Highly intense NIR emissive Cu4Pt2 bimetallic clusters featuring Pt(i)-Cu4-Pt(i) sandwich kernel.

Metal nanoclusters (NCs) capable of near-infrared (NIR) photoluminescence (PL) are gaining increasing interest for their potential applications in bioimaging, cell labelling, and phototherapy. However, the limited quantum yield (QY) of NIR emission in metal NCs, especially those emitting beyond 800 nm, hinders their widespread applications. Herein, we present a bright NIR luminescence (PLQY up to 36.7%, ∼830 nm) bimetallic Cu4Pt2 NC, [Cu4Pt2(MeO-C6H5-C[triple bond, length as m-dash]C)4(dppy)4]2+ (dppy = diphenyl-2-pyridylphosphine), with a high yield (up to 67%). Furthermore, by modifying the electronic effects of R in RC[triple bond, length as m-dash]C- (R = MeO-C6H5, F-C6H5, CF3-C6H5, Nap, and Biph), we can effectively modulate phosphorescence properties, including the PLQY, emission wavelength, and excited state decay lifetime. Experimental and computational studies both demonstrate that in addition to the electron effects of substituents, ligand modification enhances luminescence intensity by suppressing non-radiation transitions through intramolecular interactions. Simultaneously, it allows the adjustment of emitting wavelengths by tuning the energy gaps and first excited triplet states through intermolecular interactions of ligand substituents. This study provides a foundation for rational design of the atomic-structures of alloy metal NCs to enhance their PLQY and tailor the PL wavelength of NIR emission.

The interface microenvironment mediates the emission of a semiconductor nanocluster via surface-dopant-involving direct charge transfer.

The interface microenvironment of doped quantum dots (QDs) is crucial in optimizing the properties associated with the photogenerated excitons. However, the imprecision of QDs' surface structures and compositions impedes a thorough understanding of the modulation mechanism caused by the complex interface microenvironment, particularly distinguishing the contribution of surface dopants from inner ones. Herein, we investigated interface-mediated emission using a unique model of an atomically precise chalcogenide semiconductor nanocluster containing uniform near-surface Mn2+ dopants. Significantly, we discovered that Mn2+ ions can directly transfer charges with hydrogen-bonding-bound electron-rich alkylamines with matched molecular configurations and electronic structures at the interface. This work provides a new pathway, the use of atomically precise nanoclusters, for analyzing and enhancing the interface-dependent properties of various doped QDs, including chalcogenides and perovskites.

Alkynyl-Protected Bimetallic Nanoclusters with a Hybrid Mackay Icosahedral Ag42 Cu12 Cl Kernel and an Octahedral Ag22 Cu12 Kernel.

A facile strategy that directly reduces alkynyl-silver precursors and copper salts for the synthesis of bimetallic nanoclusters using the weak reducing agent Ph2 SiH2 is demonstrated. Two alkynyl-protected concentric-shell nanoclusters, (Ph4 P)2 [Ag22 Cu12 (C≡CR)28 ] and (Ph4 P)3 [Ag42 Cu12 Cl(C≡CR)36 ] (Ag22 Cu12 and Ag42 Cu12 Cl, R=bis(trifluoromethyl)phenyl), were successfully obtained and characterized by single-crystal X-ray diffraction and electro-spray ionization mass spectrometry. For the first time, a hybrid 55-atom two-shell Mackay icosahedron was found in Ag42 Cu12 Cl, which is icosahedral M54 Cl instead of M55 . The incorporation of a chloride in the metal icosahedron contributes to the stability of the cluster from both electronic and geometric aspects. Alkynyl ligands show various binding-modes including linear "RC≡C-Cu-C≡CR" staple motifs.

X-ray photochromism of chalcogenide frameworks linked with metal-amine chelates.

Reported here are two X-ray photochromic metal chalcogenide frameworks, which consist of tetrahedral clusters that are linked by transition-metal amine chelates. They have similar structures, but with different organic amine species, and they exhibit different coloration behavior. The photoinduced electron transfer from the metal chalcogenide clusters to the zinc amine chelates is a key point in accounting for their photochromism. Interestingly, a high-contrast (up to 12.4 times) enhancement of the optoelectronic response is obtained for the title compounds after they are treated by X-ray irradiation.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2 (Ag52, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5 (Ag53, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52 and Ag53 have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

Ultrastable Anti-Acid "Shield" in Layered Silver Coordination Polymers.

Surface passivation technology provides noble-metal materials with limited chemical stability, especially under highly acidic condition. To design effective strategy to enhance stability of noble-metal particles, an understanding of their surface anticorrosion mechanism at the atomic level is desirable by using two-dimensional (2D) noble-metal coordination polymer (CP) as an ideal model for their interfacial region. With the protection of 2-thiobenzimidazole (TBI), we isolated two Ag-based 2D CPs, {Ag14 (TBI)12 X2 }n (S-X, where S denotes sheet and X=Cl or Br). These compounds exhibited excellent chemical stability upon immersion in various common solvents, boiling water, boiling ethanol, 10 % hydrogen peroxide, concentrated acid (12 M HCl), and concentrated alkali (19 M NaOH). Systematic characterization and DFT analyses demonstrate that the superior stability of S-X was attributed to the hydrophobic organic shell and dynamic proton buffer layer acting as a double protective "shield".

Compact accumulation of superatomic silver nanoclusters with an octahedral Ag6 core ligated by trithiane.

Two superatomic solids, a bi-cluster compound, [Ag6(3S)4(OTf)4][Ag6(3S)4(CCtBu)4](OTf)2 [Ag6(0)·Ag6(i)], and a homologous nanocluster, [Ag6(3S)4(tfa)4] (Ag6), have been described here, which are both close-packed in the crystal lattice with the ligation of trithiane. Their aggregation-state-dependent absorption and fluorescence properties could be ascribed to the enhanced intercluster charge-transfer in the crystalline state.

Identification of the Active Species in Bimetallic Cluster Catalyzed Hydrogenation.

Identification of the authentic active species of cluster catalysis is rather challenging, and direct structural evidence is quite valuable and difficult to obtain. Two "isostructural" clusters, Ag25Cu4Cl6(dppb)6(PhC≡C)12(SO3CF3)3 (1) and Ag25Cu4Cl6H8(dppb)6(PhC≡C)12(SO3CF3)3 (2H) (dppb is 1,4-bis(diphenylphosphine)butane), have been successfully isolated and structurally characterized. Both these clusters have a centered icosahedron Ag13 core with the same peripheral composition and structure. The only difference is that 2H has eight hydrides but 1 has none, that is, the kernels are Ag135+ and Ag13H85+ in 1 and 2H, respectively. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction is assessed with the two clusters. Cluster 2H is very active with 100% yield within 2 h, whereas 1 shows a very low conversion (∼8%) under the same conditions. Interestingly, high catalytic activity was observed when 1 was converted to 2H with the oxidation of H2O2 under catalytic conditions. The unprecedented transformation of a reduced nanocluster to an Ag(I)Cu(I) bimetallic cluster compound provides an excellent platform to determine the real active cluster in terms of metal cluster catalysis. The present work presents clear structural evidence that the catalytic performance of metal nanoclusters can be modulated by properly regulating the oxidation state of their constituted metal atoms.

N-Heterocyclic Thione-Protected Ag4 Tetrahedra and Ag8 Cubes Cocrystallized in a Single Crystal.

Polynuclear silver clusters have attracted intensive attention in the academic community owing to their rich physicochemical properties. The development of thione-protected silver clusters has been lagging behind the well-explored thiolate-protected silver-sulfide clusters. Herein, we report two N-heterocyclic thione-protected silver clusters: [Ag4(2-TBI)6(SO4)3]2- (Ag4) and [Br@Ag8(2-TBI)12(SO4)2]3+ (Ag8) (2-TBI = 2-thiobenzimidazol), which cocrystallize to form cluster-based molecular crystals with a CaF2-type structure. The cocrystal shows high thermal stability in air. Notably, the two cluster-based layers are alternately assembled to exhibit a unique k-vector-differential crystallographic arrangement. This work may lay a foundation for synthesis of atomically precise and stable silver clusters using readily available N-heterocyclic thione ligands.

Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters.

Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N'-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu11H3(Tf-dpf)6(OAc)2 (Cu11) with three interfacial µ5-H and [Cu12H3(Tf-dpf)6(OAc)2]·OAc (Cu12) with three interstitial µ6-H. A solvent-triggered reversible interconversion between Cu11 and Cu12 has been observed thanks to the flexibility of Tf-dpf. Cu11 shows high activity in the reduction of 4-nitrophenol to 4-aminophenol, while Cu12 displays very low activity. Deuteration experiments prove that the type of hydride is the key in dictating the catalytic activity, for the interfacial µ5-H species in Cu11 are involved in the catalytic cycle whereas the interstitial µ6-H species in Cu12 are not. This work highlights the role of hydrides with regard to catalytic hydrogenation activity.