Postclustering Dynamic Covalent Modification for Chirality Control and Chiral Sensing

Cluster-based functional materials are appealing, because clusters are well-defined building units that can be rationally incorporated for the tuning of structures and properties. Postclustering modification (PCM) allows for tailoring properties through the structural modification of a cluster with preorganized funtional groups. By introducing aldehydes into a robust gold–silver cluster via a protection–deprotection process, we manage to synthesize a new cluster bearing six reactive sites, which are available for PCM through dynamic covalent imine bonds formation with chiral monoamines. Chirality is transferred from the amine to the gold–silver cluster. The homochirality of the resulted cluster has been confirmed by X-ray structural determination and CD spetroscopy. Intense CD signals make it practical for chiral recognition and <i>ee</i> value determination of chiral monoamines. The strategy of prefunctionalizing of cluster and the concept of PCM open a broader prospect for cluster design and applications

Postclustering Dynamic Covalent Modification for Chirality Control and Chiral Sensing

Cluster-based functional materials are appealing, because clusters are well-defined building units that can be rationally incorporated for the tuning of structures and properties. Postclustering modification (PCM) allows for tailoring properties through the structural modification of a cluster with preorganized funtional groups. By introducing aldehydes into a robust gold–silver cluster via a protection–deprotection process, we manage to synthesize a new cluster bearing six reactive sites, which are available for PCM through dynamic covalent imine bonds formation with chiral monoamines. Chirality is transferred from the amine to the gold–silver cluster. The homochirality of the resulted cluster has been confirmed by X-ray structural determination and CD spetroscopy. Intense CD signals make it practical for chiral recognition and <i>ee</i> value determination of chiral monoamines. The strategy of prefunctionalizing of cluster and the concept of PCM open a broader prospect for cluster design and applications

Au₂₀ Nanocluster Protected by Hemilabile Phosphines

A novel phosphine-protected Au₂₀ nanocluster was isolated through the reduction of Au­(PPhpy₂)Cl by NaBH₄ (PPhpy₂ = bis­(2-pyridyl)-phenylphosphine). Its composition was determined to be [Au₂₀(PPhpy₂)₁₀Cl₄]­Cl₂, and single crystal X-ray structural analysis revealed that the Au₂₀ core can be viewed as being generated from the fusion of two Au₁₁ clusters via sharing two vertices. Optical absorption spectroscopy indicated this Au₂₀ has a large HOMO–LUMO gap (<i>E</i>_g ≈ 2.24 eV). This is the first example of a ligand-protected gold nanocluster with a core generated from incomplete icosahedral Au₁₁ building units

Au₂₀ Nanocluster Protected by Hemilabile Phosphines

A novel phosphine-protected Au₂₀ nanocluster was isolated through the reduction of Au­(PPhpy₂)Cl by NaBH₄ (PPhpy₂ = bis­(2-pyridyl)-phenylphosphine). Its composition was determined to be [Au₂₀(PPhpy₂)₁₀Cl₄]­Cl₂, and single crystal X-ray structural analysis revealed that the Au₂₀ core can be viewed as being generated from the fusion of two Au₁₁ clusters via sharing two vertices. Optical absorption spectroscopy indicated this Au₂₀ has a large HOMO–LUMO gap (<i>E</i>_g ≈ 2.24 eV). This is the first example of a ligand-protected gold nanocluster with a core generated from incomplete icosahedral Au₁₁ building units

Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized Au₈Ag₄ Cluster Compounds

Unprecedented geminal tetraauration of acetonitrile has been realized through C–H activation by Au­(I)–Ag­(I) clusters under mild conditions. The reaction of [OAu₃Ag­(dppy)₃]­(BF₄)₂ (dppy = diphenylphosphino-2-pyridine) (<b>1</b>), AgBF₄, and acetonitrile in the presence of methanol at room temperature resulted in the isolation of the novel cluster [(CCN)₂Au₈Ag₄(dppy)₈(CH₃CN)₂]­(BF₄)₆ (<b>2</b>). The centrosymmetric structure consists of two Au₄Ag₂ motifs stabilized by hemilabile phosphines. Triply deprotonated acetonitrile (CCN^3–) is found in a Au₄Ag environment with the terminal carbon bridging four Au­(I) centers and the nitrogen donor linking a Ag­(I) ion, which is the first example of a μ₅-CCN^3– coordination mode. A concerted metalation/deprotonation process for the C–H activation of acetonitrile that indicates the importance of the oxo ion of the oxonium Au­(I) cluster is proposed. Cluster <b>2</b> emits bright green light in the solid state at room temperature upon UV irradiation

Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized Au₈Ag₄ Cluster Compounds

Unprecedented geminal tetraauration of acetonitrile has been realized through C–H activation by Au­(I)–Ag­(I) clusters under mild conditions. The reaction of [OAu₃Ag­(dppy)₃]­(BF₄)₂ (dppy = diphenylphosphino-2-pyridine) (<b>1</b>), AgBF₄, and acetonitrile in the presence of methanol at room temperature resulted in the isolation of the novel cluster [(CCN)₂Au₈Ag₄(dppy)₈(CH₃CN)₂]­(BF₄)₆ (<b>2</b>). The centrosymmetric structure consists of two Au₄Ag₂ motifs stabilized by hemilabile phosphines. Triply deprotonated acetonitrile (CCN^3–) is found in a Au₄Ag environment with the terminal carbon bridging four Au­(I) centers and the nitrogen donor linking a Ag­(I) ion, which is the first example of a μ₅-CCN^3– coordination mode. A concerted metalation/deprotonation process for the C–H activation of acetonitrile that indicates the importance of the oxo ion of the oxonium Au­(I) cluster is proposed. Cluster <b>2</b> emits bright green light in the solid state at room temperature upon UV irradiation

Solvent Dependent Excited State Behaviors of Luminescent Gold(I)–Silver(I) Cluster with Hypercoordinated Carbon

Polynuclear Au­(I) complexes continues to attract considerable attention because of their bright emissions in the visible wavelength, which hold promise in applications in luminescence, fluorescence sensing, and bioimaging. Despite various spectroscopic investigations on their steady state properties, detailed understanding of the origin of their emissions and excited state relaxations is still lacking. Here, we report femtosecond time-resolved transient absorption experiments combined with quantum chemical calculations on a brightly emissive [Au₆Ag₂(C)­(dppy)₆]­(BF₄)₄ cluster in different solvents. Global analysis on the transient absorption spectra based on a sequential model gives three spectral components: (1) excited state absorption (ESA) of ¹MLCT_Au state (τ = 1–3 ps); (2) ESA of ³MLCT_Au state (τ = 11–40 ps), and (3) ESA of ³MLCT_Ag state (long-lived). By variation of the solvent’s polarity and hydrogen bonding ability, the relative population of the triplet MLCT states and the emission properties can be modulated. Especially in methanol, an additional site specific O–H···π bond is formed between methanol molecules and aromatic rings of ligands, which enhances the ultrafast nonradiative decay from the hydrogen bond stabilized ³MLCT_Au state and reduces the population of the emissive ³MLCT_Ag state. The results presented here about the excited state dynamics of luminescent gold­(I)–silver­(I) cluster allow a deeper insight into the origin of their emissions by monitoring the population of the emissive ³MLCT_Ag state and dark ³MLCT_Au state in different environments

Au₁₉ Nanocluster Featuring a V‑Shaped Alkynyl–Gold Motif

A novel Au₁₉ nanocluster with a composition of [Au₁₉(PhCC)₉(Hdppa)₃]­(SbF₆)₂ was synthesized (Hdppa = <i>N</i>,<i>N</i>-bis­(diphenylphosphino)­amine). Single crystal X-ray structural analysis reveals that the cluster comprises a centered icosahedral Au₁₃ core hugged by three V-shaped PhCC–Au–CC­(Ph)–Au–CCPh motifs. Such motif is observed for the first time in an alkynyl-protected gold nanocluster. The Au₁₉ cluster shows two main optical-absorption bands at 1.25 and 2.25 eV, confirmed by time-dependent density functional theory. Orbital analysis indicates that PhCC– groups can actively participate in the frontier orbitals of the whole cluster. The new Au₁₉ cluster and the novel alkynyl–gold motif open the door to understanding the alkynyl–gold interface and discovering many potential members of this new class of gold clusters

Chloride-Promoted Formation of a Bimetallic Nanocluster Au₈₀Ag₃₀ and the Total Structure Determination

We report the total structure determination of a large bimetallic nanocluster with an overall composition of [Au₈₀Ag₃₀(CCPh)₄₂Cl₉]­Cl. It is the largest structurally characterized bimetallic coinage nanocluster so far. The 110 metal atoms are distributed in a concentric four-shell Russian doll arrangement, Au₆@Au₃₅@Ag₃₀Au₁₈@Au₂₁. There are 42 PhCC ligands and 9 μ₂-chloride ligands clamping on the cluster surface. The chloride is proven to be critical for the formation of this giant cluster, as the control experiment in the absence of halide gives only smaller species. This work demonstrates that the halide can play a key role in the formation of a large metal nanocluster, and the halide effect should be considered in the design and synthesis of metal nanoclusters

[Mn^IIIMn^IV₂Mo₁₄O₅₆]^17–: A Mixed-Valence Meso-Polyoxometalate Anion Encapsulated by a 64-Nuclearity Silver Cluster

A 64-nuclearity silver cluster encapsulating a unique POM anion [Mn^IIIMn^IV₂Mo₁₄O₅₆]^17– has been synthesized. The formation of the templating core performs a reassembly process for increasing nuclearities from {MnMo₉} to {Mn₃Mo₁₄}. It represents a rare inorganic meso anion containing mixed-valent Mn that is built up by d-{Mn^IVMo₇} and l-{Mn^IVMo₇} units connecting together through a {Mn^III} fragment