Extra Silver Atom Triggers Room‐Temperature Photoluminescence in Atomically Precise Radarlike Silver Clusters

Luminescent metal clusters show promise for applications in imaging and sensing. However, promoting emission from metal clusters at room temperature is a challenging task owing to the lack of an efficient approach to suppress the nonradiative decay process in metal cores. We report herein that the addition of a silver atom into a metal interstice of the radarlike thiolated silver cluster [Ag₂₇(S^tBu)₁₄(S)₂(CF₃COO)₉(DMAc)₄]?DMAc ( NC1 , DMAc=dimethylacetamide), which is non‐emissive under ambient conditions, produced another silver cluster [Ag₂₈(AdmS)₁₄(S)₂(CF₃COO)₁₀(H₂O)₄] ( NC2 ) that displayed bright green room‐temperature photoluminescence aided by the new ligand 1‐adamantanethiol (AdmSH). The 28th Ag atom, which hardly affects the geometrical and electronic structures of the Ag–S skeleton, triggered the emission of green light as a result of the rigidity of the cluster structure.     

Temperature‐programmed reduction of silver(I) oxide using a titania‐supported silver catalyst under a H2 atmosphere

Reduction kinetics of silver(I) oxide using a titania‐supported silver catalyst was analyzed using temperature‐programmed reduction (TPR) with hydrogen as a reducing gas. Ag₂O reduction to Ag was observed in all samples as a single reduction step occurring at two reduction peaks. Observation of these reduction peaks indicates the existence of different lattice oxygen species, that is, surface and bulk, which are, respectively, attributed to surficial and pore‐deposited Ag₂O aggregates. The powdered samples exhibited high reducibility with average final oxidation states ranging from 0 to +0.18. The apparent activation energies for Ag₂O reduction to Ag metal were 73.35 and 81.71 kJ/mol for surficial and pore‐deposited Ag₂O aggregates, respectively. In this study, a unimolecular decay model was reported to accurately describe the reduction mechanism of Ag/TiO₂ catalysts. Hence, this would also infer that the catalyst reduction is rate‐limited by the nucleation of Ag metal instead of the topochemical reaction and the diffusion of hydrogen and oxygen molecules.     

Atomically Precise Multimetallic Semiconductive Nanoclusters with Optical Limiting Effects

For the first time, multinuclear noble‐metal clusters have been successfully stabilized by Ti‐oxo clusters. Two unprecedented Ag₆@Ti₁₆‐oxo nanoclusters with precise atomic structures were prepared and characterized. The octahedral Ag₆ core has strong Ag?Ag bonds (ca. 2.7 Å), and is further stabilized by direct Ag?O?Ti coordination interactions. Moreover, as a result of different acidic/redox conditions in synthesis, the Ag₆ core can adopt diverse geometric configurations inside the Ti₁₆‐O shell. Correspondingly, structural differences greatly influence their optical limiting effects. The transmittance reduction activity of the clusters towards 532 nm laser shows a nearly linear concentration dependence, and can be optimized up to about 43 %. This work not only opens a new direction for multimetallic semiconductive nanoclusters with interesting optical properties, but also provides molecular models for important noble‐metal/TiO₂ heterogeneous materials.     

A grid‐like two‐dimensional AgI coordination polymer: poly[[[μ3‐N′‐(4‐cyanobenzylidene)isonicotinohydrazide]silver(I)] perchlorate]

This study presents new coordinating modes of a Schiff base with three coordinating groups and an interesting two‐dimensional framework based on two types of constructing units. In the title compound, {[Ag(C₁₄H₁₀N₄O)]ClO₄}_n, the Ag^I ion is coordinated by three N atoms and one O atom from three different N′‐(4‐cyanobenzylidene)isonicotinohydrazide (L) ligands, forming a primary distorted square‐planar coordination geometry. Two ligands each bridge two metal centres through one carbonitrile N atom in a monodentate mode and the hydrazide N and O atoms in a bidentate mode to form a small centrosymmetric (2+2)‐Ag₂L₂ ring as a principal constructing unit. The pyridyl N atoms from four ligands in four of these small rings coordinate to Ag atoms in adjacent rings to form a large hexanuclear silver grid. A two‐dimensional framework of rectangular grids is constructed from these small rings and large grids. Two perchlorate anions are located in each large grid and are bound to the grid by N—H...O hydrogen bonding. Crosslinking between the layers is achieved through long Ag...O interactions between the perchlorate anions and Ag atoms in adjacent layers.     

Crystal Structure of ϵ‐Ag7+xMg26–x – A Binary Alloy Phase of the Mackay Cluster Type

The binary alloy phase ϵ‐Ag_7+xMg_26–x with x ≈ 1 and small amounts of the β′‐AgMg phase crystallize by annealing of Ag–Mg alloys with starting compositions between 24–28 At‐% Ag at 390 to 420 °C. A model structure for the ϵ‐phase consisting of a fcc packing of Mackay clusters was derived from the known structure of the ϵ′‐Ag₁₇Mg₅₄ phase. Crystals of the ϵ‐phase were obtained by direct melting of the elements and annealing. The examination of a single crystal yielded a face‐centered cubic unit cell, space group Fm3 with a = 1761.2(5) pm. The refinement was started with the parameters of the model: wR2(all) = 0.0925 for 1093 symmetrically independent reflections. A refinement of the occupancy parameters indicated a partial replacement of silver for magnesium at two metal atom sites, resulting in the final composition ϵ‐Ag_7+xMg_26–x with x = 0.96(2). There are 264 atoms in the unit cell and the calculated density is 3.568 gcm^–3. The topology of the model was confirmed. Mackay icosahedra are located at the lattice points of a face‐centered cubic lattice. Differences between model and refined structure and their effects on the powder patterns are discussed. The new binary structure type of ϵ‐Ag_7+xMg_26–x can be described in terms of the I3‐cluster concept.     

From Metal–Organic Frameworks to Single‐Atom Fe Implanted N‐doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media

It remains highly desired but a great challenge to achieve atomically dispersed metals in high loadings for efficient catalysis. Now porphyrinic metal–organic frameworks (MOFs) have been synthesized based on a novel mixed‐ligand strategy to afford high‐content (1.76 wt %) single‐atom (SA) iron‐implanted N‐doped porous carbon (Fe_SA‐N‐C) via pyrolysis. Thanks to the single‐atom Fe sites, hierarchical pores, oriented mesochannels and high conductivity, the optimized Fe_SA‐N‐C exhibits excellent oxygen reduction activity and stability, surpassing almost all non‐noble‐metal catalysts and state‐of‐the‐art Pt/C, in both alkaline and more challenging acidic media. More far‐reaching, this MOF‐based mixed‐ligand strategy opens a novel avenue to the precise fabrication of efficient single‐atom catalysts.     

Poly[μ7‐sulfanediyldiacetato‐disilver(I)]

In the title coordination polymer, [Ag₂(C₄H₄O₄S)], each Ag^I cation is four‐coordinated by three of the four carboxylate O atoms and the S atom from symmetry‐related sulfanediyldiacetate ligands, thus defining a distorted tetrahedral geometry at the metal centre. The Ag^I cations are bridged by sulfanediyldiacetate groups, leading to a two‐dimensional layer structure. These layers are interconnected via Ag—S bonds to form a three‐dimensional coordination polymer network overall.     

catena‐Poly[[silver(I)‐μ‐[9,10‐bis(1H‐benzimidazol‐1‐ylmethyl)anthracene]‐κ2N3:N3′] bis(nitrato‐κO)silver(I)]

Yellow needle‐shaped crystals of the title compound, {[Ag(C₃₀H₂₂N₄)][Ag(NO₃)₂]}_n, were obtained by the reaction of AgNO₃ and 9,10‐bis(benzimidazol‐1‐ylmethyl)anthracene (L) in a 2:1 ratio. The asymmetric unit consists of two Ag^I cations, one half L ligand and one nitrate anion. One Ag^I cation occupies a crystallographic inversion centre and links two N‐atom donors of two distinct L ligands to form an infinite one‐dimensional coordination polymer. The second Ag^I cation lies on a crystallographic twofold axis and is coordinated by two O‐atom donors of two nitrate anions to form an [Ag(NO₃)₂]⁻ counter‐ion. The polymeric chains are linked into a supramolecular framework via weak Ag...O [3.124 (5) Å] and Ag...π (2.982 Å) interactions (π is the centroid of an outer anthracene benzene ring). The π interactions contain two short Ag...C contacts [2.727 (6) and 2.765 (6) Å], which can be considered to define Ag–η²‐anthracene bonding interactions. In comparison with a previously reported binuclear Ag^I complex [Du, Hu, Zhang, Zeng & Bu (2008). CrystEngComm, 10 , 1866–1874], this new one‐dimensional coordination polymer was obtained by changing the metal–ligand ratio during the synthesis.     

Cross‐Linked Polyphosphazene Hollow Nanosphere‐Derived N/P‐Doped Porous Carbon with Single Nonprecious Metal Atoms for the Oxygen Reduction Reaction

Heteroatom‐doped polymers or carbon nanospheres have attracted broad research interest. However, rational synthesis of these nanospheres with controllable properties is still a great challenge. Herein, we develop a template‐free approach to construct cross‐linked polyphosphazene nanospheres with tunable hollow structures. As comonomers, hexachlorocyclotriphosphazene provides N and P atoms, tannic acid can coordinate with metal ions, and the replaceable third comonomer can endow the materials with various properties. After carbonization, N/P‐doped mesoporous carbon nanospheres were obtained with small particle size (≈50 nm) and high surface area (411.60 m² g^?1). Structural characterization confirmed uniform dispersion of the single atom transition metal sites (i.e., Co‐N₂P₂) with N and P dual coordination. Electrochemical measurements and theoretical simulations revealed the oxygen reduction reaction performance. This work provides a solution for fabricating diverse heteroatom‐containing polymer nanospheres and their derived single metal atom doped carbon catalysts.     

Central Doping of a Foreign Atom into the Silver Cluster for Catalytic Conversion of CO2 toward C−C Bond Formation

Clusters with an exact number of atoms are of particular interest in catalysis. Their catalytic behaviors can be potentially altered with the addition or removal of a single atom. Now the effects of doping with a single foreign atom (Au, Pd, and Pt) into the core of an Ag cluster with 25 atoms on the catalytic properties are explored, where the foreign atom is protected by 24 Ag atoms (Au@Ag₂₄, Pd@Ag₂₄, and Pt@Ag₂₄). The central doping of a single atom into the Ag₂₅ cluster has a substantial influence on the catalytic performance in the carboxylation reaction of CO₂ with terminal alkyne through C?C bond formation to produce propiolic acid. These studies reveal that the catalytic properties of the cluster catalysts can be dramatically changed with the subtle alteration by a single atom away from the active sites.     

A novel three‐dimensional AgI coordination polymer based on mixed naphthalene‐1,5‐disulfonate and aminoacetate ligands

The three‐dimensional coordination polymer poly[[bis(μ₃‐2‐aminoacetato)di‐μ‐aqua‐μ₃‐(naphthalene‐1,5‐disulfonato)‐hexasilver(I)] dihydrate], {[Ag₆(C₁₀H₆O₆S₂)(C₂H₄NO₂)₄(H₂O)₂]·2H₂O}_n, based on mixed naphthalene‐1,5‐disulfonate (L1) and 2‐aminoacetate (L2) ligands, contains two Ag^I centres (Ag1 and Ag4) in general positions, and another two (Ag2 and Ag3) on inversion centres. Ag1 is five‐coordinated by three O atoms from one L1 anion, one L2 anion and one water molecule, one N atom from one L2 anion and one Ag^I cation in a distorted trigonal–bipyramidal coordination geometry. Ag2 is surrounded by four O atoms from two L2 anions and two water molecules, and two Ag^I cations in a slightly octahedral coordination geometry. Ag3 is four‐coordinated by two O atoms from two L2 anions and two Ag^I cations in a slightly distorted square geometry, while Ag4 is also four‐coordinated by two O atoms from one L1 and one L2 ligand, one N atom from another L2 anion, and one Ag^I cation, exhibiting a distorted tetrahedral coordination geometry. In the crystal structure, there are two one‐dimensional chains nearly perpendicular to one another (interchain angle = 87.0°). The chains are connected by water molecules to give a two‐dimensional layer, and the layers are further bridged by L1 anions to generate a novel three‐dimensional framework. Moreover, hydrogen‐bonding interactions consolidate the network.     

catena‐Poly­[[(pyridin‐4‐ol‐κN)silver(I)]‐μ‐pyridin‐4‐olato‐κ2N:O]

The title complex, [Ag(C₅H₄NO)(C₅H₅NO)]_n, consists of a polymeric neutral chain involving both a neutral pyridin‐4‐ol ligand and a deprotonated pyridin‐4‐olate monoanion. The Ag^I atom shows a T‐shaped coordination geometry, defined by one N atom of the pyridin‐4‐ol and one O and one N atom of two independent pyridin‐4‐olate bridges; the N—Ag—N moiety is approximately linear. The polymeric chains are connected via strong O—H⋯O hydrogen bonds and offset π–π interactions into a three‐dimensional network.     

A Sodalite‐Type Silver Orthophosphate Cluster in a Globular Silver Nanocluster

The synthesis and structure of a giant 102‐silver‐atom nanocluster (NC) 1 is presented. X‐ray structural analysis reveals that 1 features a multi‐shelled metallic core of Ag₆@Ag₂₄@Ag₆₀@Ag₁₂. An octahedral Ag₆ core is encaged by a truncated octahedral Ag₂₄ shell. The Ag₂₄ shell is composed of a hitherto unknown sodalite‐type silver orthophosphate cluster (SOC) {(Ag₃PO₄)₈}, reminiscent of the Ag₃PO₄ photocatalyst. The SOC is capped by six interstitial sulfur atoms, giving a unique anionic cluster [Ag₆@{(Ag₃PO₄)₈}S₆]^6?, which functions as an intricate polyhedral template with abundant surface O and S atoms guiding the formation of a rare rhombicosidodecahedral Ag₆₀ shell. An array of 6 linear Ag₂ staples further surround this Ag₆₀ shell. [Ag₆@{(Ag₃PO₄)₈}S₆]^6? is an unusual Ag‐based templating anion to induce the assembly of a SOC within silver NC. This finding provides molecular models for bulk Ag₃PO₄, and offers a fresh template strategy for the synthesis of silver NCs with high symmetry.     

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L^?1 Ag(NH₃)₂⁺ solution, to synthesize the den‐Ag/Ti electrode. Binary Ag_xCo_y/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and Ag_xCo_y/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐Ag_xCo_y/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag₃₁Co₆₉/Ti>Ag₃₁Co₆₉/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag₃₁Co₆₉/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm^?2 at ?0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.     

catena‐Poly­[[(di‐2‐pyridyl­amine)­silver(I)]‐μ‐nicotinato] and catena‐poly­[[(di‐2‐pyridyl­amine)silver(I)]‐μ‐2,6‐di­hydroxy­benzoato]

In catena‐poly­[[(di‐2‐pyridyl­amine‐κ²N,N′)silver(I)]‐μ‐nico­tinato‐κ²N:O], [Ag(C₆H₄NO₂)(C₁₀H₉N₃)]_n, the Ag^I atom is tetracoordinated by two N atoms from the di‐2‐pyridyl­amine (BPA) ligand [Ag—N = 2.3785 (18) and 2.3298 (18) Å] and by one N atom and one carboxyl­ate O atom from nicotinate ligands [Ag—N = 2.2827 (15) Å and Ag—O = 2.3636 (14) Å]. Bridging by nicotinate N and O atoms generates a polymeric chain structure, which extends along [100]. The carboxyl O atom not bonded to the Ag atom takes part in an intrachain C—H⋯O hydrogen bond, further stabilizing the chain. Pairs of chains are linked by N—H⋯O hydrogen bonds to generate ribbons. There are no π–π interactions in this complex. In catena‐poly­[[(di‐2‐pyridyl­amine‐κ²N,N′)silver(I)]‐μ‐2,6‐di­hydroxy­benzoato‐κ²O¹:O²], [Ag(C₇H₅O₄)(C₁₀H₉N₃)]_n, the Ag^I atom has a distorted tetrahedral coordination, with three strong bonds to two pyridine N atoms from the BPA ligand [Ag—N = 2.286 (5) and 2.320 (5) Å] and to one carboxyl­ate O atom from the 2,6‐di­hydroxy­benzoate ligand [Ag—O = 2.222 (4) Å]; the fourth, weaker, Ag‐atom coordination is to one of the phenol O atoms [Ag⋯O = 2.703 (4) Å] of an adjacent moiety, and this interaction generates a polymeric chain along [100]. Pairs of chains are linked about inversion centers by N—H⋯O hydrogen bonds to form ribbons, within which there are π–π interactions. The ribbons are linked about inversion centers by pairs of C—H⋯O hydrogen bonds and additional π–π interactions between inversion‐related pairs of 2,6‐di­hydroxy­benzoate ligands to generate a three‐dimensional network.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

Templated Atom‐Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18]− Nanocluster

Synthesis of atom‐precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag₂₄Au(SR)₁₈]^? cluster (SR: thiolate) using a pure [Ag₂₅(SR)₁₈]^? cluster as a template. Conversely, the direct synthesis of Ag₂₄Au cluster leads to a mixture of [Ag_25?xAu_x(SR)₁₈]^?, x=1–8. Mass spectrometry and crystallography of [Ag₂₄Au(SR)₁₈]^? reveal the presence of the Au heteroatom at the Ag₂₅ center, forming Ag₂₄Au. The successful exchange of the central Ag of Ag₂₅ with Au causes perturbations in the Ag₂₅ crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag₂₅ and Ag₂₄Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single‐atom level.     

One‐step Synthesis of AuAg Alloy Nanodots and its Electrochemical Studies towards Nitrobenzene Reduction and Sensing

Efficient, stable, and low‐cost electrocatalysts for the degradation and sensing of environment pollutants are essential components of clean environment monitoring. Here we report, one‐step synthesis and characterization of 1–3 nm diameter sized bi‐metallic AuAg nanodots (NDs) embedded in amine functionalized silicate sol‐gel matrix (SSG) and its electrochemical studies toward nitrobenzene. The SSG was used as a reducing agent as well as stabilizer for the prepared mono‐ and bi‐metallic nanoparticles (NPs). From the HRTEM, STEM‐EDS and XPS analyses, the bi‐metallic AuAg NDs were identified as an alloy and not the mixtures of Au and Ag NPs. Characteristic surface plasmon resonance (SPR) band between the Au and Ag NPs SPR absorption region was noticed for the prepared AuAg NDs. The AuAg alloy NDs with different concentrations of Au and Ag (Au₂₅Ag₇₅, Au₅₀Ag₅₀ and Au₇₅Ag₂₅ NDs) modified electrodes exhibited synergistic electrocatalytic effect than did the Au and Ag NPs towards nitrobenzene reduction and detection. Together with ultra‐small size and exceptional colloidal stability features within these SSG‐AuAg NDs pave convenient way for nanotechnology‐based catalysts development and sensor applications.     

catena‐Poly­[[(nitrato‐κ2O,O′)silver(I)]‐μ‐2,2′‐[1,4‐phenyl­enebis­(methyl­ene­thio)]­bis(5‐methyl‐1,3,4‐thia­diazo­le)‐κ2N3:N3′]

In the title complex, [Ag(NO₃)(C₁₄H₁₄N₄S₄)]_n, the Ag^I atom lies on a twofold axis and shows a distorted tetrahedral coordination, comprised of two N‐atom donors from two thia­diazole groups of separate ligands and two O‐atom donors from one nitrate ligand. Each bis­(thio­ether) ligand also lies on a twofold axis and bridges two adjacent Ag atoms to form an infinite chain along the c axis, with an Ag⋯Ag separation of 11.462 (4) Å. Adjacent one‐dimensional chains are further linked into double‐chain motifs through weak Ag⋯S and π–π stacking interactions.     

A stair‐like two‐dimensional silver(I) coordination polymer of N′‐(3‐cyanobenzylidene)nicotinohydrazide

The structure of the title compound, poly[[[μ₃‐N′‐(3‐cyanobenzylidene)nicotinohydrazide]silver(I)] hexafluoroarsenate], {[Ag(C₁₄H₁₀N₄O)](AsF₆)}_n, at 173 K exhibits a novel stair‐like two‐dimensional layer and a three‐dimensional supramolecular framework through C—H...Ag hydrogen bonds. The Ag^I cation is coordinated by three N atoms and one O atom from N′‐(3‐cyanobenzylidene)nicotinohydrazide (L) ligands, resulting in a distorted tetrahedral coordination geometry. The organic ligand acts as a μ₃‐bridging ligand through the pyridyl and carbonitrile N atoms and deviates from planarity in order to adapt to the coordination geometry. Two ligands bridge two Ag^I cations to construct a small 2+2 Ag₂L₂ ring. Four ligands bridge one Ag^I cation from each of four of these small rings to form a large grid. An interesting stair‐like two‐dimensional (3,6)‐net is formed through Ag^I metal centres acting as three‐connection nodes and through L molecules as tri‐linkage spacers.