Solvent-Controlled Condensation of [Mo2 O5 (PTC4A)2 ]6- Metalloligand in Stepwise Assembly of Hexagonal and Rectangular Ag18 Nanoclusters

A 66-Nuclear All-Alkynyl Protected Peanut-Shaped Silver(I)/Copper(I) Heterometallic Nanocluster: Intermediate in Copper-Catalyzed Alkyne-Azide Cycloaddition

Ligand-protected heterometallic nanoclusters in contrast to homo-metal counterparts show more broad applications due to the synergistic effect of hetero-metals but their controllable syntheses remain a challenge. Among heterometallic nanoclusters, monovalent Ag-Cu compounds are rarely explored due to much difference of Ag(I) and Cu(I) such as atom radius, coordination habits, and redox potential. Encouraged by copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, comproportionation reaction of Cu(II)X2 and Cu(0) in the presence of (PhC≡CAg)n complex and molybdate generated a core-shell peanut-shaped 66-nuclear Ag(I)-Cu(I) heterometallic nanocluster, [(Mo4O16)2@Cu12Ag54(PhC≡C)50] (referred to as Ag54Cu12). The structure and composition of Ag-Cu heterometallic nanocluster are fully characterized. X-ray single crystal diffraction reveals that Ag54Cu12 has a peanut-shaped silver(I)/copper(I) heterometallic nanocage protected by fifty phenylacetylene ligands in µ3-modes and encapsulated two mutually twisted tetramolybdates. Heterometallic nanocage contains a 54-Ag-atom outer ellipsoid silver cage decorated by 12 copper inside wall. Nanosized Ag54Cu12 is a n-type narrow-band-gap semiconductor with a good photocurrent response. Preliminary experiments demonstrates that Ag54Cu12 itself and activated carbon supported Ag54Cu12/C are effective catalysts for 1,3-dipole cycloaddition between alkynes and azides at ambient conditions. The work provides not only a new synthetic route toward Ag(I)-Cu(I) nanoclusters but also an important heterometallic intermediate in CuAAC catalytic reaction.

Ag1+ incorporation via a Zr4+-anchored metalloligand: fine-tuning catalytic Ag sites in Zr/Ag bimetallic clusters for enhanced eCO2RR-to-CO activity

Attaining meticulous dominion over the binding milieu of catalytic metal sites remains an indispensable pursuit to tailor product selectivity and elevate catalytic activity. By harnessing the distinctive attributes of a Zr4+-anchored thiacalix[4]arene (TC4A) metalloligand, we have pioneered a methodology for incorporating catalytic Ag1+ sites, resulting in the first Zr-Ag bimetallic cluster, Zr2Ag7, which unveils a dualistic configuration embodying twin {ZrAg3(TC4A)2} substructures linked by an {AgSal} moiety. This cluster unveils a trinity of discrete Ag sites: a pair ensconced within {ZrAg3(TC4A)2} subunits and one located between two units. Expanding the purview, we have also crafted ZrAg3 and Zr2Ag2 clusters, meticulously mimicking the two Ag site environment inherent in the {ZrAg3(TC4A)2} monomer. The distinct structural profiles of Zr2Ag7, ZrAg3, and Zr2Ag provide an exquisite foundation for a precise comparative appraisal of catalytic prowess across three Ag sites intrinsic to Zr2Ag7. Remarkably, Zr2Ag7 eclipses its counterparts in the electroreduction of CO2, culminating in a CO faradaic efficiency (FECO) of 90.23% at -0.9 V. This achievement markedly surpasses the performance metrics of ZrAg3 (FECO: 55.45% at -1.0 V) and Zr2Ag2 (FECO: 13.09% at -1.0 V). Utilizing in situ ATR-FTIR, we can observe reaction intermediates on the Ag sites. To unveil underlying mechanisms, we employ density functional theory (DFT) calculations to determine changes in free energy accompanying each elementary step throughout the conversion of CO2 to CO. Our findings reveal the exceptional proficiency of the bridged-Ag site that interconnects paired {ZrAg3(TC4A)2} units, skillfully stabilizing *COOH intermediates, surpassing the stabilization efficacy of the other Ag sites located elsewhere. The invaluable insights gleaned from this pioneering endeavor lay a novel course for the design of exceptionally efficient catalysts tailored for CO2 reduction reactions, emphatically underscoring novel vistas this research unshrouds.

Eight-Electron Copper Nanoclusters for Photothermal Conversion

Owing to distinct physicochemical properties in comparison to gold and silver counterparts, atomically precise copper nanoclusters are attracting embryonic interest in material science. The introduction of copper cluster nanomaterials in more interesting fields is currently urgent and desired. Reported in this work are novel copper nanoclusters of [XCu54Cl12(tBuS)20(NO3)12] (X=S or none, tBuSH=2-methyl-2-propanethiol), which exhibit high performance in photothermal conversion. The clusters have been prepared in one pot and characterized by combinatorial techniques including ultraviolet-visible spectroscopy (UV-vis), electrospray ionization mass spectrometry (ESI-MS), and X-ray photoelectron spectroscopy (XPS). The molecular structure of the clusters, as revealed by single crystal X-ray diffraction analysis (SCXRD), shows the concentric three-shell Russian doll arrangement of X@Cu14@Cl12@Cu40. Interestingly, the [SCu54Cl12(tBuS)20(NO3)12] cluster contains 8 free valence electrons in its structure, making it the first eight-electron copper nanocluster stabilized by thiolates. More impressively, the clusters possess an effective photothermal conversion (temperature increases by 71 °C within ~50 s, λex=445 nm, 0.5 W cm-2) in a wide wavelength range (either blue or near-infrared). The photothermal conversion can be even driven under irradiation of simulated sunlight (3 sun), endowing the clusters with great potency in solar energy utilization.

An Au5Ag12(SR)9(dppf)4 alloy nanocluster: structural determination and optical property and photothermal conversion investigation

Photothermal conversion has garnered significant attention due to its potential for efficient energy conversion and application in targeted therapies. However, controlling photothermal properties at the atomic level remains a challenge in current materials synthesis. In this study, we report the synthesis and structural determination of a phosphine and mercaptan co-protected Au5Ag12(SR)9(dppf)4 (Au5Ag12) nanocluster with an extremely low quantum yield (∼0%). For comparative purposes, we synthesized three alloy nanoclusters of similar size. Notably, Au5Ag12 demonstrates a remarkably superior photothermal conversion performance, significantly outperforming the other clusters. We investigated this variance from both absorption and emission perspectives. This research not only opens new avenues for the application of clusters with extremely low quantum yields, but also provides experimental evidence for understanding the photothermal conversion properties of cluster materials at the atomic level.

Three in One: Three Different Molybdates Trapped in a Thiacalix[4]arene Protected Ag72 Nanocluster for Structural Transformation and Photothermal Conversion

Polyoxometalates (POMs) represent crucial intermediates in the formation of insoluble metal oxides from soluble metal ions, however, the rapid hydrolysis-condensation kinetics of MoVI or WVI makes the direct characterization of coexisted molecular species in a given medium extremely difficult. Silver nanoclusters have shown versatile capacity to encapsulate diverse POMs, which provides an alternative scene to appreciate landscape of POMs in atomic precision. Here, we report a thiacalix[4]arene protected silver nanocluster (Ag72b) that simultaneously encapsulates three kinds of molybdates (MoO4 2- , Mo6 O22 8- and Mo7 O25 8- ) in situ transformed from classic Lindqvist Mo6 O19 2- , providing more deep understanding on the structural diversity and condensation growth route of POMs in solution. Ag72b is the first silver nanocluster trapping so many kinds of molybdates, which in turn exert collective template effect to aggregate silver atoms into a nanocluster. The post-reaction of Ag72b with AgOAc or PhCOOAg produces a discrete Ag24 nanocluster (Ag24a) or an Ag28 nanocluster based 1D chain structure (Ag28a), respectively. Moreover, the post-synthesized Ag28a can be utilized as potential ignition material for further application. This work not only provides an important model for unlocking dynamic features of POMs at atom-precise level but also pioneers a promising approach to synthesize silver nanoclusters from known to unknown.

Stepwise formation of a chemodynamic therapy agent of {Cu8} macrocyclic complex recognized by iodide ions

An atomically precise Cu(I) macrocyclic complex Cu8I was developed for chemodynamic therapy (CDT) research. The {Cu8} macrocyclic skeleton gradually forms with the selective recognition of iodide ions, and the monitoring of intermediate fragments during Cu8I formation using time-dependent electrospray ionization mass spectrometry indicates the following possible formation process: [Cu1] → [Cu2] → [Cu3] → [Cu4] → [Cu5I] → [Cu6I] → [Cu7I] → [Cu8I] when recognized by iodide ions. Furthermore, the Cu(I)-mediated Fenton-like reaction in Cu8I catalyzes the production of toxic ˙OH from H2O2, which results in efficient tumor suppression.

Stepwise assembly of thiacalix[4]arene-protected Ag/Ti bimetallic nanoclusters: accurate identification of catalytic Ag sites in CO2 electroreduction

The accurate identification of catalytic sites in heterogeneous catalysts poses a significant challenge due to the intricate nature of controlling interfacial chemistry at the molecular level. In this study, we introduce a novel strategy to address this issue by utilizing a thiacalix[4]arene (TC4A)-protected Ti-oxo core as a template for loading Ag1+ ions, leading to the successful synthesis of a unique Ag/Ti bimetallic nanocluster denoted as Ti8Ag8. This nanocluster exhibits multiple surface-exposed Ag sites and possesses a distinctive "core-shell" structure, consisting of a {Ti4@Ag8(TC4A)4} core housing a {Ti2O2@Ag4(TC4A)2} motif and two {Ti@Ag2(TC4A)} motifs. To enable a comprehensive analysis, we also prepared a Ti2Ag4 cluster with the same {Ti2O2@Ag4(TC4A)2} structure found within Ti8Ag8. The structural disparities between Ti8Ag8 and Ti2Ag4 provide an excellent platform for a comparison of catalytic activity at different Ag sites. Remarkably, Ti8Ag8 exhibits exceptional performance in the electroreduction of CO2 (eCO2RR), showcasing a CO faradaic efficiency (FECO) of 92.33% at -0.9 V vs. RHE, surpassing the FECO of Ti2Ag4 (69.87% at -0.9 V vs. RHE) by a significant margin. Through density functional theory (DFT) calculations, we unveil the catalytic mechanism and further discover that Ag active sites located at {Ti@Ag2(TC4A)} possess a higher εd value compared to those at {Ti2O2@Ag4(TC4A)2}, enhancing the stabilization of the *COOH intermediate during the eCO2RR. This study provides valuable insights into the accurate identification of catalytic sites in bimetallic nanoclusters and opens up promising avenues for efficient CO2 reduction catalyst design.

Thiacalix[4]arene-protected alkynyl Agn (n = 9, 18) nanoclusters: syntheses, structural characterizations, photocurrent responses and fluorescence properties

Two thiacalix[4]arene-protected silver(I) alkynyl nanoclusters, [Na2(H2O)2][Ag9(TC4A)(tBuCC)4(CH3OH)2(SbF6)0.5(OH)2.5]·3.5H2O·CH3OH (1, abbreviated as Ag9) and [Ag9(TC4A)(tBuCC)4(CF3COO)]2·4CH3OH (2, abbreviated as Ag18), were synthesized by the reaction of [tBuCCAg]n, p-tert-butylthiacalix[4]arene (H4TC4A), NaBH4, and AgSbF6 or CF3COOAg in the mixed solvent of methanol-trichloromethane-toluene under solvothermal conditions, respectively. Driven by SbF6- and CF3COO- with different coordination properties, the structural unit [Ag9(TC4A)(tBuCC)4]+ in both the compounds migrated in different modes, accompanied by distinct Ag⋯Ag distances. Ag9 and Ag18 exhibit similar UV-Vis absorption and diffuse reflection spectra along with contrary tendency between photocurrent responses and solid-state fluorescence. The solution stability of Ag9 and Ag18 was demonstrated by 1H NMR and MALDI-TOF mass spectrometry. The fluorescence responses of Ag9 and Ag18 towards different organic molecules were also investigated, which indicated that the polarity of solvent has a certain effect on the emission intensities of Ag9 and Ag18. This study provides a positive guide for the controlled synthesis and further study of the structure-activity relationship of thiacalix[4]arene-protected silver alkynyl nanoclusters.

Unveiling the Remarkable Stability and Catalytic Activity of a 6-Electron Superatomic Ag30 Nanocluster for CO2 Electroreduction

Nanocluster catalysts face a significant challenge in striking the right balance between stability and catalytic activity. Here, we present a thiacalix[4]arene-protected 6-electron [Ag30(TC4A)4(iPrS)8] nanocluster that demonstrates both high stability and catalytic activity. The Ag30 nanocluster features a metallic core, Ag104+, consisting of two Ag3 triangles and one Ag4 square, shielded by four {Ag5@(TC4A)4} staple motifs. Based on DFT calculations, the Ag104+ metallic kernel can be viewed as a trimer comprising 2-electron superatomic units, exhibiting a valence electron structure similar to that of the Be3 molecule. Notably, this is the first crystallographic evidence of the trimerization of 2-electron superatomic units. Ag30 can reduce CO2 into CO with a Faraday efficiency of 93.4% at -0.9 V versus RHE along with excellent long-term stability. Its catalytic activity is far superior to that of the chain-like AgI polymer ∞1{[H2Ag5(TC4A)(iPrS)3]} (∞1Agn), with the composition similar to Ag30. DFT calculations elucidated the catalytic mechanism to clarify the contrasting catalytic performances of the Ag30 and ∞1Agn polymers and disclosed that the intrinsically higher activity of Ag30 may be due to the greater stability of the dual adsorption mode of the *COOH intermediate on the metallic core.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

A route to metalloligands consolidated silver nanoclusters by grafting thiacalix[4]arene onto polyoxovanadates

Metalloligands provide a potent strategy for manipulating the surface metal arrangements of metal nanoclusters, but their synthesis and subsequent installation onto metal nanoclusters remains a significant challenge. Herein, two atomically precise silver nanoclusters {Ag14[(TC4A)6(V9O16)](CyS)3} (Ag14) and {Ag43S[(TC4A)2(V4O9)]3(CyS)9(PhCOO)3Cl3(SO4)4(DMF)3·6DMF} (Ag43) are synthesized by controlling reaction temperature (H4TC4A = p-tert-butylthiacalix[4]arene). Interestingly, the 3D scaffold-like [(TC4A)6(V9O16)]11- metalloligand in Ag14 and 1D arcuate [(TC4A)2(V4O9)]6- metalloligand in Ag43 exhibit a dual role that is the internal polyoxovanadates as anion template and the surface TC4A4- as the passivating agent. Furthermore, the thermal-induced structure transformation between Ag14 and Ag43 is achieved based on the temperature-dependent assembly process. Ag14 shows superior photothermal conversion performance than Ag43 in solid state indicating its potential for remote laser ignition. Here, we show the potential of two thiacalix[4]arene modified polyoxovanadates metalloligands in the assembly of metal nanoclusters and provide a cornerstone for the remote laser ignition applications of silver nanoclusters.

Solvent-Induced Modulation in the Optical Properties of Copper Nanoclusters and Revealing the Isomeric Effect of Templates

The solvent plays an influential role in controlling the nucleation process of metal nanoclusters (MNCs) and thereby significantly modulates their optical signatures. Herein, we have demonstrated the solvent-induced modulation in the optical properties of copper nanoclusters (CuNCs), primarily governed by the solvent polarity. During the preparation of para-mercaptobenzoic acid (p-MBA)-templated CuNCs, the simultaneous formation of blue-emitting CuNCs (B-CuNCs) and red-emitting CuNCs (R-CuNCs) were observed up to 7 h of reaction time, reflected from the systematic increment in the photoluminescence (PL) intensity at 420 nm and 615 nm, respectively. However, after 7 h of reaction time, the exclusive formation of B-CuNCs was observed. Such simultaneous growth and depletion dynamics of CuNCs result in a significant modulation in their optical properties. The variation of the solvent from water to less polar solvents such as DMSO and DMF restricts this inter-cluster dynamics by stabilizing both the CuNCs (B-CuNCs and R-CuNCs). Thereby, a single-component White Light Emission (WLE) was realized in DMSO with CIE coordinates (0.37, 0.36). The isomeric effect of the templates has also been investigated which extensively controls the optical and catalytic properties of the CuNCs.

Solvent-Mediated Separation and Reversible Transformation of 1D Supramolecular Polymorphs Built from [W10O32]4- Templated 48-Nuclei Silver(I) Cluster

Although the C-H···O interaction is an essential component in determining the molecular packing in solids and the properties in supramolecular chemistry, it presents a significant challenge when trying to use it in the crystal engineering of complex metallosupramolecules, even though it is a relatively weak supramolecular force. The first pair of high-nuclearity silver-cluster-based one-dimensional (1D) polymorphs built from supramolecular synthon [W₁₀O₃₂@Ag₄₈(CyS)₂₄(NO₃)₁₆]·4NO₃ (Cy = cyclohexyl) bridged by four grouped inorganic NO₃^- ligands is initially synthesized as a mixed phase and further individually crystallized as a pure phase by virtue of tuning intermolecular C-H···O interaction through altering the composition ratio of ternary solvent system. Increasing highly polar and hydrogen-bonding methanol strengthens the solvation effect reflected by the change of coordination orientation of surface NO₃^- ligands, which dominates the packing of the 1D chains in the crystal lattice, resulting in the crystallization of polymorphs from tetragonal to monoclinic. The two crystalline forms can also be reversibly transformed to each other in an appropriate solvent system. Correspondingly, the two polymorphs display distinct temperature-dependent photoluminescence behaviors, which are ascribed to the variation of noncovalent interchain C-H···O interactions along with the temperature. More importantly, benefiting from the suppression of fluorescence, both polymorphs offer excellent photothermal conversion properties which were further applied to remote-controlled laser ignition. These findings may open more avenues for the application of solvent-mediated intermolecular interaction in controlling the molecule arrangement as well as the optical properties.

Structural Engineering toward Gold Nanocluster Catalysis

Atomically precise gold nanoclusters provide great opportunities to explore the relationship between the structure and properties of nanogold catalysts. A nanocluster consists of a metal core and a surface ligand shell, and both the core and shell have significant effects on the catalytic properties. Thanks to their precise structures, the active metal site of the clusters can be readily identified and the effects of ligands on catalysis can be disclosed. In this Minireview, we summarize recent advances in catalytic research of gold nanoclusters, emphasizing four strategies for constructing open metal sites, including by post-treatment, the bulky ligands strategy, the surface geometric mismatch method, and heteroatom doping procedures. We also discuss the effects of ligands on the catalytic activity, selectivity, and stability of gold cluster catalysts. Finally, we present future challenges relating to gold cluster catalysis.

Mapping H+ in the Nanoscale (A2C4)2-Ag8 Fluorophore

When strands of DNA encapsulate silver clusters, supramolecular optical chromophores develop. However, how a particular structure endows a specific spectrum remains poorly understood. Here, we used neutron diffraction to map protonation in (A₂C₄)₂-Ag₈, a green-emitting fluorophore with a "Big Dipper" arrangement of silvers. The DNA host has two substructures with distinct protonation patterns. Three cytosines from each strand collectively chelate handle-like array of three silvers, and calorimetry studies suggest Ag⁺ cross-links. The twisted cytosines are further joined by hydrogen bonds from fully protonated amines. The adenines and their neighboring cytosine from each strand anchor a dipper-like group of five silvers via their deprotonated endo- and exocyclic nitrogens. Typically, exocyclic amines are strongly basic, so their acidification and deprotonation in (A₂C₄)₂-Ag₈ suggest that silvers perturb the electron distribution in the aromatic nucleobases. The different protonation states in (A₂C₄)₂-Ag₈ suggest that atomic level structures can pinpoint how to control and tune the electronic spectra of these nanoscale chromophores.

Oxocarbon Anions Templated in Silver Clusters

Three types of oxocarbon anions as templates were used to synthesize high-nuclear silver clusters, [Ag₁₆(C₂O₄){S₂P(OEt)₂}₁₂]₂(PF₆)₄ (1), [Ag₁₆(C₄O₄){S₂P(OEt)₂}₁₂]₂(PF₆)₄ (2), and [Ag₃₂(S)₂(C₅O₅)₂{S₂P(OEt)₂}₂₂](PF₆)₂ (3), and characterized by multi-NMR spectroscopy and X-ray crystallography. As the template size increases, the shape and size of the clusters change accordingly. The template effect in high-nuclear silver clusters has been investigated in this work.