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.

A Silver Nanocluster Assembled by a Superatomic Building Unit.

A unique assembly of a two-electron superatom, [Ag10{S2P(OiPr)2}8], as a primary building unit in the construction of a supramolecule [Ag10{S2P(OiPr)2}8]2(µ-4,4'-bpy) through a 4,4'-bipyridine (4,4'-bpy) linker is reported. This approach is facilitated by an open site in the structure that allows for effective pairing. The assembled structure demonstrates a minimal solvatochromic shift across organic solvents with variable polarities, highlighting the influence of self-assembly on the photophysical properties of silver nanoclusters.

Diselenophosphate Ligands as a Surface Engineering Tool in PdH-Doped Silver Superatomic Nanoclusters.

The first hydride-doped Pd/Ag superatoms stabilized by selenolates are reported: [PdHAg19(dsep)12] [dsep = Se2P(OiPr)2] 1 and [PdHAg20(dsep)12]+ 2. 1 was derived from the targeted transformation of [PdHAg19(dtp)12] [dtp = S2P(OiPr)2] by ligand exchange, whereas 2 was obtained from the addition of trifluoroacetic acid to 1, resulting in a symmetric redistribution of the capping silver atoms. The transformations are all achieved while retaining an 8-electron superatomic configuration. VT-NMR attests to the good stability of the NCs in solution, and single-crystal X-ray diffraction reveals the crucial role that the interstitial hydride plays in directing the position of the capping silver atoms. The total structures are reported alongside their electronic and optical properties. 1 and 2 are phosphorescent with a lifetime of 73 and 84 µs at 77 K, respectively. The first antibacterial activity data for superatomic bimetallic Pd/Ag nanoclusters are also reported.

Hydride Doping Effects on the Structure and Properties of Eight-Electron Rh/Ag Superatoms: The [RhHx@Ag21-x{S2P(OnPr)2}12] (x = 0-2) Series.

Three hitherto unknown eight-electron rhodium/silver alloy nanoclusters, [RhAg21{S2P(OnPr)2}12] (1), [RhHAg20{S2P(OnPr)2}12] (2), and [RhH2Ag19{S2P(OnPr)2}12] (3), have been isolated and fully characterized. Cluster 1 contains a regular Rh@Ag12 icosahedral core, whereas 2 and 3 exhibit distorted RhH@Ag12 and RhH2@Ag12 icosahedral cores. The single-crystal neutron structure of 2 located the encapsulated hydride at the center of an enlarged RhAg3 tetrahedron. A similar position was found by neutron diffraction for one of the hydrides in 3, whereas the other hydride is trigonally coordinated to Rh and an elongated Ag-Ag edge. The solid-state structures of 1-3 possess C1 symmetry due to the asymmetric arrangement of the surrounding capping Ag atoms. Our investigation shows that the insertion of one hydride dopant provokes the elimination of one capping silver atom on the cluster surface, resulting in the general formula [RhHx@Ag21-x{S2P(OnPr)2}12] (x = 0-2), which maintains the same number of cluster electrons as well as neutral charge. Clusters 1-3 exhibit an intense emission band in the NIR region. Contrarily to their PdAg21 and PdHAg20 relatives, the 4d orbitals of the encapsulated heterometal are somewhat involved in the optical processes.

Controlled Shell and Kernel Modifications of Atomically Precise Pd/Ag Superatomic Nanoclusters.

The first 8-electron Pd/Ag superatomic alloys with an interstitial hydride [PdHAg19 (dtp)12 ] (dtp=S2 P(Oi Pr)2 - ) 1 and [PdHAg20 (dtp)12 ]+ 2 are reported. The targeted addition of a single Ag atom to 1 is achieved by the reaction of one equivalent of trifluoroacetic acid, resulting in the formation of 2 in 55 % yield. Further modification of the shell results in the formation of [PdAg21 (dtp)12 ]+ 3 via an internal redox reaction, with the system retaining an 8-electron superatomic configuration. The interstitial hydride in 1 and 2 contributes its 1s1 electron to the superatomic electron count and occupies a PdAg3 tetrahedron. The distributions of isomers corresponding to different dispositions of the outer capping Ag atoms are investigated by multinuclear VT NMR spectroscopy. The emissive state of 3 has a lifetime of 200 µs (λex =448; λem =842), while 1 and 2 are non-emissive. The catalytic reduction of 4-nitrophenol is demonstrated with 1-3 at room temperature.

Superatom Pruning by Diphosphine Ligands as a Chemical Scissor.

A two-electron silver superatom, [Ag6{S2P(OiPr)2}4(dppm)2] (1), was synthesized by adding dppm (bis(diphenylphosphino)methane) into [Ag20{S2P(OiPr)2}12] (8e). It was characterized by single-crystal crystallography, multinuclear NMR spectroscopy, electrospray ionization-mass spectrometry, density functional theory (DFT), and time-dependent DFT calculations. The added dppm ligands, which carry out the nanocluster-to-nanocluster transformation, act as a chemical scissor to prune the nanocluster geometrically from an icosahedron-based Ag20 nanocluster (NC) to an octahedral Ag6 NC and electronically from eight-electron to two-electron. Eventually, dppm was involved in the protective shell to form a new heteroleptic NC. The temperature-dependent NMR spectroscopy confirms its fluxional behavior, showing the fast atomic movement at ambient temperature. Compound 1 exhibits a bright yellow emission under UV irradiation at ambient temperature with a quantum yield of 16.3%. This work demonstrates a new methodology to achieve nanocluster-to-nanocluster transformation via stepwise synthesis.

Hydride-containing 2-Electron Pd/Cu Superatoms as Catalysts for Efficient Electrochemical Hydrogen Evolution.

The first hydride-containing 2-electron palladium/copper alloys, [PdHCu11 {S2 P(Oi Pr)2 }6 (C≡CPh)4 ] (PdHCu11 ) and [PdHCu12 {S2 P(Oi Pr)2 }5 {S2 PO(Oi Pr)} (C≡CPh)4 ] (PdHCu12 ), are synthesized from the reaction of [PdH2 Cu14 {S2 P(Oi Pr)2 }6 (C≡CPh)6 ] (PdH2 Cu14 ) with trifluoroacetic acid (TFA). X-ray diffraction reveals that the PdHCu11 and PdHCu12 kernels consist of a central PdH unit encapsulated within a vertex-missing Cu11 cuboctahedron and complete Cu12 cuboctahedron, respectively. DFT calculations indicate that both PdHCu11 and PdHCu12 can be considered as axially-distorted 2-electron superatoms. PdHCu11 shows excellent HER activity, unprecedented within metal nanoclusters, with an onset potential of -0.05 V (at 10 mA cm-2 ), a Tafel slope of 40 mV dec-1 , and consistent HER activity during 1000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pd site is the key to HER activity and may provide guidelines for correlating catalyst structures and HER activity.

Hydride-Containing Eight-Electron Pt/Ag Superatoms: Structure, Bonding, and Multi-NMR Studies.

Recent reports on hydride-doped noble metal nanoclusters strongly suggest that the encapsulated hydride is a part of the superatom core, but no accurate location of the hydride could be experimentally proved, so far. We report herein a hydride-doped eight-electron platinum/silver alloy nanocluster in which the position of four-coordinated hydride was determined by neutron diffraction for the first time. X-ray structures of [PtHAg19(dtp/desp)12] (dtp = S2P(OnPr)2, 1; dsep = Se2P(OiPr)2, 2) describe a central platinum hydride (PtH) unit encapsulated within a distorted Ag12 icosahedron, the resulting (PtH)@Ag12 core being stabilized by an outer sphere made up of 7 capping silver atoms and 12 dichalcogenolates. Solid-state structures of 1 and 2 differ somewhat in the spatial configuration of their outer spheres, resulting in overall different symmetries, C1 and C3, respectively. Whereas the multi-NMR spectra of 2 in solution at 173 K reveal that the structure of C3 symmetry is the predominant one, 1H and 195Pt NMR spectra of 1 at the same temperature disclose the presence of isomers of both C1 and C3 symmetry. DFT calculations found both isomers to be very close in energy, supporting the fact that they co-exist in solution. They also show that the [PtH@Ag12]5+ kernel can be viewed as a closed-shell superatomic core, the µ4-hydride electron contributing to its eight-electron count. On the other hand, the 1s(H) orbital contributes only moderately to the superatomic orbitals, being mainly involved in the building of a Pt-H bonding electron pair with the 5dz2(Pt) orbital.

Homoleptic Silver-Rich Trimetallic M20 Nanocluster.

Two silver-rich M20 alloy nanoclusters (NCs), [Cu3.5Ag16.5{S2P(OnPr)2}12] (1) and [Cu2.5AuAg16.5{S2P(OnPr)2}12] (2), were synthesized and fully characterized by electrospray ionization mass spectrometry, NMR spectroscopy, and X-ray crystallography. Cluster 2, the first structurally characterized trimetallic M20 NC, was produced by doping one Au atom into a bimetallic M20 NC. Structural analyses showed the preferred positions of Group 11 metals in the yielded M20 NCs. Their antioxidation ability has been investigated, and the time-dependent UV-vis spectrum shows that the presence of CuI atoms in structures 1 and 2 can improve the antioxidant ability.

Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters.

In sharp contrast to surface hydrides, reactivities of interstitial hydrides are difficult to explore. When treated with a metal ion (Cu+ , Ag+ , and Au+ ), the stable CuI dihydride template [Cu11 H2 {S2 P(Oi Pr)2 }6 (C≡CPh)3 ] (H2 Cu11 ) generates surprisingly three very different compounds, namely [CuH2 Cu11 {S2 P(Oi Pr)2 }6 (C≡CPh)3 ]+ (1), [AgH2 Cu14 {S2 P(Oi Pr)2 }6 ((C≡CPh)6 ]+ (2), and [AuCu11 {S2 P(Oi Pr)2 }6 (C≡CPh)3 Cl] (3). Compounds 1 and 2 are both MI species and maintain the same number of hydride ligands as their H2 Cu11 precursor. Neutron diffraction revealed the first time a trigonal-pyramidal hydride coordination mode in the AgCu3 environment of 2. 3 has no hydride and exhibits a mixed-valent [AuCu11 ]10+ metal core, making it a two-electron superatom.

Isolation and Structural Elucidation of 15-Nuclear Copper Dihydride Clusters: An Intermediate in the Formation of a Two-Electron Copper Superatom.

Highly reactive copper-dihydride clusters, [Cu15 (H)2 (S2 CNR2 )6 (C2 Ph)6 ](PF6 ) {R = n Bu (1H ), n Pr (2H ), i Bu (3H )}, are isolated during the reaction of [Cu28 H15 {S2 CNn Bu2 }12 ](PF6 ) with ten equivalents of phenylacetylene. They are found to be intermediates in the formation of the earlier reported two-electron superatom [Cu13 (S2 CNR2 )6 (C2 Ph)4 ]+ . Better yields are obtained by reacting dithiocarbamate sodium salts, [Cu(CH3 CN)4 ](PF6 ), BH4- and phenylacetylene. The presence of two hydrides in the isolated clusters is confirmed by the synthesis and characterization of its deuteride analogue [Cu15 (D)2 (S2 CNR2 )6 (C2 Ph)6 ]+ , and a single-crystal neutron structure of 2H . Structural characterization of 1H reveals a new bicapped icosahedral copper(I) cage encapsulating a linear copper dihydride (CuH2 )- unit. Reaction of 3H with Au(I) salts yields a highly luminescent [AuCu12 (S2 CNi Bu2 )6 (C2 Ph)4 ]+ cluster.

Synthesis and Luminescence Properties of Two-Electron Bimetallic Cu-Ag and Cu-Au Nanoclusters via Copper Hydride Precursors.

The synthesis, structural characteristics, and photophysical properties of luminescent Cu-rich bimetallic superatomic clusters [Au@Cu12(S2CNnPr2)6(C≡CPh)4]+ (1a+), [Au@Cu12{S2P(OR)2}6(C≡CPh)4]+ (2+), (2a+ = iPr; 2b+ = nPr), [Au@Cu12{S2P(C2H4Ph)2}6(C≡CPh)4]+ (2c+), and [Ag@Cu12{S2P(OnPr)2}6(C≡CPh)4]+ (3+) were studied. Compositionally uniform clusters 1+-3+ were isolated from the reaction of dithiolato-stabilized, polyhydrido copper clusters with phenylacetylene in the presence of heterometal salts. By using X-ray diffraction, the structures of 1a+, 2a+, 2b+, and 3+ were able to be determined. ESI-mass spectrometry and elemental analysis confirmed their compositions and purity. The structural characteristics of these clusters are similar with respect to displaying gold (or silver)-centered Cu12 cuboctahedra surrounded by six dithiocarbamate/dithiophosph(in)ate and four alkynyl ligands. The doping of Au and Ag atoms into the polyhydrido copper nanoclusters significantly enhances their PL quantum yields from Ag@Cu12 (0.58%) to Au@Cu12 (55%) at ambient temperature in solution. In addition, the electrochemical properties of the new alloys were investigated by cyclic voltammetry.

Doping effect on the structure and properties of eight-electron silver nanoclusters.

The bimetallic M20 and M21 compounds, {[Cu3Ag17{S2P(OiPr)2}12]0.5 [Cu4Ag16{S2P(OiPr)2}12]0.5} ({[1a]0.5[1b]0.5}) and [Cu4Ag17{S2P(OiPr)2}12](PF6) (2), have been structurally characterized, in which the Cu(I) ions are randomly distributed on the eight outer positions capping the eight-electron [Ag13]5+ core. DFT calculations show that the statistical disorder results from the nearly neutral preference of copper to occupy any of the eight outer positions. Surprisingly, the UV-Vis absorption spectra of the M20 and M21 bimetallic nanoclusters display an almost identical absorption profile as that of their homometallic [Ag20{S2P(OiPr)2}12] and [Ag21{S2P(OiPr)2}12]+ relatives. This is rationalized by TD-DFT calculations, which show that the frontier orbitals of such eight-electron alloys are largely independent from the nature of the capping metal ions. A blue-shifted absorption is observed upon replacing by Au the central Ag atom in 2, forming the trimetallic compound [Cu4AuAg16{S2P(OiPr)2}12](PF6) (3).

A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations.

A decanuclear silver chalcogenide cluster, [Ag10(Se){Se2P(OiPr)2}8] (2) was isolated from a hydride-encapsulated silver diisopropyl diselenophosphates, [Ag7(H){Se2P(OiPr)2}6], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method illustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear bimetallic clusters, [CuxAg10-x(Se){Se2P(OiPr)2}8] (x = 0-7, 3), via heating [CuxAg7-x(H){Se2P(OiPr)2}6] (x = 1-6) at 60 °C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While the crystal 2 revealed two un-identical [Ag10(Se){Se2P(OiPr)2}8] structures in the asymmetric unit, a co-crystal of [Cu3Ag7(Se){Se2P(OiPr)2}8]0.6[Cu4Ag6(Se){Se2P(OiPr)2}8]0.4 ([3a]0.6[3b]0.4) was eventually characterized by single-crystal X-ray diffraction. Even though compositions of 2, [3a]0.6[3b]0.4 and the previous published [Ag10(Se){Se2P(OEt)2}8] (1) are quite similar (10 metals, 1 Se2-, 8 ligands), their metal core arrangements are completely different. These results show that different synthetic methods by using different starting reagents can affect the structure of the resulting products, leading to polymorphism.

A Two-Electron Silver Superatom Isolated from Thermally Induced Internal Redox Reaction of A Silver(I) Hydride.

Rational syntheses under controllable reducing conditions in the preparation of superatoms with cluster electron number not exceeding two are challenging. Herein a dithiolate-stabilized two-electron silver nanocluster, Ag10 {S2 P(Oi Pr)2 }8 (1), is isolated via a self-redox reaction of Ag7 (H){S2 P(Oi Pr)2 }6 without adding extra reducing agents. The metal framework of Ag7 , a bicapped trigonal bipyramid, is highly correlated to that of Ag10 , suggesting Ag7 (H){S2 P(Oi Pr)2 }6 acts as both reducing agent and template in cluster growth. 1 is highly fluorescent at ambient temperature and TD-DFT calculations indicate that the emission is of 1Px →1S nature.

Polyhydrido Copper Nanoclusters with a Hollow Icosahedral Core: [Cu30 H18 {E2 P(OR)2 }12 ] (E=S or Se; R=nPr, iPr or iBu).

Although atomically precise polyhydrido copper nanoclusters are of prime interest for a variety of applications, they have so far remained scarce. Herein, this work describes the synthesis of a dithiophosphate-protected copper(I) hydride-rich nanocluster (NC), [Cu30 H18 {S2 P(OnPr)2 }12 ] (1H ), fully characterized by various spectroscopic methods and single-crystal X-ray diffraction. The X-ray structure of 1H reveals an unprecedented central Cu12 hollow icosahedron. Six faces of this icosahedron are capped by Cu3 triangles, the whole Cu30 core being wrapped by twelve dithiophosphate ligands and the whole cluster has ideal S6 symmetry. The locations of the 18 hydrides in 1H were ascertained by a single-crystal neutron diffraction study. They are composed of three types: capping µ3 -H, interstitial µ4 -H (seesaw) and µ5 -H ligands (square pyramidal), in good agreement with the DFT simulations. The numbers of hydrides and ligand resonances in the 1 H NMR spectrum of 1H are in line with their coordination environment in the solid state, retaining the S6 symmetry in solution. Furthermore, two new Se-protected polyhydrido copper nanoclusters, [Cu30 H18 {Se2 P(OR)2 }12 ] (2H : R=iPr 3H : R=iBu) were synthesized from their sulfur relative 1H via ligand displacement reaction and their X-ray structures feature the exceptional case where both the NC shape and size are fully conserved during the course of ligand exchange. DFT and TD-DFT calculations allow understanding the bonding and optical properties of clusters 1H -3H . In addition, the reaction of 1H with [Pd(PPh3 )2 Cl2 ] in the presence of terminal alkynes led to the formation of new bimetallic Cu-Pd alloy clusters [PdCu14 H2 {S2 P(OnPr)2 }6 (C≡CR)6 ] (4: R=Ph; 5: R=C6 H4 F).

Copper Clusters Containing Hydrides in Trigonal Pyramidal Geometry.

Structurally precise copper hydrides [Cu11H2{S2P(OiPr)2}6(C≡CR)3], R = Ph (1), C6H4F (2), and C6H4OMe (3), were first synthesized from the polyhydrido copper cluster [Cu20H11{S2P(OiPr)2}9] with nine equivalents of terminal alkynes. Later, their isolated yields were significantly improved by direct synthesis from [Cu(CH3CN)4](PF6), [NH4][S2P(OiPr)2], NaBH4, and alkynes along with NEt3 in THF. 1, 2, and 3 were fully characterized by single-crystal X-ray diffraction, ESI-MS, and multinuclear NMR spectroscopy. All three clustershave 11 copper atoms, adopting 3,3,4,4,4-pentacapped trigonal prismatic geometry, with two hydrides inside the Cu11 cage, the position of which was ascertained by a single-crystal neutron diffraction structure of cluster 1 co-crystallized with a [Cu7(H){S2P(OiPr)2}6] (4) cluster. Six dithiophosphate and three alkynyl ligands stabilize the Cu11H2 core in which the two hydrides adopt a trigonal pyramidal coordination mode. This coordination mode is so far unprecedented for hydride. The 1H NMR resonance frequency of the two hydrides appears at 4.8 ppm, a value further confirmed by 2H NMR spectroscopy for their deuteride derivatives [Cu11(D)2{S2P(OiPr)2}6(C≡CR)3]. A DFT investigation allows understanding the bonding within this new type of copper(I) hydrides.

Homoleptic Platinum/Silver Superatoms Protected by Dithiolates: Linear Assemblies of Two and Three Centered Icosahedra Isolobal to Ne2 and I3.

Three bimetallic platinum/silver nanoclusters, PtAg20(dtp)12 (1), Pt2Ag33(dtp)17 (2), and Pt3Ag44(dtp)22 (3) (dtp: dipropyl dithiophosphate), with cluster electron counts of 8, 16, and 22, respectively, were produced via a one-phase coreduction method. Single-crystal X-ray structures reveal that their inner cores can be visualized as consisting of one, two, and three centered icosahedral Pt@Ag12 units, respectively. In 2 and 3, these units are vertex-sharing and are assembled linearly. Intriguingly, the 22-electron alloy (3) is isolobal to the linear triiodide anion, I3-, and represents the first example of a cluster made of three superatoms whose bonding characteristics are similar to those of a triatomic molecular species.

Synthesis of Bimetallic Copper-Rich Nanoclusters Encapsulating a Linear Palladium Dihydride Unit.

The structurally precise Cu-rich hydride nanoclusters [PdCu14 H2 (dtc/dtp)6 (C≡CPh)6 ] (dtc: di-butyldithiocarbamate (1); dtp: di-isopropyl dithiophosphate (2)) were synthesized from the reaction of polyhydrido copper clusters [Cu28 H15 (S2 CNn Bu2 )12 ]+ or [Cu20 H11 {S2 P(Oi Pr)2 }9 ] with phenyl acetylene in the presence of Pd(PPh3 )2 Cl2 . Their structures and compositions were determined by single-crystal X-ray diffraction and the results supported by ESI-mass spectrometry. Hydride positions in 1 were confirmed by single-crystal neutron diffraction. Each hydride is connected to one Pd0 and four CuI atoms in slightly distorted trigonalbipyramidal geometry. The anatomies of clusters 1 and 2 are very similar and DFT calculations allow rationalizing the interactions between the encapsulated [PdH2 ]2- unit and its Cu14 bicapped icosahedral cage. As a result, Pd has the highest coordination number (14) so far recorded.

Hydride-doped coinage metal superatoms and their catalytic applications.

Superatomic constructs have been identified as a critical component of future technologies. The isolation of coinage metal superatoms relies on partially reducing metallic frameworks to accommodate the mixed valent state required to generate a superatom. Controlling this reduction requires careful consideration in reducing the agent, temperature, and the ligand that directs the self-assembly process. Hydride-based reducing agents dominate the synthetic wet chemical routes to coinage metal clusters. However, within this category, a unique subset of superatoms that retain a hydride/s within the nanocluster post-reduction have emerged. These stable constructs have only recently been characterized in the solid state and have highly unique structural features and properties. The difficulty in identifying the position of hydrides in electron-rich metallic constructs requires the combination and correlation of several analytical methods, including ESI-MS, NMR, SCXRD, and DFT. This text highlights the importance of NMR in detecting hydride environments in these superatomic systems. Added to the complexity of these systems is the dual nature of the hydride, which can act as metallic hydrogen in some cases, resulting in entirely different physical properties. This review includes all hydride-doped superatomic nanoclusters emphasizing synthesis, structure, and catalytic potential.