Uncommon structural and bonding properties in Ag16B4O10

Ag₁₆B₄O₁₀ has been obtained as a coarse crystalline material via hydrothermal synthesis, and was characterized by X-ray single crystal and powder diffraction, conductivity and magnetic susceptibility measurements, as well as by DFT based theoretical analyses. Neither composition nor crystal structure nor valence electron counts can be fully rationalized by applying known bonding schemes. While the rare cage anion (B₄O₁₀)⁸⁻ is electron precise, and reflects standard bonding properties, the silver ion substructure necessarily has to accommodate eight excess electrons per formula unit, (Ag⁺)₁₆(B³⁺)₄(O²⁻)₁₀ × 8e⁻, rendering the compound sub-valent with respect to silver. However, the phenomena commonly associated with sub-valence metal (partial) structures are not perceptible in this case. Experimentally, the compound has been found to be semiconducting and diamagnetic, ruling out the presence of itinerant electrons; hence the excess electrons have to localize pairwise. However, no pairwise contractions of silver atoms are realized in the structure, thus excluding formation of 2e–2c bonds. Rather, cluster-like aggregates of an approximately tetrahedral shape exist where the Ag–Ag separations are significantly smaller than in elemental silver. The number of these subunits per formula is four, thus matching the required number of sites for pairwise nesting of eight excess electrons. This scenario has been corroborated by computational analyses of the densities of states and electron localization function (ELF), which clearly indicate the presence of an attractor within the shrunken tetrahedral voids in the silver substructure. However, one bonding electron pair of s and p type skeleton electrons per cluster unit is extremely low, and the significant propensity to form and the thermal stability of the title compound suggest d¹⁰–d¹⁰ bonding interactions to strengthen the inter-cluster bonding in a synergistic fashion. With the present state of knowledge, such a particular bonding pattern appears to be a singular feature of the oxide chemistry of silver; however, as indicated by analogous findings in related silver oxides, it is evolving as a general one.

Ag₁₆B₄O₁₀, obtained via hydrothermal synthesis, displays an unprecedented bonding scheme, hosting excess electrons localized pairwise in cluster-like silver subunits.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]¹⁸⁻. The cluster showed unique {Ag₇}⁵⁺-to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Small Gold(I) and Gold(I)–Silver(I) Clusters by C−Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho-metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au₆L₄](X)₂ are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag₂O leads to gold–silver clusters [Au₄Ag₂L₄](X)₂. Oxo-trigold(I) species [Au₃O]⁺ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au₅], [Au₄Ag], and [Au₁₂Ag₄] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.     

Size effects of PtcoreAgshell and AgcorePtshell nanoparticles on their catalytic activity in aqueous solutions

Platinum colloids in an aqueous solution catalyze the reduction of silver ions by hydrogen to form Pt-Ag core-shell bimetallic nanoparticles. In the presence of the silver nanoparticles, Pt^II ions are reduced by hydrogen to form Ag_corePt_shell nanoparticles. The effect of the structure and composition of the nanoparticles on the ability of platinum to catalyze the one-electron reduction of methyl viologen by hydrogen in an aqueous solution was studied. For the Pt_coreAg_shell nanoparticles, an induction period preceding the start of the reaction was found. The thicker the silver shell on platinum, the longer the lag time of the reaction, which is probably due to a decrease in the rate of hydrogen transfer to the platinum core. For the Ag_corePt_shell nanoparticles, the size effect was revealed: at the shell thickness less than 1 nm (～4 atomic layers of platinum), platinum loses the ability to catalyze the reaction. The mechanism of the catalytic process is discussed.     

Metal–ligand Lability and Ligand Mobility Enables Framework Transformation via Ligand Release in a Family of Crystalline 2D Coordination Polymers

A family of seven silver(I)-perfluorocarboxylate-quinoxaline coordination polymers, [Ag₄(O₂CR_F)₄(quin)₄] 1 – 5 (R_F=(CF₂)_n-1CF₃)₄, n=1 to 5); [Ag₄(O₂C(CF₂)₂CO₂)₂(quin)₄] 6 ; [Ag₄(O₂CC₆F₅)₄(quin)₄] 7 (quin=quinoxaline), denoted by composition as 4 : 4 : 4 phases, was synthesised from reaction of the corresponding silver(I) perfluorocarboxylate with excess quinoxaline. Compounds 1 – 7 adopt a common 2D layered structure in which 1D silver-perfluorcarboxylate chains are crosslinked by ditopic quinoxaline ligands. Solid-state reaction upon heating, involving loss of one equivalent of quinoxaline, yielding new crystalline 4 : 4 : 3 phases [Ag₄(O₂C(CF₂)_n-1CF₃)₄(quin)₃]_n ( 8 – 10 , n=1 to 3), was followed in situ by PXRD and TGA studies. Crystal structures were confirmed by direct syntheses and structure determination. The solid-state reaction converting 4 : 4 : 4 to 4 : 4 : 3 phase materials involves cleavage and formation of Ag−N and Ag−O bonds to enable the structural rearrangement. One of the 4 : 4 : 3 phase coordination polymers ( 10 ) shows the remarkably high dielectric constant in the low electric field frequency range.     

Ambient Chemical Fixation of CO2 Using a Robust Ag27 Cluster-Based Two-Dimensional Metal–Organic Framework

Unprecedented double S²⁻ templated Ag₂₇ clusters have been stabilized by 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP-H₂) ligands to afford a robust 2D metal–organic framework ( Ag27-MOF ). This silver cluster-assembled material serves as a highly efficient heterogeneous catalyst for the cyclization of both terminal and internal propargylamines with CO₂ under atmospheric pressure. Density functional theory (DFT) calculations illustrate that the high catalytic activity and broad substrate scope are attributable to the saddle-shaped metallic node in Ag27-MOF , which features an accessible platform with high-density silver atoms as π-Lewis acid sites for activating C≡C triple bonds. As a result, different sterically hindered alkyne substrates can be effectively activated through π-interactions with these cationic silver centers.     

Anodic silver (II) oxides investigated by combined electrochemistry,ex situ XPS and in situ X‐ray absorption spectroscopy

Silver (II) oxide layers (AgO) were prepared by anodic oxidation of pre‐oxidized, Ag₂O‐covered silver electrodes in 1 M NaOH (pH 13.8). The oxidized electrodes were investigated using a combination of electrochemical techniques, ex situ X‐ray photoelectron spectroscopy (XPS) and in situ surface‐sensitive grazing incidence X‐ray absorption spectroscopy (EXAFS) under full potential control. The application of these different techniques leads to a detailed, consistent picture of the anodic silver (II) oxide layer formation. The experiments have shown that the chemical composition of the AgO layer varies significantly with oxidation potential, revealing a decreasing oxygen deficiency with increasing anodization potential and oxidation time. XPS as well as EXAFS experiments support the interpretation of the oxide as a mixed valence Ag ⁺ Ag^{3 +} O₂ with different contributions of Ag ⁺ and Ag^{3 +} species, depending on potential and anodization time. Copyright © 2009 John Wiley & Sons, Ltd.     

The size effect in the catalytic activity of AgcorePtshell nanoparticles

It has been shown that, in the presence of 6.3-nm silver nanoparticles, platinum is reduced in a K₂PtCl₄-containing aqueous solution after it is saturated with hydrogen. The process yields bimetallic Ag_corePt_shell “core/shell” nanoparticles. Nanoparticles have been synthesized with different silver-to-platinum molar ratios from 9: 1 to 1: 9. Optical spectroscopy, electron microscopy, and electron diffraction data have confirmed the formation of the core/shell nanoparticles. Bimetallic Ag_corePt_shell nanoparticles exhibit the ability to catalyze the reduction of methyl viologen with hydrogen in an alkaline aqueous solution, which is typical of platinum nanoparticles. The existence of a “critical” thickness of the platinum shell below which the catalytic reduction of methyl viologen does not take place has been established. The critical thickness is about 1 nm, which corresponds to approximately two atomic platinum layers on a silver core.     

Theoretical study of the geometry and electronic structure of the trinuclear [AunAgm (HNCOH)3] (m + n = 3) complex

The structures and properties of different gold and silver mixed-metal trinuclear complexes, [Au_nAg_m(HNCOH)₃] (m + n = 3), were investigated theoretically. The computed properties were compared with those of the [Au₃(HNCOH)₃] complex. The geometries of all complexes were optimized at the B3LYP level of theory using the GEN basis set. The optimization results revealed that the most stable structures of pure Au and Ag complexes are almost similar. In addition, all complexes are flat and highly symmetric. It was shown that the silver substitution had a significant influence on the electronic properties. The metal–metal distances were in the order of: Au–Au < Au–Ag < Ag–Ag. The ionization potential and hardness were found to be decreased while the electron affinity, HOMO–LUMO gap and chemical potential were found to be increased from the [Au₃(HNCOH)₃] to the [Ag₃(HNCOH)₃] complex. The [Au₃(HNCOH)₃] complex was the least reactive in the studied series with the electronic chemical potential equal to −3.98 eV. On the other hand, the value of the chemical potential characterizing the most reactive complex, [Ag₃(HNCOH)₃], was −3.80 eV.     

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.     

A Novel Ag3PO4/Ag/Ag2Mo2O7 Nanowire Photocatalyst: Ternary Nanocomposite for Enhanced Photocatalytic Activity

Ag₃PO₄/Ag/Ag₂Mo₂O₇ composite photocatalyst was successfully prepared via an in situ precipitation method. The as-prepared Ag₃PO₄/Ag/Ag₂Mo₂O₇ nanocomposite included Ag₃PO₄ nanoparticles (NPs) as well as Ag NPs assembling on the surface of Ag₂Mo₂O₇ nanowires. Under visible light irradiation (λ > 420 nm), the Ag₃PO₄/Ag/Ag₂Mo₂O₇ composite degraded rhodamine B (Rh B) efficiently and showed much higher photocatalytic efficiency than pure Ag₃PO₄, Ag₂Mo₂O₇, or Ag₃PO₄/Ag₂Mo₂O₇. It was elucidated that the excellent photocatalytic performance of Ag₃PO₄/Ag/Ag₂Mo₂O₇ for the degradation of Rh B under visible light could be ascribed to the high specific surface area, the extended absorption in the visible light region resulting from the Ag₃PO₄/Ag loading, and the efficient separation of photogenerated electrons and holes through the ternary heterostrucure composed of Ag₃PO₄, Ag and Ag₂Mo₂O₇.     

Multicycle chronoamperometry at rotating ring-disc electrode as a method of current separation into partial currents of silver ionization,Ag<Subscript>2</Subscript>O formation and its chemical dissolution in alkaline medium

A method of multicycle chronoamperometry at rotating ring-disc electrode is suggested for experimental separation of the disc polarization current into its components that correspond to the substrate metal ionization, an oxide formation, and the oxide chemical dissolution. The method was validated by the example of the Ag|Ag₂O|OH^?(H₂O) system. At moderate anodic potentials of Ag-disc (0.48–0.51 V), silver active dissolution from open areas of its surface and through film’s pores dominates; the phase-forming current, hence, the current efficiency of this process drops down rapidly. At the potentials of the maximum at voltammograms (0.52–0.53 V), when the silver active dissolution current is suppressed, the phase-forming currents dominate; they exceed the oxide chemical dissolution rate significantly. The Ag₂O film thickness increases rapidly, the current efficiency of the oxide formation process approaches 100% during the entire disc polarization period. The Ag(I)-oxide chemical dissolution rate constant practically does not depend on the anodic phase-formation potential; however, it somewhat varies depending on the oxide film thickness, thus reflecting changes in the film structure and, possibly, chemical composition (from AgOH to Ag₂O).     

Electronic Structure of Silver Oxides Investigated by AgL XANES Spectroscopy

The chemistry of binary and multinary silver oxides spans from subvalent species (with a mean oxidation number for Ag smaller than + 1) to compounds with Ag in high oxidation states as + 2 and + 3. We have investigated a range of silver oxides, including the binary compounds Ag₂O, AgO, Ag₃O₄ and Ag₂O₃ as well as subvalent ternary oxides, by AgL₃ and AgL₁ XANES spectroscopy. The different valence states of silver are clearly reflected in AgL₃ and AgL₁ XANES spectra. The method thus allows the determination of average oxidation numbers. In addition, the degree of electronic interaction (localized or delocalized electronic states) in silver‐oxygen compounds can be estimated on the basis of AgL₃ XANES spectra.     

Synthesis,crystal structure and studies on the interaction with albumin of a new silver(I) complex based on 2‐(4‐nitrobenzenesulfonamido)benzoic acid

In the present work, the two‐dimensional (2D) polymer poly[[μ₄‐2‐(4‐nitrobenzenesulfonamido)benzoato‐κ⁴O¹:O¹:O^1′:N⁶]silver(I)] (AgL), [Ag(C₁₃H₉N₂O₆S)]_n, was obtained from 2‐(4‐nitrobenzenesulfonamido)benzoic acid (HL), C₁₃H₁₀N₂O₆S. FT–IR, ¹H and ¹³C{¹H} NMR spectroscopic analyses were used to characterize both compounds. The crystal structures of HL and AgL were determined by single‐crystal X‐ray diffraction. In the structure of HL, O—H…O hydrogen bonds between neighbouring molecules result in the formation of dimers, while the silver(I) complex shows polymerization associated with the O atoms of three distinct deprotonated ligands (L^?). Thus, the structure of the Ag complex can be considered as a coordination polymer consisting of a one‐dimensional linear chain, constructed by carboxylate bridging groups, running parallel to the b axis. Neighbouring polymeric chains are further bridged by Ag—C monohapto contacts, resulting in a 2D framework. Fingerprint analysis of the Hirshfeld surfaces show that O…H/H…O hydrogen bonds are responsible for the most significant contacts in the crystal packing of HL and AgL, followed by the H…H and O…C/C…O interactions. The Ag…Ag, Ag…O/O…Ag and Ag…C/C…Ag interactions in the Hirshfeld surface represent 12.1% of the total interactions in the crystal packing. Studies of the interactions of the compounds with human serum albumin (HSA) indicated that both HL and AgL interact with HSA.     

Preparation of Pt<Subscript>core</Subscript>Ag<Subscript>shell</Subscript> nanoparticles: Catalytic reduction of Ag<Superscript>+</Superscript> ions by hydrogen

It is shown that the saturation of an aqueous solution containing silver ions with hydrogen in the presence of 9.5-nm platinum nanoparticles leads to the reduction of silver and the formation of Pt_coreAg_shell bimetal nanoparticles. An increase in the concentration of silver ions gives rise to a number of elementary silver layers that cover the platinum core. It is established that the concentration of silver ions does not substantially affect the rate of the formation of a silver shell on the surface of platinum nanoparticles.     

Discrete Silver(I)‐Palladium(II)‐Oxo Nanoclusters, {Ag4Pd13} and {Ag5Pd15}, and the Role of Metal–Metal Bonding Induced by Cation Confinement

We introduce the class of discrete silver(I)‐palladium(II)‐oxo nanoclusters with the preparation of {Ag₄Pd₁₃} and {Ag₅Pd₁₅}. Both polyanions represent the first examples of noble metal‐capped polyoxo‐noble‐metalates in a fully inorganic assembly, featuring an unprecedented host–guest mode containing hetero‐ and homometallic Ag–Pd and Ag–Ag bonding interactions. Comprehensive theoretical calculations suggest that the Ag–Pd metallic bonds originate partially from surface confinement of Ag^I guest ions onto the anionic polyoxopalladate host that is induced by strong electrostatic forces. This work opens the field of fully inorganic silver‐palladium‐oxo nanoclusters, which can be considered as discrete mixed noble metal precursors for the formation of monodisperse core–shell nanoparticles, with high relevance for catalysis.     

Reactivity in The Solid State Between Ag2S and Ag2CrO4

Reactivity, in the solid state between Ag₂S and Ag₂CrO₄, was investigated by DTA, XRD and IR methods. It was found that, according to a composition of an initial Ag₂S/Ag₂CrO₄ mixture, the products of a reaction of Ag₂S with Ag₂ CrO₄ can be: solid solution with Ag₂CrO₄ structure (Ag₂Cr_1–xS_xO₄) and AgCrO₂; or solid solution Ag₂Cr_1–xS_xO₄, Ag₂SO₄, AgCrO₂ and metallic silver; or Ag₂S, β-Ag₈S₄O₄, Ag, AgCrO₂, Ag₂SO₄ and Ag₂Cr_1–xS_xO₄ solid solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micro-Raman Spectroscopy of Nanostructured Silver Sulfide

Nanostructured silver sulfide powder with an average particle size of about 45 nm, an acanthite α-Ag₂S monoclinic structure (space group P2₁/c), and nonstoichiometric composition Ag_1.93S has been synthesized by the chemical deposition method. The silver sulfide nanopowder has been studied by Raman spectroscopy. According to the Raman scattering data, heating the nanopowder with high-power laser radiation in air leads to photoinduced decomposition of the Ag_1.93S nanopowder to give silver metal. The Raman spectrum of the silver sulfide nanopowder shows a series of bands in the low-frequency range from 90 to 260 cm^–1 associated with vibrations of silver atoms, Ag–S bonds, and symmetric Ag–S–Ag longitudinal modes. Raman spectroscopy confirmed an acanthite monoclinic structure of synthesized silver sulfide nanopowder.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face‐centered‐cubic‐type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]^18?. The cluster showed unique {Ag₇}⁵⁺‐to‐POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.