Anion Encapsulation and Geometric Changes in Hepta- and Hexanuclear Copper(I) Dichalcogeno Clusters: A Theoretical and Experimental Investigation

Exploring the structural evolution of Cu-thiolate nanoclusters and their property correlations

Research on copper nanoclusters (Cu NCs) is expanding rapidly due to their remarkable structural versatility and related tunable properties they exhibit. This fast-paced development creates a need for a comprehensive overview of the structural evolution of Cu NCs, especially regarding how different geometric configurations emerge from variations in the ligand choice. In light of this, this feature article focuses on the role of thiolate ligands in shaping the structural and electronic properties of Cu NCs, with a particular emphasis on how modifications of ligands influence the geometry of NCs. While thiolates play a central role in stabilizing Cu NCs, this feature article also underscores the significance of co-ligands-such as hydrides, phosphines, and halides-because relying solely on thiolates is often insufficient to fully protect the surface of Cu NCs, unlike in the case of gold or silver NCs. A detailed analysis of how various thiolates and co-ligands affect core geometry reveals a direct correlation with the electronic properties of Cu NCs, which in turn influences their optical behavior. By examining these ligand-driven structural and electronic changes, this feature article aims to provide a deeper understanding of the relationship between ligand design and the resulting NC properties. The ultimate goal is to offer a strategy for the rational design of Cu NCs with tailored functionalities, thereby advancing NC chemistry and opening up new possibilities for applications in optoelectronics, catalysis, and sensing.

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

Hydride-Containing Pt-doped Cu-rich Nanoclusters: Synthesis, Structure, and Electrocatalytic Hydrogen Evolution

A structurally precise hydride-containing Pt-doped Cu-rich nanocluster [PtH2 Cu14 {S2 P(Oi Pr)2 }6 (CCPh)6 ] (1) has been synthesized. It consists of a bicapped icosahedral Cu14 cage that encapsulates a linear PtH2 unit. Upon the addition of two equivalents of CF3 COOH to 1, two hydrido clusters are isolated. These clusters are [PtHCu11 {S2 P(Oi Pr)2 }6 (CCPh)4 ] (2), which is a vertex-missing Cu11 cuboctahedron encaging a PtH moiety, and [PtH2 Cu11 {S2 P(Oi Pr)2 }6 (CCPh)3 ] (3), a distorted 3,3,4,4,4-pentacapped trigonal prismatic Cu11 cage enclosing a PtH2 unit. The electronic structure of 2, analyzed by Density Functional Theory, is a 2e superatom. The electrocatalytic activities of 1-3 for hydrogen evolution reaction (HER) were compared. Notably, Cluster 2 exhibited an exceptionally excellent HER activity within metal nanoclusters, with an onset potential of -0.03 V (at 10 mA cm-2 ), a Tafel slope of 39 mV dec-1 , and consistent HER activity throughout 3000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pt site plays a crucial role in the remarkable HER activity and may provide valuable insights for establishing correlations between catalyst structure and HER activity.

Recent progress in dichalcophosphate coinage metal clusters and superatoms

Atomically precise clusters of group 11 metals (Cu, Ag, and Au) attract considerable attention owing to their remarkable structure and fascinating properties. One of the unique subclasses of these clusters is based on dichalcophosphate ligands of [(RO)₂PE₂]^- type (E = S or Se, and R = alkyl). These ligands successfully stabilise the most diverse Cu, Ag, and Au clusters and superatoms, spanning from simple ones to amazing assemblies featuring unusual structural and bonding patterns. It is noteworthy that such complicated clusters are assembled directly from cheap and simple reagents, metal(I) salts and dichalcophosphate anions. This reaction, when performed in the presence of a hydride or other anion sources, or foreign metal ions, results in hydrido- or anion-templated homo- or heteronuclear structures. In this feature article, we survey the recent advances in this exciting field, highlighting the powerful synthetic capabilities of the system "a metal(I) salt - [(RO)₂PX₂]^- ligands - a templating anion or borohydride" as an inexhaustible platform for the creation of new atomically precise clusters, superatoms, and nanoalloys.

Heptanuclear Silver Hydride Clusters as Catalytic Precursors for the Reduction of 4-Nitrophenol

We report on the design, synthesis, and characterization of the first silver hydride clusters solely protected and stabilized by dithiophosphonate ligands and their application for the in situ generation of silver nanoparticles towards the catalytic reduction of 4-nitrophenol in an aqueous system. The synthesis of the silver monohydride cluster involves the incorporation of an interstitial hydride using sodium borohydride. Poly-nuclear magnetic resonance and mass spectrometry were used to establish the structural properties. The structural properties were then confirmed with a single-crystal X-ray diffraction analysis, which showed a distorted tetracapped tetrahedron core with one hydride ion encapsulated within the core of the silver framework. Additionally, the synthesized heptanuclear silver hydride was utilized as a precursor for the in situ generation of silver nanoparticles, which simultaneously catalyzed the reduction of 4-nitrophenol. The mechanism of the catalytic activity was investigated by first synthesizing AgNPs, which was subsequently used as a catalyst. The kinetic study showed that the pseudo-first constant obtained using the cluster (2.43 × 10−2 s−1) was higher than that obtained using the synthesized AgNPs (2.43 × 10−2 s−1). This indicated that the silver monohydride cluster was more active owing to the release of the encapsulated hydride ion and greater reaction surface prior to aggregation.

Interstitial hydrides in nanoclusters can reduce M(I) (M = Cu, Ag, Au) to M(0) and form stable superatoms

High-nuclearity clusters resemble the closest model between the determination of atomically precise chemical species and the bulk metallic version thereof, and both impacts on a variety of applications, including catalysis, optics, sensors, and new energy sources.  Our interest lies with the nanoclusters of the Group 11 (Cu, Ag, Au) metals stabilized by dichalcogenido and hydrido ligands.  Herein, we describe superatoms formed by the clusters and their relationship with precursor hydrido clusters.  Specifically, our concept seeks to demonstrate a possible correlation that exist between hydrido clusters (and nanoalloys) and the formation of superatoms, with the loss of hydrides and typically with release of H 2 gas.  These reactions appear to be internal self-redox reactions and require no additional reducing agent, but does seem to require a similar core structure.  Knowledge of such processes could provide insight into how clusters grow and an understanding in bridging the atomically precise cluster - metal nanoparticle mechanism.

Locating Hydrides in Ligand-Protected Copper Nanoclusters by Deep Learning

Hydrides play an important role in constructing atomically precise metal nanoclusters and nanoparticles. They occupy both the interstitial sites inside the metal cores and the interfacial sites between the surface of the metal core and the ligand layer. Although the heavy-atom positions can be routinely determined by single-crystal X-ray diffraction, the challenge in growing a large and high-enough-quality single crystal for neutron diffraction and the limited availability of neutron sources have prevented researchers from precisely knowing the hydride locations. A recently developed deep-learning method showed great promise in accelerating the determination of hydride sites in metal nanostructures, but it is unclear if this approach, trained on clusters up to Cu₃₂ in size, can be applied to recently discovered, much larger nanoclusters such as Cu₈₁. Here we show that an improved deep-learning model based on convolutional neural networks is both accurate and robust. We apply it to two recently reported copper nanoclusters, [Cu₃₂(PET)₂₄H₈Cl₂]^2- and [Cu₈₁(PhS)₄₆(^tBuNH₂)₁₀H₃₂]³⁺, whose hydride locations have not been determined by neutron but were proposed from density functional theory (DFT) calculations. In the former, our CNN model confirms the DFT structure; in the latter, our CNN model predicts a more stable structure with different hydride sites.

Intercluster exchanges leading to hydride-centered bimetallic clusters: a multi-NMR, X-ray crystallographic, and DFT study

Encouraged by the successful syntheses of alloy nanoclusters (or nanoparticles) via intercluster (or interparticle) reactions, herein we apply this methodology to prepare a series of bimetallic hydride clusters. Mixing of two clusters, [Ag₇(H){E₂P(OⁱPr)₂}₆] (E = S, 1; Se, 3) and [Cu₇(H){E₂P(OⁱPr)₂}₆] (E = S, 2; Se, 4), yields two series of hydride-centered bimetallic clusters, [Cu_xAg_7-x(H){E₂P(OⁱPr)₂}₆] (x = 0-7; E = S, 5; Se, 6). Their compositions are fully characterized by positive-mode ESI-MS spectrometry, multi-NMR spectroscopy, and the structures of [Cu₆Ag(H){S₂P(OⁱPr)₂}₆] (5a) and [CuAg₆(H){Se₂P(OⁱPr)₂}₆] (6a) by single crystal X-ray diffraction. The presence of individual compounds in solution is the result of a (dynamic) chemical equilibrium primarily driven by metal exchanges. In fact, the process of inter-cluster exchange of 1 and 2 leading to hydride-centered bimetallic clusters 5 can be monitored by concentration-dependent ³¹P NMR spectroscopy of which the higher concentration of 1 in the reaction, the closer to its resonance will be the distribution, in accord with Le Chatelier's principle. The dynamic equilibrium is further confirmed by 2D exchange spectroscopy that reveals a stepwise process involving one metal exchange at a time. DFT calculations on a model series of clusters 6 show that silver prefers occupying the inner tetrahedral positions, while copper favors capping positions, in full agreement with the crystal structure of 5a and 6a.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Exploring Cu/Al cluster growth and reactivity: from embryonic building blocks to intermetalloid, open-shell superatoms

Cluster growth reactions in the system [Cu5](Mes)5 + [Al4](Cp*)4 (Mes = mesitylene, Cp* = pentamethylcyclopentadiene) were explored and monitored by in situ LIFDI-MS and 1H-NMR. Feedback into experimental design allowed for an informed choice and precise adjustment of reaction conditions and led to isolation of the intermetallic cluster [Cu4Al4](Cp*)5(Mes) (1). Cluster 1 reacts with excess 3-hexyne to yield the triangular cluster [Cu2Al](Cp*)3 (2). The two embryonic [Cu4Al4](Cp*)5(Mes) and [Cu2Al](Cp*)3 clusters 1 and 2, respectively, were shown to be intermediates in the formation of an inseparable composite of the closely related clusters [Cu7Al6](Cp*)6 (3), [HCu7Al6](Cp*)6 (3H) and [Cu8Al6](Cp*)6 (4), which just differ by one Cu core atom. The radical nature of the open-shell superatomic [Cu7Al6](Cp*)6 cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu8Al6](Cp*)6 (4), and as well by its ability to undergo σ(C-H) and σ(Si-H) activation reactions of C6H5CH3 (toluene) and (TMS)3SiH (TMS = tris(trimethylsilyl)).

Hydride-encapsulated bimetallic clusters supported by 1,1-dithiolates

A four-coordinated hydride lying at the center of heptanuclear bimetallic clusters was anisotropically refined to convergence by X-ray crystallography.

Isolation of an unusual [Cu6] nanocluster through sequential addition of copper(i) to a polynucleating ligand

Addition of 2 equiv. of CuI to a [Cu]₄ multimetallic complex results in cluster formation leading to the isolation of a rare bicapped tetrahedral [Cu₆I₂] cluster that is stabilised by two conformationally constrained polynucleating ligands.

Coinage Metal Hydrides: Synthesis, Characterization, and Reactivity

Hydride complexes of copper, silver, and gold encompass a broad array of structures, and their distinctive reactivity has enabled dramatic recent advances in synthesis and catalysis. This Review summarizes the synthesis, characterization, and key stoichiometric reactions of isolable or observable coinage metal hydrides. It discusses catalytic processes in which coinage metal hydrides are known or probable intermediates, and presents mechanistic studies of selected catalytic reactions. The purpose of this Review is to convey how developments in coinage metal hydride chemistry have led to new organic transformations, and how developments in catalysis have in turn inspired the synthesis of reactive new complexes.

Polyhydrido Copper Clusters: Synthetic Advances, Structural Diversity, and Nanocluster-to-Nanoparticle Conversion

Metal hydride clusters have historically been studied to unravel their aesthetically pleasing molecular structures and interesting properties, especially toward hydrogen related applications. Central to this work is the hydride ligand, H¯, the smallest closed-shell spherical anion known. Two new developments in polyhydrido nanocluster chemistry include the determination of heretofore unknown hydride coordination modes and novel structural constructs, and conversion from the molecular entities to rhombus-shaped copper nanoparticles (CuNPs). These advances, together with hydrogen evolution and catalysis, have provided both experimentalists and theorists with a rich scientific directive to further explore. The isolation of hexameric [{(Ph3P)CuH}6] (Stryker reagent) could be regarded as the springboard for the recent emergence of polyhydrido copper cluster chemistry due to its utilization in a variety of organic chemical transformations. The stability of clusters of various nuclearity was improved through phosphine, pyridine, and carbene type ligands. Our focus lies with the isolation of novel copper (poly)hydride clusters using mostly the phosphor-1,1-dithiolato type ligands. We found such chalcogen-stabilized clusters to be exceptionally air and moisture stable over a wide range of nuclearities (Cu7 to Cu32). In this Account, we (i) report on state-of-the-art copper hydride cluster chemistry, especially with regards to the diverse and novel structural types generally, and newly discovered hydride coordination modes in particular, (ii) demonstrate the indispensable power of neutron diffraction for the unambiguous assignment and location of hydride ligand(s) within a cluster, and (iii) prove unique transformations that can occur not only between well characterized high nuclearity clusters, but also how such clusters can transform to uniquely shaped nanoparticles of several nanometers in diameter through copper hydride reduction. The increase in the number of low- to high-nuclearity hydride clusters allows for different means by which they can be classified. We chose a classification based on the coordination mode of hydride ligand within the cluster. This includes copper clusters associated with bridging (μ2-H) and capping (μ3-H) hydride modes, followed by an interstitial (μ4-H) hydride mode that was introduced for the first time into octa- and hepta-nuclear copper clusters stabilized by dichalcogen-type ligands. This breakthrough provided a means to explore higher nuclearity polyhydrido nanoclusters, which contain both capping (μ3-H) and interstitial (μ(4-6)-H) hydrides. The presence of bidentate ligands having mixed S/P dative sites led to air- and moisture-stable copper hydride nanoclusters. The formation of rhombus-shaped nanoparticles (CuNPs) from copper polyhydrides in the presence of excess borohydrides suggests the presence of metal hydrides as intermediates during the formation of nanoparticles.

Gas-phase VUV photoionisation and photofragmentation of the silver deuteride nanocluster [Ag10D8L6]2+ (L = bis(diphenylphosphino)methane). A joint experimental and theoretical study

The VUV photoionisation and photofragmentation of a mass-selected, ligated silver deuteride nanocluster was studied.

Accurate yet feasible computations of resonance Raman spectra for metal complexes in solution: [Ru(bpy)3](2+) as a case study

Herein we present a new and promising approach for the high-resolution modeling of vibrational resonance Raman spectra of metal complexes in solution. The model explicitly includes Duschinsky couplings, solvent effects, and anharmonic corrections in a computational tool able to treat large molecular systems containing transition metals.