precursor' Approach to All-Alkynyl-Protected Gold Nanoclusters and Total Structure Determination of Au130

A 'passivated precursor' approach is developed for the efficient synthesis and isolation of all-alkynyl-protected gold nanoclusters. Direct reduction of dpa-passivated precursor Au-dpa (Hdpa=2,2'-dipyridylamine) in one-pot under ambient conditions gives a series of clusters including Au22(C≡CR)18 (R=-C6H4-2-F), Au36(C≡CR)24, Au44(C≡CR)28, Au130(C≡CR)50, and Au144(C≡CR)60. These clusters can be well separated via column chromatography. The overall isolation yield of this series of clusters is 40 % (based on gold), which is much improved in comparison with previous approaches. It is notable that the molecular structure of the giant cluster Au130(C≡CR)50 is revealed, which presents important information for understanding the structure of the mysterious Au130 nanoclusters. Theoretical calculations indicated Au130(C≡CR)50 has a smaller HOMO-LUMO gap than Au130(S-C6H4-4-CH3)50. This facile and reliable synthetic approach will greatly accelerate further studies on all-alkynyl-protected gold nanoclusters.

Synthesis, structure anatomy, and catalytic properties of Ag14Cu2 nanoclusters co-protected by alkynyl and phosphine ligands

We report the synthesis, structure anatomy, and catalytic properties of Ag14Cu2(CCArF)14(PPh3)4 (CCArF: 3,5-bis(trifluoromethyl)phenylacetylene) nanoclusters, denoted as Ag14Cu2. Ag14Cu2 has a robust electronic structure with two free valence electrons, and it has a distinctive absorbance feature. Single-crystal X-ray diffraction (SC-XRD) disclosed that Ag14Cu2 possesses an octahedral Ag6 metal kernel capped by two Ag4Cu1(CCArF)7(PPh3)2 metal-ligand units. Remarkably, it exhibits excellent bifunctional catalytic performance for 4-nitrophenol reduction and the electrochemical CO2 reduction reaction (eCO2RR). In 4-nitrophenol reduction, it adopts first-order reaction kinetics with a rate constant of 0.137 min-1, while in the eCO2RR, it shows a CO faradaic efficiency (FECO) of 83.71% and a high current density of 92.65 mA cm-2 at -1.6 V vs. RHE. Moreover, Ag14Cu2 showed robust long-term stability with no significant decay in current density and FECO over 10 h of continuous operation in the eCO2RR. This study not only enriches the potpourri of alkynyl-protected bimetallic AgCu nanoclusters, but also demonstrates the great potential of employing metal nanoclusters for bifunctional catalytic applications.

A homoleptic alkynyl-protected [Ag9Cu6( t BuC[triple bond, length as m-dash]C)12]+ superatom with free electrons: synthesis, structure analysis, and different properties compared with the Au7Ag8 cluster in the M15 + series

We report the first homoleptic alkynyl-protected AgCu superatomic nanocluster [Ag9Cu6( t BuC[triple bond, length as m-dash]C)12]+ (NC 1, also Ag9Cu6 in short), which has a body-centered-cubic structure with a Ag1@Ag8@Cu6 metal core. Such a configuration is reminiscent of the reported AuAg bimetallic nanocluster [Au1@Ag8@Au6( t BuC[triple bond, length as m-dash]C)12]+ (NC 2, also Au7Ag8 in short), which is also synthesized by an anti-galvanic reaction (AGR) approach with a very high yield for the first time in this study. Despite a similar Ag8 cube for both NCs, structural anatomy reveals that there are some subtle differences between NCs 1 and 2. Such differences, plus the different M1 kernel and M6 octahedron, lead to significantly different optical absorbance features for NCs 1 and 2. Density functional theory calculations revealed the LUMO and HOMO energy levels of NCs 1 and 2, where the characteristic absorbance peaks can be correlated with the discrete molecular orbital transitions. Finally, the stability of NCs 1 and 2 at different temperatures, in the presence of an oxidant or Lewis base, was investigated. This study not only enriches the M15 + series, but also sets an example for correlating the structure-property relationship in alkynyl-protected bimetallic superatomic clusters.

Assembly of Chiral Cluster-Based Metal-Organic Frameworks and the Chirality Memory Effect during their Disassembly

Many metal clusters are intrinsically chiral but are often synthesized as a racemic mixture. By taking chiral Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(DMF)₄ (Ag₁₄) clusters with bulky thiolate ligands as an example, we demonstrate herein an interesting assembly disassembly (ASDS) strategy to obtain the corresponding, optically pure crystals of both homochiral enantiomers, R-Ag_14m and S-Ag_14m. The ASDS strategy makes use of two bidentate linkers with different chiral configurations, namely, (1R,2R,N¹E,N²E)-N¹,N²-bis(pyridin-3-ylmethylene)cyclohexane-1,2-diamine (LR) and the corresponding chiral analogue LS. For comparison, we also use the racemic mixture of equimolar of LR and LS (LRS). Three three-dimensional (3D) Ag₁₄-based metal-organic frameworks (MOFs) were characterized by X-ray crystallography to be [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LR)₂]_n (Ag₁₄-LR), [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LS)₂]_n (Ag₁₄-LS), and [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LRS)₂]_n (Ag₁₄-LRS), respectively. As expected, the building blocks in Ag₁₄-LR or Ag₁₄-LS are homochiral R-Ag₁₄ or S-Ag₁₄, respectively. In contrast, Ag₁₄-LRS is achiral and crystallizes with a diamond-like structure containing alternate R-Ag₁₄ and S-Ag₁₄ clusters. During the assembly process, the racemic Ag₁₄ clusters were converted to homochiral building blocks, namely, R-Ag₁₄ for Ag₁₄-LR and S-Ag₁₄ for Ag₁₄-LS. Subsequently, the chiral linkers were removed from the crystals of Ag₁₄-LR and Ag₁₄-LS via hydrolysis with water, and from the disassembled solid material Ag₁₄-DR and Ag₁₄-DS, optically pure enantiomers R-Ag_14m and S-Ag_14m were obtained. It is hoped that this simple assembly strategy can be used to construct cluster-based chiral assemblage materials and that the subsequent disassembly protocol can be used to obtain optically pure chiral cluster molecules from as-prepared racemic mixtures.

Controllable synthesis and formation mechanism study of homoleptic alkynyl-protected Au nanoclusters: recent advances, grand challenges, and great opportunities

In the past decade, atomically precise coinage metal nanoclusters have been a subject of major interest in nanoscience and nanotechnology because of their determined compositions and well-defined molecular structures, which are beneficial for establishing structure-property relationships. Recently ligand engineering has been extended to alkynyl molecules. Homoleptic alkynyl-protected Au nanoclusters (Au NCs) have emerged as a hotspot of research interest, mainly due to their unique optical properties, molecular configuration, and catalytic functionalities, and more importantly, they are used as a counterpart object for fundamental study to compare with the well-established thiolate Au NCs. In this review, we first summarize the recently reported various controllable synthetic strategies for atomically precise homoleptic-alkynyl-protected Au NCs, with particular emphasis on the ligand exchange method, direct reduction of the precursor, one-pot synthesis, and the synchronous nucleation and passivation strategy. After that, we switch our focus to the formation mechanism and structure evolution process of homoleptic alkynyl-protected Au NCs, where Au144(PA)60 and Au36(PA)24 (PA = phenylacetylide) are given as examples, along with the prediction of the possible formation mechanism of some other cluster molecules. In the end of this review, the outlook and perspective of this rapidly developing field including grand challenges and great opportunities are discussed. This review can stimulate more research efforts towards developing new synthetic strategies to enrich the limited examples and unravel the formation/growth mechanism of homoleptic alkynyl-protected Au NCs.