Superatomic Clusters Research Articles

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.

Zintl based superatom P7M2 (M=Li, Na, K & Be, Mg, Ca) clusters with excellent second and third-order nonlinear optical response

We report geometric, electronic, and NLO properties of designed zintl superatom P7M2 (M = Li, Na, K & Be, Mg, Ca) clusters in which zintl core P7 is substituted with alkali and alkaline earth metals. The studied superatom clusters show excellent thermal and electronic stabilities and their binding energies pe atom range from −21.54 to −95.93 kcal mol−1. The NBO charge analysis reveals excellent charge separation within the clusters, where the charge is transferred from metals to phosphorus atoms. Furthermore, HOMO-LUMO gaps are significantly reduced which illustrates better electronic properties. The calculated first static hyperpolarizability (βo) and second hyperpolarizability (γo) values are up to 282176 × 10−33 and 30869568 × 10−40 esu, respectively. The variational trend and controlling factors for hyperpolarizability (βo) are also estimated by the two-level model study and the values nicely correlate with each other. The highest βtl value of 185423 × 10−33 esu is obtained for P7Mg2 cluster. The obtained significant NLO response for P7Mg2 and P7Ca2 superatom clusters may be attributed to excess electron character. Moreover, to investigate the nonlinearity from the experimental point of view, we carried out hyper Rayleigh scattering (βHRS) measurement where the highest value of 81340.0 × 10−33 esu, is observed for the P7Ca2 superatom cluster. The excellent NLO responses of these zintl superatoms will pave path for further design and synthesis of even better NLO materials.

Alkynyl-Stabilized Superatomic Silver Clusters Showing Circularly Polarized Luminescence.

We report a new enantiomeric pair of superatomic silver clusters, R/S-Ag17, prepared from chiral alkynyl ligands. R-Ag17 and S-Ag17 possess C3 symmetry and emit near-infrared (NIR) light with a quantum yield (QY) of 8.0% under ambient condition as well as NIR circularly polarized luminescence (CPL) as a result of the chirality of the excited states. Both experiments and theoretical calculations indicate for the first time that the CPL originates from transitions between superatomic 1Pz (along the C3 axis) and 1S orbitals. This work opens a new avenue for CPL-active metal nanoclusters by utilizing chiral alkynyl ligands and enlightens the chirality transfer from chiral protecting ligands to superatomic states in metal clusters.

Tuning the Electronic Structure of Atomically Precise Sn/Co/Se Nanoclusters via Redox Matching of Tin(IV) Surface Sites.

A new strategy is reported to tailor the electronic properties of a superatomic metal chalcogenide cluster by redox matching the cluster core with surface tin(IV) sites. Two ternary clusters (SnR2)3Co6Se8L6 (R = Me, nBu) are synthesized by salt metathesis from the hexalithiated salt [Li2(py)2]3Co6Se8L6 and R2SnCl2. Cyclic and differential-pulse voltammetry studies reveal that the tristannylated clusters feature two new, near-degenerate, electronic states within the highest occupied molecular orbital-lowest unoccupied molecular orbital gap of the Co6Se8 core, which are attributed to the reduction of a surface tin site. Single-crystal X-ray diffraction analysis reveals that no Sn···Se coordination is present in the solid state. The single-crystal X-ray structure of the hexalithiated salt starting material is reported for the tetrahydrofuran (THF) adduct variant [Li2(THF)2]6Co6Se8L6.

Chiral Superatomic Nanoclusters Ag47 Induced by the Ligation of Amino Acids

AbstractSilver nanoclusters containing Ag0 atoms protected by amino acids were synthesized and characterized. Chiral superatomic silver nanoclusters [Ag47L12(C≡CtBu)16]BF4 (L=l‐/d‐valine or l‐/d‐isoleucine) have been prepared by reducing AgC≡CtBu and amino acids (AAs) with NaBH4. Single crystal X‐ray diffraction revealed that these clusters have T symmetry, and the Ag47 metal kernel can be viewed as a tetracapped truncated tetrahedron (Ag17) surrounded with six W‐shaped Ag5 units. The clusters are homochiral as evidenced by CD measurements. As for the strong CD signals, large contributions are found from the occupied Ag s,p states (superatomic D states) near the Fermi level. Electron counting revealed that these clusters are 18‐electron systems, suggesting they are superatomic clusters. The superatomic nature with a 1S21P61D10 configuration was supported by DFT calculations. This work paves the way of taking AAs as facile chiral induction agents for the synthesis of metal nanoclusters.

Chiral Superatomic Nanoclusters Ag47 Induced by the Ligation of Amino Acids.

Silver nanoclusters containing Ag0 atoms protected by amino acids were synthesized and characterized. Chiral superatomic silver nanoclusters [Ag47 L12 (C≡Ct Bu)16 ]BF4 (L=l-/d-valine or l-/d-isoleucine) have been prepared by reducing AgC≡Ct Bu and amino acids (AAs) with NaBH4 . Single crystal X-ray diffraction revealed that these clusters have T symmetry, and the Ag47 metal kernel can be viewed as a tetracapped truncated tetrahedron (Ag17 ) surrounded with six W-shaped Ag5 units. The clusters are homochiral as evidenced by CD measurements. As for the strong CD signals, large contributions are found from the occupied Ag s,p states (superatomic D states) near the Fermi level. Electron counting revealed that these clusters are 18-electron systems, suggesting they are superatomic clusters. The superatomic nature with a 1S2 1P6 1D10 configuration was supported by DFT calculations. This work paves the way of taking AAs as facile chiral induction agents for the synthesis of metal nanoclusters.

Transition metal-doped Bn (n = 7−10) clusters: confirmation of a circular disk Jellium model

Using a genetic algorithm combined with density functional theory calculations, we have performed a systematic global search for the low-lying structures of 4d and 5d transition metal (M)-doped Bn clusters with n = 7–10. Diverse structural patterns have been identified as the ground state for MBn clusters, i.e., half-sandwich for early transition metal dopants, wheel-like configuration for middle transition metal dopants, quasi-planar and umbrella-like structures for late transition metal dopants. Among them, the half-sandwich RhB7, IrB7, RuB8 and OsB8; wheel-like IrB9; and umbrella-like AgB9 and AuB9 clusters have relatively high stability, which are not only stabilized by the closed-shell occupation following a circular disk Jellium model, but also enhanced by aromaticity with the π bonds distributed over the circular disk. Our results not only enrich the family of 2D superatomic clusters but also advance the fundamental understanding of the metal-doped boron clusters.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision. Herein, we report a systematic study o...

A new reductant in gold cluster chemistry gives a superatomic gold gallium cluster.

The low valent gallium(i) compound GaCp was primarily used in gold cluster chemistry to synthesize the superatomic cluster [(PPh3)8Au9GaCl2]2+, complementing the borane-dominated set of reducing agents in gold chemistry, opening a whole new field for further research. Using density functional theory calculations, the cluster can be described by the jellium model as an 8-electron superatom cluster.

Influence of nuclear spins on electron spin coherence in isolated, p-doped tin clusters

Magnetic double deflection experiments reveal that nuclear spins diminish electron spin coherence in isolated AlSn12 clusters. A temperature-dependent fraction of the endohedral cage clusters show superatomic response in Stern-Gerlach experiments which allows one to detect spin flips under controlled conditions in a double deflection arrangement. The concentration of nuclear spins in the tin cage is varied by using isotopically enriched tin samples. Hyperfine interaction, nuclear spin statistics and spin dynamics are discussed in detail. It is demonstrated that state-interference in the multistate Landau-Zener system AlSn12 explains why the spin decoherence is significantly increased when one or two nuclear spins are already present in the cluster, while the spin coherence no longer changes significantly with the addition of further nuclear spins.

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(tBuCC)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(tBuCC)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.

Total structural determination of alloyed Au15.37Cu16.63(S-Adm)20 nanoclusters with double superatomic chains.

Thiolated-alloy nanocluster Au15.37Cu16.63(S-Adm)20 ((AuCu)32 for short) has been synthesized. Single crystal X-ray crystallography (SC-XRD) proved that this cluster contains a Au14Cu6 core, which is composed of double superatom chains, two M4(SR)5 (M = Au/Cu) motifs, four Cu(SR)2 monomer staples and two SR molecules at the waist. The composition of this nanocluster is confirmed by SC-XRD and further verified by XPS, EDX and 2H-NMR. Surprisingly, double superatom chains connect to each other only via two Au-Au bonds, which makes the kernel resemble a tunnel. Combined with DFT calculation and electronic structure analysis, it is further proved that the (AuCu)32 nanocluster contains six 2e alloy superatomic Au3Cu2+ units. This work is the first report showing that superatom units (CuAu32+) self-assembling to a hollow kernel maintain the superatom characteristic of metal nanoclusters, which enriches the fundamental knowledge of metal superatom clusters. The stable electronic structure of the nanocluster provides an experimental basis for theoretical analysis in the future. In addition, the hollow structure may be promising in catalytic applications.

Luminescence Regulation of Silver‐Thiolate Clusters Protected by 1,2‐Dithiolate‐o‐carborane

Main observation and conclusionEngineering the surface of the metal clusters with the core structure maintained and tuning their luminescence in a wide range is still a challenge in the nanomaterial research. We modified six mono‐pyridyl ligands with different electronic effects (conjugation effect or induction effect) on a superatomic silver cluster [Ag14(C2B10H10S2)6(CH3CN)8] (denoted as Ag14) through in situ site‐specific surface engineering, and obtained the corresponding clusters [Ag14(C2B10H10S2)6(CH3CN)6(L1/L2)2] (denoted as NC‐1, 2, L1/L2 = 4‐acetylpyridine/ 4‐carboxypyridine) and [Ag14(C2B10H10S2)6(L3/L4/L5/L6)8] (denoted as NC‐3, 4, 5, 6, L3/L4/L5/L6 = 4‐phenylpyridine/4‐(1‐naphthyl)pyridine/9‐(4‐pyridine)anthracene/9‐(4‐pyridine)pyrene). Through the modification of the Ag14 cluster, a wide‐range luminescence from blue to red was realized. This work might provide a practical guide for improving the emission performance of metal clusters via surface engineering.

Evolution of all-carboxylate-protected superatomic Ag clusters confined in Ti-organic cages

In this study, the size of the titanium organic cage was controlled to achieve the restricted growth from a single Ag(I) atom (Ag@Ti5) to rare all-carboxylate-protected superatomic Ag cluster (Ag6@Ti6). The classical octahedral Ag64+ cluster with two delocalized electrons (2e) has been encapsulated in a Ti6 organic cage, which shows high stability in air and dimethyformamide (DMF). Furthermore, larger 2e nested double-tetrahedra Ag clusters (Ag86+ and Ag97+) protected using a tetrahedral hollow metalloligand framework (Ag8@Ti4 and Ag9@Ti4) were obtained. Electrospray ionization mass spectrometry (ESI-MS) and density functional theory (DFT) calculations confirmed that there are two delocalized electrons on these small Ag clusters. This study provides a new form of protection for superatomic Ag clusters and provides a feasible strategy for the development of stable Ag clusters.

Structural, electronic, and adsorbed properties of Be-rich nanoalloys: Be Pt (n = 1–10) clusters

The Hume-Rothery alloy phases of the main-group elements are rather rare, of which the phase stability mechanisms are decided by the electronic effects. The intermetallic compound Be-Pt alloy is a member of this family, but structural and electronic characters of them at nanometer scale still remain unclear. In this work, the geometric structures, stabilities and electronic properties of Be n Pt clusters ( n = 1–10) are first investigated using the method combining the genetic algorithm with density function theory (DFT). Benchmark calculations indicate that the PBE-D3 functional is reliable in predicting the energetic sequences of four isomers of Be 4 Pt cluster compared to the high-level coupled cluster method. In general, the most structures of the alloy clusters can be obtained by replacing one beryllium atom in the pure beryllium (Be m , m = 2–11) clusters with a Pt atom. We found that the Be 4 Pt and Be 10 Pt clusters are two very stable 8e/20e superatoms in this series, respectively, where the electronic structure of Pt atom is d 10 . Analyses of electrostatic potential surfaces show that these two clusters have significant σ-holes with most positive potential regions, which can be seen as binding sites with Lewis bases. When a CO molecule is adsorbed on the superatom clusters, the C O stretching frequency has a large red-shift and the bond length is slightly elongated, due to the electrons of the clusters transfer to the anti-bond π orbital of CO. This work gives inferences for further understanding structural characters of the binary alloy from the nanoscale view.

Contrasting Structure and Bonding of a Copper-Rich and a Zinc-Rich Intermetalloid Cu/Zn Cluster.

Reaction of the Cu(I) sources, [Cu5](Mes)5 and [(iDipp)CuOtBu] (Mes = mesityl; iDipp = 1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene) with the Zn(I) complex [Zn2](Cp*)2 leads to a mixture of intermetallic Cu/Zn clusters with a distribution of species that is dependent on the stoichiometric ratio of the reactants, the reaction time, as well as the temperature. Systematic and careful investigation of the product mixtures rendered the isolation of two new clusters possible, i.e., the Zn-rich, red cluster 1, [CuZn10](Cp*)7 = [Cu(ZnZnCp*)3(ZnCp*)4], as well as the Cu-rich, dark-green cluster 2 [Cu10Zn2](Mes)6(Cp*)2. Structure and bonding of these two species was rationalized with the help of density functional theory calculations. Whereas 1 can be viewed as an 18-electron Cu center coordinated to four ZnCp* and three ZnZnCp* one-electron ligands (with some interligand bonding interaction), compound 2 is better to be described as a six-electron superatom cluster. This unusual electron count is associated with a prolate distortion from a spherical superatom structure. This unexpected situation is likely to be associated with the ZnCp* capping units that offer the possibility to strongly bind to the top and the bottom of the cluster in addition to the bridging mesityl ligands stabilizing the Cu core of the cluster.

Superatomic Clusters: Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity (Adv. Mater. 14/2020)

Superatomic Clusters: Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity (Adv. Mater. 14/2020)

Superatomic Au13 clusters ligated by different N-heterocyclic carbenes and their ligand-dependent catalysis, photoluminescence, and proton sensitivity

We report herein a class of superatomic Au13 clusters stabilized by different N-heterocyclic carbenes (NHCs). The clusters show diverse metal surface structures, properties and functions as exemplified by: (1) the first anionic Au13 cluster [Au13(NHC-1)6Br6]-, which has bulky NHC-1 ligands that lead to a rather open metal surface contributing to its high catalytic activity; (2) the tricationic cluster [Au13(NHC-2)5Br2]3+ which has bidentate, benzyl-rich NHC-2 ligands that make it ultra-stable and highly-luminescent, suitable for bio-imaging; and (3) by bearing two pyridyl groups on NHC-3, the dicationic cluster [Au13(NHC-3)9CI3]2+ exhibits reversible and stable visible absorption and solubility responses to protonation/deprotonation cycles, making it a potential pH sensor (NHC-1 = 1,3-diisopropylbenzimidazolin-2-ylidene; NHC-2 = 1,3-bis(1-benzyl-1H-benzimidazol-1-ium-3-yl)propane; NHC-3 = 1,3-bis(picolyl)benzimidazolin-2-ylidene). The study nicely demonstrates the importance of ligands in designing metal nanoclusters with desired functionalities.

Robustness of Superatoms and Their Potential as Building Blocks of Materials: Al13– vs B(CN)4–

Superatomic clusters, due to their unique size- and composition-specific properties, could form the building blocks of a new class of cluster-assembled materials, provided they can retain their str...

Hierarchical nanosheets built from superatomic clusters: properties, exfoliation and single-crystal-to-single-crystal intercalation.

Tuning the properties of atomic crystals in the two-dimensional (2D) limit is synthetically challenging, but critical to unlock their potential in fundamental research and nanotechnology alike. 2D crystals assembled using superatomic blocks could provide a route to encrypt desirable functionality, yet strategies to link the inorganic blocks together in predetermined dimensionality or symmetry are scarce. Here, we describe the synthesis of anisotropic van der Waals crystalline frameworks using the designer superatomic nanocluster Co3(py)3Co6Se8L6 (py = pyridine, L = Ph2PN(Tol)), and ditopic linkers. Post-synthetically, the 3D crystals can be mechanically exfoliated into ultrathin flakes (8 to 60 nm), or intercalated with the redox-active guest tetracyanoethylene in a single-crystal-to-single-crystal transformation. Extensive characterization, including by single crystal X-ray diffraction, reveals how intrinsic features of the nanocluster, such as its structure, chirality, redox-activity and magnetic profile, predetermine key properties of the emerging 2D structures. Within the nanosheets, the strict and unusual stereoselectivity of the nanocluster's Co edges for the low symmetry (α,α,β) isomer gives rise to in-plane structural anisotropy, while the helically chiral nanoclusters self-organize into alternating Δ- and Λ-homochiral rows. The nanocluster's high-spin Co edges, and its rich redox profile make the nanosheets both magnetically and electrochemically active, as revealed by solid state magnetic and cyclic voltammetry studies. The length and flexibility of the ditopic linker was varied, and found to have a secondary effect on the structure and stacking of the nanosheets within the 3D crystals. With these results we introduce a deterministic and versatile synthetic entry to programmable functionality and symmetry in 2D superatomic crystals.