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The atomic structures of self-assembled silicon nanoribbons and magic clusters on Ag(110) substrate have been studied by high-resolution noncontact atomic force microscopy (nc-AFM) and tip-enhanced Raman spectroscopy (TERS). Pentagon-ring structures in Si nanoribbons and clusters have been directly visualized. Moreover, the vibrational fingerprints of individual Si nanoribbon and cluster retrieved by subnanometer resolution TERS confirm the pentagonal nature of both Si nanoribbons and clusters. This work demonstrates that Si pentagon can be an important element in building silicon nanostructures, which may find important applications for future nanoelectronic devices based on silicon. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids (RTILs) can be used as electrosterical stabilizers for nanoparticles without adding stabilizing agents. However, the nanoparticle stability and its mechanisms are still in discussion. We deposited preformed 2 nm ±0.6 nm silver clusters into the ionic liquid C4MIM PF6 using in situ UV/vis absorption to monitor the deposition process. The time- and temperature-dependent cluster aggregation process was studied with ex situ UV/vis absorption spectroscopy analyzed with electrodynamic calculations using generalized Mie theory. On an atomistic level, the sample structure was investigated using EXAFS and a neural network based analysis of XANES. The combination of all methods shows that an aggregation of the original 2 nm clusters without coalescence takes place, which can be controlled or stopped by choosing an appropriate sample temperature. This approach allows the controlled production of chainlike cluster aggregates in RTIL, promising for a number of applications. [ABSTRACT FROM AUTHOR]

Convenient generation of stable superatomic silver clusters and their systematic site-specific tailoring and directional assembly present an enduring and significant challenge. In this work, we prepared a face-centered cubic (fcc) array of Ag14 superatoms protected by face-capping 1,2-dithiolate-o-carborane (C2B10H10S2) ligands, each produced from 1-thiol-o-carborane in crystallization with simultaneous reduction of Ag+ to Ag0. We find that the corner N-donor ligands contribute predominately to the stability and luminescence of the Ag14 superatom. As the first-formed nanocluster [Ag14(C2B10H10S2)6(CH3CN)8]·4CH3CN (NC-1) with labile vertex-coordinated CH3CN ligands is highly unstable, monodendate pyridine ligands were used to replace these CH3CN species site-specifically, giving [Ag14(C2B10H10S2)6(pyridine/p-methylpyridine)8] (NCs-2,3) in gram scale with its core structure intact, which features ultrastability up to 150 °C in air. Moreover, using bidentate N-containing ligands to bridge the superatomic Ag14 building blocks, we constructed an unprecedented hierarchical series of 1D-to-3D superatomic silver cluster-assembled materials (SCAM- 1,2,3,4), and SCAM-4 is air-stable up to 220 °C. Furthermore, this series of stable solid-state superatomic-nanocluster materials exhibit tunable dual emission with wide-range thermochromism. The present study constitutes a major step toward the development of ligand-modulation of the structure, stability, assembly, and functionality of superatomic silver nanoclusters. [ABSTRACT FROM AUTHOR]

Conspectus: Interest for functional silver clusters (Ag-CLs) has rapidly grown over years due to large advances in the field of nanoscale fabrication and materials science. The continuous development of strategies to fabricate small-scale silver clusters, together with their interesting physicochemical properties (molecule-like discrete energy levels, for example), make them very attractive for a wide variety of applied research fields, from biotechnology and the environmental sciences to fundamental chemistry and physics. Apart from useful catalytic properties, silver clusters (Agn, n < 10) were recently shown to also exhibit exceptional optical properties. The optical properties and performance of Ag-CLs offer strong potential for their integration into appealing micro(nano)-optoelectronic devices. To date, however, the rational design and directed synthesis of Ag-CLs with specific functionalities has remained elusive. The inability for rational design stems mainly from a lack of understanding of their novel atomic-scale phenomena. This is because accurately studying silver cluster systems at such a scale is hindered by the perturbations introduced during exposure to various experimental probes. For instance, silver possesses a strong tendency to cluster and form ever-larger Ag aggregates while probed with high-energy electron beams and X-ray irradiation. As well, there exists a need to provide a stabilizing environment for which Agnδ+ clusters can persist, setting up a complex interacting guest-host system, as isolated silver clusters are confined within a suitable hosting medium. Fundamental research into Agnδ+ formation mechanisms and their important optical properties is paramount to establishing truly informed synthesis protocols. Over recent years, we have developed several protocols for the ship-in-a-bottle synthesis of highly luminescent Ag-CLs within the microporous interiors of zeolite frameworks. This approach has yielded materials displaying a wide variety of optical properties, offering a spectrum of possible applications, from nano(micro)photonic devices to smart luminescent labels and sensors. The versatility of the Ag-zeolite multicomponent system is directly related to the intrinsic and complex tunability of the system as a whole. There are several key zeolite parameters that confer properties to the clusters, namely, the framework Si/Al ratio, choice of counterbalancing ions, silver loading, and zeolite topology, and cannot be overlooked. This Account is intended to shed light on the current state-of-the-art of luminescent Ag-CLs confined in zeolitic matrices, emphasizing the use of combinatorial approaches to overcome problems associated with the correct characterization and correlation of their structural, electronic, and photoluminescence properties, all to establish the important design principles for developing functional silver-zeolite-based materials. Additionally, examples of emerging applications and future perspectives for functional luminescent Ag-zeolite materials are addressed in this Account. [ABSTRACT FROM AUTHOR]

Geometries and electronic properties of neutral Agn, cationic Agn+, and anionic Agn- silver clusters with n = 2-22 were investigated by density functional theory (DFT) with M06 functional. For neutral clusters, transition from planar to "empty cage" structure occurs at n = 7, "empty cage" to "cage with one Ag atom" at n = 18, and to "cage with two Ag atoms" at n = 22. For lowest-energy Agn clusters, Ag8 and Ag18 show lowest polarizability due to closed-shell valence electron configurations 1S²/1P6 and 1S²/1P6/1D10. High stability of Ag8 is manifested in small dissociation energies of Ag9 to Ag8 plus Ag1 and Ag10 cluster to Ag8 plus Ag2. Cluster Ag20 with configuration 1S²/1P6/1D10/2S² is stable due to low dissociation energy of Ag21 to Ag1 and Ag22 to Ag2. Cationic clusters with even n namely Ag10+ (9 valence electrons), Ag16+ (15 valence electrons), and Ag22+ (21 valence electrons) dissociate to Ag1 and closed-shell Ag9+ (1S²/1P6), Ag15+ (1S²/1D10/2S²) and Ag21+ (1S²/1P6/1D10/2S²). For odd n, Ag11+ and Ag17+ dissociate to Ag2 and closed-shell Ag9+ and Ag15+. For anionic clusters Agn-, cohesion energy Ecoh and binding energy (BE) show maxima at n = 7 and n = 17 due to stable Ag7- and Ag17- clusters. Small Agn- clusters (n = 4-11) with even n (except n = 8) have lower dissociation energy for loss of Ag1 while those with odd n have lower dissociation energy for loss of Ag2. For n = 12-22, all clusters have lower dissociation energy for loss of Ag1. [ABSTRACT FROM AUTHOR]

A highly efficient fluorescence switch system based on a closed bipolar electrode (C-BPE) system was proposed for the first time. Here, Au nanoclusters (Au NCs) were premodified on one pole of the BPE and acted as the fluorescent donor. On the basis of the spectral overlap between the absorbance of electrochromic material-Prussian blue (PB) and the fluorescence spectrum of Au NCs, fluorescence quenching ("off" state) induced by the inner filter effect was observed. Due to the electrochemical reversible redox reaction between PB and Prussian white, switching the polarity of driving voltage could easily achieve the fluorescence recovery of the Au NCs, corresponding to the "on" state. Through the reasonable design of C-BPE and optimization of driving voltage, the on-off ratio of the integrated fluorescence switch was up to 2.7 and a good fatigue resistance while performing 10 on-off cycles was obtained owing to the good stability of Au NCs and the reversible redox feature of PB. The introduction of BPE made the fluorescence switch more simple and controllable compared with the traditional three-electrode system, which will provide a new route for the design of the electrical-stimuli responsive fluorescence switch, especially for the integration of the miniaturized device. [ABSTRACT FROM AUTHOR]

Using density functional theory (DFT) and linear and quadratic response time-dependent DFT, we investigated the structure and optical properties of a silver sulfide cluster with the interesting property of dual emission that was observed when in crystal form but not in solution. Since the dual fluorescence is observed only in the crystal, a supposition of stabilization of a higher-energy excited state by an excimer-like complex was analyzed by calculations for a cluster dimer, formed through π-stacking of aromatic groups bonded to the sulfur atoms. However, because of the complexity of the system, a simple one-dimensional method for dimer optimization, which works moderately well in predicting the red-shifted fluorescence compared to its absorption in a naphthalene dimer, predicts only partially the red shift for the emission energy. Interestingly, calculations of the two-photon absorption (TPA) cross-section on the optimized isolated cluster as well as the crystal structure geometry indicate significant off-resonance TPA. While some materials have significantly larger TPA cross-sections, such a TPA cross-section off-resonance could be useful. The high density of states in the dimer system results in a higher probability for significant resonance enhancement and thus much larger TPA cross-sections. [ABSTRACT FROM AUTHOR]

In the presence of oxidant (Ag[SbF6]) and base, N-ferrocenyl thioamide Fc-NHC(S)CH3 (H-1; Fc = Fe(η5-C5H5)(η5-C5H4)) converts in an unexpected multistep reaction sequence to a novel N,S-heterocyclic ring, which initiates an oligomerization reaction. Key intermediates toward the resulting complicated material are Ag6(1)6 silver clusters of the anionic N,S-chelating ligand 1- and EPR-active piano stool complexes resulting from ring-slipped cyclopentadienyl ligands, as well as electrophilic N-ferrocenyl ketenimine Fc-N-C-CH2 (2) and its ferrocenium cation 2+ formed by hydrosulfide elimination. Mechanistic insight is achieved using X-ray diffraction and mass spectrometry, as well as EPR and NMR spectroscopic studies, combined with DFT calculations. In addition to the fundamental mechanistic insight, the results could have implications for smart oligomers/polymers, heterocycle synthesis, and controlled-release materials. [ABSTRACT FROM AUTHOR]

Geometry, chemical bonding, and aromatic feature of a series of small silver clusters doped by an Sc atom (ScAgn with n = 1-7) were investigated by means of density functional theory calculations. A planar shape is found for ScAgn including n from 4 to 7. The growth mechanism is established for the formation of the hexagonal and heptagonal metallic cycles following increase of the number of Ag atoms. Particularly, both clusters ScAg6- and ScAg7 present a planar cyclic form in which the Sc atom is situated at the central position of the Ag6 and Ag7 cycles. The σ aromaticity is unambiguously demonstrated by the existence of strongly diatropic current flows within the ring in both ScAg6- and ScAg7. The isovalent ScCu7 cluster has a similar ring current characteristic. In the Sc-doped ScAgn clusters, a delocalized bonding pattern is found as a connector between the dopant Sc and the Agn host, as indicated by an ELI_D analysis. [ABSTRACT FROM AUTHOR]

Helium droplets were used to assemble composite metal-molecular clusters. Produced clusters have several hundreds of silver atoms in the core, immersed in a shell consisting of methane, ethylene, or acetylene molecules. The structure of the clusters was studied via infrared spectra of the C-H stretches of the hydrocarbon molecules. The spectra of the clusters containing methane and acetylene show two distinct features due to molecules on the interface with silver core and those in the volume of the neat molecular part of the clusters. The relative intensities of the peaks are in good agreement with the estimates based on the number of the captured particles. Experiments also suggest that selection rules for infrared transitions for molecules adsorbed on metal surfaces are also valid for silver clusters as small as 300 atoms. [ABSTRACT FROM AUTHOR]

The design of ordered arrays of metal nanoclusters such as, for example, two-dimensional cluster-organic frameworks might open a new route toward the development of materials with tailored optical properties. Such systems could serve as plasmonically enhanced light-harvesting materials, sensors, or catalysts. We present here a theoretical approach for the simulation of the optical properties of ordered arrays of metal clusters that is based on the ab initio parametrized Frenkel exciton model. We demonstrate that small atomically precise silver clusters can be assembled in one- and two-dimensional arrays on suitably designed porphyrin templates exhibiting remarkable optical properties. By employing explicit time-dependent density functional theory calculations on smaller homologues, we show that the intrinsic optical properties of metal clusters are largely preserved but undergo J- and H-type excitonic coupling that results in controllable splitting of their excited states. Furthermore, ab initio parametrized Frenkel exciton model calculations allow us to predict an energetic splitting of up to 0.77 eV in extended two-dimensional square arrays and 0.79 eV in tilted square aggregates containing up to 25 cluster-porphyrin subunits. [ABSTRACT FROM AUTHOR]

Two 3d-4d heteropolynuclear clusters with Ag-Zn ratios of 9:2 and 9:4 were stepwise constructed from a robust nonanuclear silver cluster. Their crystal structures consist of a common bucket-shaped [Ag9(mba)9]9- (H2mba = 2-mercaptobenzoic acid) core with different numbers of ZnII connected by different exo-oriented carboxylates. Most fascinating is the observation of emission (~703 nm) in the near-infrared (NIR) region at 300 K that may be compared to the related Ag9Zn3 cluster with aliphatic polyamine as auxiliary ligand that emits from the visible (~580 nm). The shift is associated with the change of ligand field of the 2,2'-bipyridine. The emission intensity and lifetime were dramatically enhanced along with the slight bathochromic shift upon cooling from 300 K to 80 K. The results raise two significant issues: (a) the structural and electronic effects of the secondary metal binding to the metalloligand and the factors influencing the heteropolynuclear cluster assembly and (b) the use of NIR fluorescence, introduced by integrating two luminophores into one heteropolynuclear entity, in detecting free-moving zinc in biological systems both in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Silver clusters develop within DNA strands and become optical chromophores with diverse electronic spectra and wide-ranging emission intensities. These studies consider a specific cluster that absorbs at 400 nm, has low emission, and exclusively develops with single-stranded oligonucleotides. It is also a chameleon-like chromophore that can be transformed into different highly emissive fluorophores. We describe four characteristics of this species and conclude that it is highly oxidized yet also metallic. One, the cluster size was determined via electrospray ionization mass spectrometry. A common silver mass is measured with different oligonucleotides and thereby supports a Ag10 cluster. Two, the cluster charge was determined by mass spectrometry and Ag L3-edge X-ray absorption near-edge structure spectroscopy. Respectively, the conjugate mass and the integrated white-line intensity support a partially oxidized cluster with a +6 and +6.5 charge, respectively. Three, the cluster chirality was gauged by circular dichroism spectroscopy. This chirality changes with the length and sequence of its DNA hosts, and these studies identified a dispersed binding site with ~20 nucleobases. Four, the structure of this complex was investigated via Ag K-edge extended X-ray absorption fine structure spectroscopy. A multishell fitting analysis identified three unique scattering environments with corresponding bond lengths, coordination numbers, and Debye-Waller factors for each. Collectively, these findings support the following conclusion: a Ag10+6 cluster develops within a 20-nucleobase DNA binding site, and this complex segregates into a compact, metal-like silver core that weakly links to an encapsulating silver-DNA shell. We consider different models that account for silver-silver coordination within the core. [ABSTRACT FROM AUTHOR]

With the incorporation of Pd or Pt atoms, thiolated Ag-rich 25-metal-atom nanoclusters were successfully prepared and structurally characterized for the first time. With a composition of [PdAg24(SR)18]2- or [PtAg24(SR)18]2-, the obtained 25-metal-atom nanoclusters have a metal framework structure similar to that of widely investigated Au25(SR)18. In both clusters, a M@Ag12 (M = Pd, Pt) core is capped by six distorted dimeric -RS-Ag-SR-Ag-SR- units. However, the silver-thiolate overlayer gives rise to a geometric chirality at variance to Au25(SR)18. The effect of doping on the electronic structure was studied through measured optical absorption spectra and ab initio analysis. This work demonstrates that modulating electronic structures by transition-metal doping is expected to provide effective means to manipulate electronic, optical, chemical, and catalytic properties of thiolated noble metal nanoclusters. [ABSTRACT FROM AUTHOR]

Metalclusters of silver have attracted recent interest of researchersas a result of their potential in different catalytic applicationsand low cost. However, due to the completely filled d orbital andvery high first ionization potential of the silver atom, the silver-basedcatalysts interact very weakly with the reacting molecules. In thecurrent work, density functional theory calculations were carriedout to investigate the effect of hydrogen atom chemisorption on thereactivity and catalytic properties of inert silver clusters. Ourresults affirm that the hydrogen atom chemisorption leads to enhancementin the binding energy of the adsorbed O2molecule on theinert silver clusters. The increase in the binding energy is alsocharacterized by the decrease in the Ag–O and increase in theO–O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O–Obond length, a significant red shift in the O–O stretchingfrequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbedsilver clusters show low reaction barriers and high heat of formationof the final products for the environmentally important CO oxidationreaction as compared to the parent catalytically inactive clusters.The obtained results were compared with those of the correspondinggold and hydrogen atom chemisorbed gold clusters obtained at the samelevel of theory. It is expected the current computational study willprovide key insights for future advances in the design of efficientnanosilver-based catalysts through the adsorption of a small atomor a ligand. [ABSTRACT FROM AUTHOR]

Metal clustershave been very attractive due to their aestheticstructures and fascinating properties. Different from nanoparticles,each cluster of a macroscopic sample has a well-defined structurewith identical composition, size, and shape. As the disadvantagesof polydispersity are ruled out, informative structure–propertyrelationships of metal clusters can be established. [ABSTRACT FROM AUTHOR]

Silver clusters with ∼10 atoms are molecules, and specific species develop within DNA strands. These molecular metals have sparsely organized electronic states with distinctive visible and nearinfrared spectra that vary with cluster size, oxidation, and shape. These small molecules also act as DNA adducts and coordinate with their DNA hosts. We investigated these characteristics using a specific cluster-DNA conjugate with the goal of developing a sensitive and selective biosensor. The silver cluster has a single violet absorption band (λmax = 400 run), and its single-stranded DNA host has two domains that stabilize this cluster and hybridize with target oligonucleotides. These target analytes transform the weakly emissive violet cluster to a new chromophore with blue-green absorption (λmax = 490 nm) and strong green emission (λmax = 550 nm). Our studies consider the synthesis, cluster size, and DNA structure of the precursor violet cluster-DNA complex- This species preferentially forms with relatively low amounts of Agλ+, high concentrations of the oxidizing agent O2, and DNA strands with ≳20 nucleotides. The resulting aqueous and gaseous forms of this chromophore have 10 silvers that coalesce into a single cluster. This molecule is not only a chromophore but also an adduct that coordinates multiple nucleobases. Large-scale DNA conformational changes are manifested in a 20% smaller hydrodynamic radius and disrupted nucleobase stacking. Multidentate coordination also stabilizes the single-stranded DNA and thereby inhibits hybridization with target complements. These observations suggest that the silver cluster-DNA conjugate acts like a molecular beacon but is distinguished because die cluster chromophore not only sensitively signals target analytes but also stringendy discriminates against analogous competing analytes. [ABSTRACT FROM AUTHOR]

Silver acetylide complex [Ag(ArCC)] n (Ar = 3,5-di-tert-butylphenyl) with unprecedented high solubility in common organic solvents has been designed and synthesized. The high solubility is due to two bulky tert-butyl substituents on the phenyl ring. This feature is significant to construct and isolate single crystals of all-alkynyl-stabilized silver clusters, which are crucial to investigate the intrinsic binding interaction and coordination modes between Ag(I) and ethynide ligands. Crystallization of [Ag(ArCC)] n under various conditions resulted in three high-nuclearity homoleptic silver acetylide clusters, namely, [Ag21(ArCC)20](OH) (1), [Ag16(ArCC)16] (2), and [Ag15(ArCC)15] (3). Complex 1 has a [Ag21] cluster protected by twenty 3,5-di-tert-butyl-phenylethynide ligands. Complexes 2 and 3 have neutral [Ag16] and [Ag15] clusters, respectively. In addition to these homoleptic silver clusters, two new silver acetylides [Ag20(ArCC)16(CH3COO)4] (4) and [Ag22(ArCC)16(NO3)4(CH3CH2OH)4](OH)2 (5) were synthesized. The acetate and nitrate anions in these structures are more like counterions instead of acting as critical building blocks or templates for cluster assembly. These results illustrated the significance of 3,5-di-tert-butyl-phenylethynide ligands in the construction and stabilization of high-nuclearity silver clusters. Analysis of structures of 1-5 revealed several novel coordination modes between Ag(I) and ethynide ligands, which contributed considerably to our knowledge of Ag(I)-ethynide binding interactions. [ABSTRACT FROM AUTHOR]

New homoleptic hexanuclear Ag(I) and heteroleptic trinuclear Cu(I) clusters and a Cu(I) coordination polymer (CP) of the formulas [Ag6(dtc)6] 1, [Cu3I2(dppm)3(dtc)] 2, and [Cu(ttc)I]∞ 3 (dtc = N-methylbenzyl-N-methyl-thiophenedithiocarbamate; dppm = 1,1-bis(diphenylphosphino)methane; and ttc = dimethyltrithiocarbonate) were synthesized and characterized by elemental analysis, IR, UV-vis, ¹H, 13C, and 31P NMR spectroscopies, and their structures were elucidated by X-ray crystallography. The complexes show interesting structures and luminescent properties. Complex 1, which is centrosymmetric, contains four short Ag···Ag interactions at 2 × 2.966(1) and 2 × 3.014(1) Å. There are also several Ag···Ag distances of 3.3-3.4 Å. The molecule shows hexagonal orientation with alternating silver and sulfur atoms of the overlapping Ag3S3 hexagons in the front and rear, along the a axis. Complex 2 is a rare trinuclear cluster complex of Cu(I); the Cu···Cu distances are 2.906(2), 3.551(2), and 3.338(2) Å, the foremost representing a substantial intermetallic contact. The Cu3I2P6S2 core is comprised of three fused distorted hexagonal rings with the I1 atom located at the center participating in all three rings. Complex 3 is an iodide-bridged CP with a "staircase"-like arrangement in which the Cu(I) is tetrahedrally surrounded by a sulfur atom from the ttc ligand and three iodine atoms. Unlike 3, which is nonluminescent, 1 and 2 are strongly luminescent in the solid and solution at room temperature. The time-resolved emission spectra reveal a triexponential decay curve and short mean lifetime characteristic of fluorescence behavior. Diffuse reflectance spectroscopy revealed semiconducting behavior with band gaps of 2.12, 3.01, and 2.18 eV for 1-3, respectively. [ABSTRACT FROM AUTHOR]

We have investigated the gas-phasereactivity of silver clusterswith ethanethiol in a fast-flow tube reactor. The primary clusterproducts observed in this reaction are AgnSH–and AgnSH2–, indicating C–S bond activation, togetherwith interesting byproducts H3S–and(H3S)2–. Agn–clusters with an odd number of valenceelectrons (n= even) were observed to be more reactivethan those with an even number of electronsa feature previouslyonly observed in the reactivity of Agn–with triplet oxygen, indicating that radicalactive sites play a role in their reactivity. Furthermore, the reactivitydramatically increases with large flow rate of ethanethiol being introducedin the flow tube. Theoretical investigations on the reactivity ofAg13–and Ag8–with ethanethiol indicate that both Ag13–and Ag8–face significant barriersto reactivity with a single ethanethiol molecule. However, Ag8–reacts readily in a cooperative reactionwith two ethanethiol molecules, consistent with the dramatic increasein reactivity with a large flow rate. Further hydrogen-transfer reactionsmay then release an ethylene molecule or an ethyl radical resultingin the observed AgnSH–species. [ABSTRACT FROM AUTHOR]

Theelectronic structure of two recently crystallographically solved,thiolate–phosphine protected silver clusters Ag14and Ag16are analyzed via density functional theory (DFT)and their optical excitations are analyzed from time-dependent DFTperturbation theory. Both clusters can be characterized as havingthe S2free-electron configuration in the metal core, whichis the first time such a configuration is confirmed for structurallyknown ligand-protected noble metal clusters. However, their differentcore shapes and ligand layer induce significantly different opticalspectra. Performance of gradient-corrected DFT functionals is discussedand it is shown that the asymptotically correct Leeuwen–BaerendsLB94 functional reproduces the optical spectrum of Ag14in a good agreement with experiment. Choice of the functional becomesimportant for clusters where the optical transitions are dominatedby the electron-rich ligand layer. [ABSTRACT FROM AUTHOR]

Silver clusters with ~10 atoms form within DNA strands, and the conjugates are chemical sensors. The DNA host hybridizes with short oligonucleotides, and the cluster moieties optically respond to these analytes. Our studies focus on how the cluster adducts perturb the structure of their DNA hosts. Our sensor is comprised of an oligonucleotide with two components: a 5'-cluster domain that complexes silver clusters and a 3'-recognition site that hybridizes with a target oligonucleotide. The single-stranded sensor encapsulates an ~11 silver atom cluster with violet absorption at 400 nm and with minimal emission. The recognition site hybridizes with complementary oligonucleotides, and the violet cluster converts to an emissive near-infrared cluster with absorption at 730 nm. Our key finding is that the near-infrared cluster coordinates two of its hybridized hosts. The resulting tertiary structure was investigated using intermolecular and intramolecular variants of the same dimer. The intermolecular dimer assembles in concentrated ( ~5 μM) DNA solutions. Strand stoichiometries and orientations were chromatographically determined using thymine-modified complements that increase the overall conjugate size. The intramolecular dimer develops within a DNA scaffold that is founded on three linked duplexes. The high local cluster concentrations and relative strand arrangements again favor the antiparallel dimer for the near-infrared cluster. When the two monomeric DNA/violet cluster conjugates transform to one dimeric DNA/near-infrared conjugate, the DNA strands accumulate silver. We propose that these correlated changes in DNA structure and silver stoichiometry underlie the violet to near-infrared cluster transformation. [ABSTRACT FROM AUTHOR]

Threenew inorganic coordination polymers, {[Mn(H2O)6][Mn2(H2O)6][(Cu6(mna)6]·6H2O}, 1, {[Mn4(OH)2(H2O)10][(Cu6(mna)6]·8H2O}, 2, and {[Mn2(H2O)5][Ag6(Hmna)2(mna)4]·20H2O}, 3, have been synthesized at room temperaturethrough a sequential crystallization route. In addition, we have alsoprepared and characterized the molecular precursor [Cu6(Hmna)6]. Compounds 1and 3have a two-dimensional structure, whereas 2has a three-dimensional structure. The formation of 2has been achieved by minor modification in the synthetic composition, suggesting the subtle relationship between the reactant compositionand the structure. The hexanuclear copper and silver cluster coreshave Cu···Cu and Ag···Ag distances closeto the sum of the van der Waals radii of Cu1+and Ag1+, respectively. The connectivity between [Cu6(mna)6]6-cluster units andMn2+ions gives rise to a bruciterelatedlayer in 1and a pcu-net in 2. The [Ag6(Hmna)2(mna)4]4-cluster in 3, on the other hand, formsa sql-net with Mn2+. Compound 1exhibits an interesting and reversible hydrochromic behavior, changing from pale yellow to red, on heating at 70 °C or treatment undera vacuum. Electron paramagnetic resonance studies indicate no changein the valence states, suggesting the color change could be due tochanges in the coordination environment only. The magnetic studiesindicate weak antiferromagnetic behavior. Proton conductivity studiesindicate moderate proton migrations in 1and 3. The present study clearly establishes sequential crystallizationas an important pathway for the synthesis of heterometallic coordinationpolymers. [ABSTRACT FROM AUTHOR]

The multinuclear metal–ligandsupramolecular synthon RC6H4CC⊃Agn(R = Me, F; n= 3–5)has been employed toconstruct the two high-nuclearity silver ethynide cluster compounds[(NO3)2@Ag26(o-MeC6H4CC)16](NO3)8·5H2O (1) and [NO3@Ag15(o-FC6H4CC)10](NO3)4(2), which bearthe same nitrate central core. The synthesis of [CrO4@Ag18(iPrCC)12](ClO4)4(3) and [ClO4@Ag18(iPrCC)12](ClO4)5(4) demonstrated the effect of variation ofcentral anionic core size and charge on the construction of multidimensionalorganosilver(I) networks. The bulkiness of the peripheral ligandsand the orientation of substituents with respect to the ethynide groupproved to be dominant factors that direct the formation of high-nuclearityclusters and the assembly of coordination networks. To our knowledge, 1and 2are the first examples using the nitrateanion for templated cluster synthesis. [ABSTRACT FROM AUTHOR]

Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core–shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal–metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications. [ABSTRACT FROM AUTHOR]

The facile syntheses of enantiomeric atomically precise silver clusters starting from achiral ligands remain a substantial challenge to explore. In this work, a pair of atomically precise enantiomers of R / S -[Ag 17 Cl( i PrS) 9 S(CH 3 COO) 5 H 2 O] ( R/S-Ag 17 , i PrS = isopropanethiolate) clusters have been synthesized using a viable solvothermal approach. The chirality of the resulting enantiomeric R/S-Ag 17 clusters is attributed to the asymmetric arrangement of surface achiral ligands. Both R/S-Ag 17 enantiomers could form the two-dimensional (2D) assemblies via intercluster interactions of basic building blocks containing Ag 16 S 8 moieties, i PrS-Ag motifs, and S 2- linkers. Such a small ligand-induced 2D assembly greatly contributes to the enhancement of thermal stability and photocatalytic activity of R/S-Ag 17 clusters, providing possibilities for exploring robust coinage cluster-based assembly with attractive catalytic properties.

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 ee 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. [ABSTRACT FROM AUTHOR]

We have developed a fluorescence turn-on assay using DNA-templated silver nanoclusters (Ag NCs) (i.e., 12 polycytosine-templated silver nanoclusters, dC12-Ag NCs), which is amenable to rapid, ultrasensitive assay of acetylcholinesterase (AChE). The detection mechanism is based on the concept, that is, AChE hydrolyzes the acetylthiocholine (ATCh) chloride to produce thiocholine (TCh). Subsequently, TCh sensitively and rapidly reacts with dC12-Ag NCs via Ag-S bond forming and enhances the fluorescence of dC12-Ag NCs. Using dC12-Ag NCs, detection of TCh has a linear concentration range of 2.0 nM to 16.0 nM and a detection limit of 0.3 nM. Due to the sensitive and rapid fluorescence turn-on response of dC12-Ag NCs to TCh, AChE with activity as low as 0.5 × 10-4 U/mL (signal/noise = 3) can be analyzed with a dynamic range of 0.1 to 1.25 × 10-3 U/mL. The promising application of the proposed method in AChE inhibitor screening was demonstrated. AChE concentrations were determined in human blood red cell (RBC) membranes from clinical specimens using dC12-Ag NCs, and the quantitative results were validated with Ellman's method. Aside from the ease of manufacture, reduction of matrix effect, and low background noise, the continuous detection format and detection sensitivity can open up to wider applications to AChE activity assay in neurobiology, toxicology, and pharmacology, among other fields. [ABSTRACT FROM AUTHOR]

Neutral silver clusters, Agn, werestudied using density functional theory (DFT) followed by high levelcoupled cluster CCSD(T) calculations to determine the low energy isomersfor each cluster size for small clusters. The normalized atomizationenergy, heats of formation, and average bond lengths were calculatedfor each of the different isomeric forms of the silver clusters. For n= 2–6, the preferred geometry is planar, and thelarger n= 7–8 clusters prefer higher symmetry,three-dimensional geometries. The low spin state is predicted to bethe ground state for every cluster size. A number of new low energyisomers for the heptamer and octamer were found. Additional largerAgnstructures, n<100, were initially optimized using a tree growth-hybrid genetic algorithmwith an embedded atom method (EAM) potential. For n≤ 20, DFT was used to optimize the geometries. DFT with benchmarkedfunctionals were used to predict that the normalized atomization energies(⟨AE⟩s) for Agnstart toconverge slowly to the bulk at n= 55. The ⟨AE⟩for Ag99is predicted to be ∼50 kcal/mol. [ABSTRACT FROM AUTHOR]

A water-soluble highly fluorescentsilver cluster on Au(I) surfacehas been synthesized with green chemistry under sunlight. The evolutionof the silver cluster is synergistic, demanding gold and glutathione.The fluorescent Au(I)core–Ag(0)shellparticlesare huge in size and at the same time they are robust. That is whythey become a deliverable fluorescing solid upon drying. Again, thegiant particles run into common water miscible solvents. As a result,the fluorescence intensity increases to a great extent without anyalteration of emission maxima. In this respect, acetone has been foundto be the best-suited solvent. To have a universal applicability ofthe fluorescent clusters, the particles in the water pool of a reversemicelle have been prepared to transfer the particles into differentwater immiscible solvents. The comparatively lower fluorescence intensityof the particles has been ascribed to a space confinement effect.Finally, giant-cluster-impregnated yellow-orange fluorescent polymerfilm and fluorescent cotton wool, as well as paper substrate, havebeen prepared. The antibacterial activity of the fluorescent particlehas also been tested involving modified cotton wool and paper substratefor Gram-negative and -positive Escherichia coliand Staphylococcus aureus, respectively. [ABSTRACT FROM AUTHOR]

We assess the accuracy of severallong-range-corrected (LC-) density functionals for the predictionof absorption spectra of silver clusters by time-dependent densityfunctional theory. Several types of LC-functionals, with the exactHartree–Fock exchange at long-range, are used: those applyingthe long-range correction to a standard GGA-type functional (LC-BP86,LC-ωPBE) or to a local meta-GGA functional(LC-M06L) and two global hybrid functionals (CAM-B3LYP and ωB97x).The spectra calculated with those density functionals are in goodagreement with the recent accurate experimental measurements. We showthat CAM-B3LYP and ωB97x are some of the most accurate functionalsfor evaluating the electronic excitation energies, while LC-M06L ismore effective in reducing the occurrence of spurious states. Thelong-range correction appears to be essential in describing the absorptionspectra of large clusters. The description of the plasmon-like bandwith LC functionals as transitions associated with excitations froms orbitals to s + p orbitals is in fairly good agreement with theclassical interpretation as a collective excitation of valence selectrons. [ABSTRACT FROM AUTHOR]

Molecular silver clusters conjugated with DNA act as analyte sensors. Our studies evaluate a type of cluster-laden DNA strand whose structure and silver stoichiometry change with hybridization. The sensor strand integrates two functions, the 3' region binds target DNA strands through base recognition while the 5' sequence C3AC3AC3TC3A favors formation of a near-infrared absorbing and emitting cluster. This precursor farm exclusively harbors an ~11 silver atom duster that absorbs at 400 nan and that condenses its single-stranded host. The 3' recognition site associates with a complementary target strand, thereby effecting a 330 nm red-shift in cluster absorption and a background-limited recovery of cluster emission at 790 nm. One factor underlying these changes is sensor unfolding and aggregation. Variations in salt and oligonucleotide concentrations control cluster development by influencing DNA association. Structural studies using fluorescence anisotropy, fluorescence correlation spectroscopy, and size exclusion chromatography show that the sensor-cluster conjugate opens and subsequently dimerizes with hybridization. A second factor contributing to the spectral and photophysical changes is duster transformation. Empirical silver stoichiometries are preserved through hybridization, so hybridized, dimeric near-infrared conjugates host twice the amount of silver in relation to their violet absorbing predecessors. These DNA structure and net silver stoichiometry alterations provide insight into how DNA-silver conjugates recognize analyses. [ABSTRACT FROM AUTHOR]

Reactions of Ag(I) salt, NH4(E2P(OR)2) (R = 'Pr, Et; E = Se, S), and NaBH4 in a 7:6:1 ratio in CH2Cl2 at room temperature, led to die formation of hydride-centered heptanuclear silver clusters, [Ag7(H){E2P(OR)2}6] (R = 'Pr, E = Se (3): R = Et; E = S(4). The reaction of [Ag10(E){E2P-(OR)2}8] with NaBH4 in CH2Cl2 produced [Ag8(H){E2P-(OR)2}6](PF6) (R = 'Pr, E = Se (1): R = Et; E = S(2)), which can be converted to clusters 3 and 4, respectively, via the addition of 1 equiv of borohydride. Intriguingly clusters 1 and 2 can be regenerated via adding 1 equiv of Ag(CH3CN)4PF6 to the solution of compounds 3 and 4, respectively. All complexes have been fully characterized by NMR (¹H, 77Se, 109Ag) spectroscopy, UV--vis, electrospray ionization mass spectrometry (ESI-MS), FT-IR, thermogravimetric analysis (TGA), and elemental analysis, and molecular structures of 3H and 4H were clearly established by single crystal X-ray diffraction. Both 3H and 4H exhibit a tricapped tetrahedral Ag7 skeleton, which is inscribed within an E12 icosahedron constituted by six dialkyl dichalcogenophosphate ligands in a tetrametallic-tetraconnective (µ2,µ2) bonding mode. Density functional theory (DFT) calculations on the models [Ag7(H)(E2PH2)6] (E = Se: 3'; E = S: 4') yielded to a tricapped, slightiy elongated tetrahedral silver skeleton, and time-dependent DFT (TDDFT) calculations reproduce satisfyingly the UV--vis spectrum with computed transitions at 452 and 423 nm for 3' and 378 nm for 4'. Intriguingly further reactions of [Ag7(H){E2P(OR)2}6] with 8-fold excess amounts of NaBH4 produced monodisperse silver nanoparticles with an averaged particle size of 30 nm, which are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and UV--vis absorption spectrum. [ABSTRACT FROM AUTHOR]

Control over the electronic state of the Ag3clusteris approached via a progression of ultrafast photoinduced transitionswithin the full electronic manifold of the negative to the neutraland finally the cationic state of the system. High-bandwidth supercontinuumlaser pulses ranging from 500 to 950 nm are employed for addressingthe wide range of electronic resonance conditions associated withthe ladder climbing process of a tandem photoelectron detachment anda resonance enhanced multiphoton ionization (REMPI). With the controlof the phase over the full spectral envelope of the supercontinuumin a pulse shaper arrangement, pulse forms are generated with theaim of synchronizing ultrashort subpulse sequences to the characteristicdynamics of the system during charge reversal. Pulse forms rangingover several hundred femtoseconds in total duration and subpulse structuresdown to 15 fs duration with a variable spectral composition can beobtained for this purpose. A free optimization based on a closed-loopgenetic algorithm is employed for ordering the subpulse sequencesto match the structural evolution of the system. The effective controlattainable in this scenario is evaluated in view of maintaining adefined sequence of electronic transitions within the complex dynamicresponse of the system during the photoexcitation. Further emphasisis made on analyzing the degree of control attainable in the nonlinearregime of multiphoton excitation at supercontinuum bandwidths. [ABSTRACT FROM AUTHOR]

Spin accommodation is demonstrated to play a determining role in the reactivity of silver cluster anions with oxygen. Odd-electron silver clusters are found to be especially reactive, while the anionic 13-atom cluster exhibits unexpected stability against reactivity with oxygen. Theoretical studies show that the odd–even selective behavior is correlated with the excitation needed to activate the O–O bond in O2. Furthermore, by comparison with the reactivity of proximate even-electron clusters, we demonstrate that the inactivity of Ag13- is associated with its large spin excitation energy, ascribed to a crystal-field-like splitting of the orbitals caused by the bilayer atomic structure, which induces a large gap despite not having a magic number of valence electrons. [ABSTRACT FROM AUTHOR]

We show that DNA hairpins template the site-specificassembly offluorescent few-atom Ag clusters on DNA nanotubes. Fluorescent clustersform only at hairpin sites and not on the double-stranded DNA scaffold,allowing for spatially programmed self-assembly. Ag clusters synthesizedon hairpins protruding from DNA nanotubes can have nearly identicalfluorescence spectra to those synthesized on free hairpins of identicalsequence. Analysis of the stepwise photobleaching of individual clusterssuggests a chemical yield of ∼45%. Given the well-establishedsequence-specific optical properties of DNA stabilized Ag clusters,these results point the way toward high yield assembly of metal clusterfluorophores with control over spectra as well as spatial arrangement. [ABSTRACT FROM AUTHOR]

A cluster obtained in high yield from the reduction ofa silver-thiolateprecursor, Ag-SCH2CH2Ph, exhibited a singlesharp peak near 25 kDa in the matrix-assisted laser desorption massspectrum (MALDI MS) and a well-defined metal core of ∼2 nmmeasured with transmission electron microscopy (TEM). The clusteryields a single fraction in high-performance liquid chromatography(HPLC). Increased laser fluence fragments the cluster until a newpeak near 19 kDa predominates, suggesting that the parent clusterAg152(SCH2CH2Ph)60evolvesinto a stable inorganic coreAg152S60. Exploiting combined insights from investigations of clusters andsurface science, a core–shell structure model was developed,with a 92-atom silver core having icosahedral-dodecahedral symmetryand an encapsulating protective shell containing 60 Ag atoms and 60thiolates arranged in a network of six-membered rings resembling thegeometry found in self-assembled monolayers on Ag(111). The structureisin agreement with small-angle X-ray scattering (SAXS) data. The protectivelayer encapsulating this silver cluster may be the smallest knownthree-dimensional self-assembled monolayer. First-principles electronicstructure calculations show, for the geometry-optimized structure,the development of a ∼0.4 eV energy gap between the highest-occupiedand lowest-unoccupied states, originating from a superatom 90-electronshell-closure and conferring stability to the cluster. The opticalabsorption spectrum of the cluster resembles that of plasmonic silvernanoparticles with a broad single feature peaking at 460 nm, but theluminescence spectrum shows two maxima with one attributed to theligated shell and the other to the core. [ABSTRACT FROM AUTHOR]

A novel strategy was designed to prepare Ag cluster-dopedTiO2nanoparticles (Ag/TiO2NPs) without additionofany chemical reducing agent and/or organic additive. A defect-richTiOxspecies was generated by laser ablationin liquid (LAL) of a Ti target. The silver ions could be reduced anddeposited on the surface of TiO2NPs through the removalof oxygen vacancies and defects; the TiOxspecies evolved into anatase NPs in a hydrothermal treatment process.The derived Ag/TiO2NPs are approximately 25 nm in size,with narrow size distribution. The Ag clusters are highly dispersedinside TiO2and less than 3 nm in size. The doped amountcan be tuned by changing the concentration of Ag+ions.The as-synthesized Ag/TiO2NPs display improved photocatalyticefficiency toward pentachlorophenol (PCP) degradation. [ABSTRACT FROM AUTHOR]

The aggregation behaviors of silver atoms modulated bypolymorphicDNA templates involving i-motif, G-quadruplex, and the Watson–Crickduplex, were investigated by using the density functional theory (DFT)calculations, combining with the experimental characterizations ofCD, UV, fluorescence measurements and TEM, in order to understandthe reason in the molecular level that polymorphic DNA templates affectthe fluorescence emitting species of Ag nanomaterials. First, theaffinity sites of silver ions on different DNA templates were analyzedby using DFT calculations, and the conformational variations of DNAtemplates caused by silver ions and atoms were disclosed. Second,the aggregation behaviors of silver atoms constrained by the polymorphicDNA templates were studied by DFT modeling, and distinct fluorescenceproperty of nanosilvers templated by polymorphic DNA were evaluatedusing the time-dependent DFT calculations. It is illustrated thatwith the DNA template adopting i-motif or the duplex the silver atomstend to aggregate inside the encapsulated spaces of nucleobases, andthe formed silver nanoclusters are positively charged with high fluorescentspectral features; whereas with the template of the G-quadruplex thesilver atoms are preferential to aggregate outside of the G-tetrad,which results in the formation of larger silver crystals without fluorescenceproperty. The results obtained here are useful to explore the nucleationand growth mechanism of silver nanomaterials regulated by the structure-specificDNA templates, which is important to rational design of desirablefluorescent emitters for sensing in the field from biology to nanoscience. [ABSTRACT FROM AUTHOR]

Few-atom silver clusters harbored by DNA are promising fluorophores due to their high molecular brightness along with their long- and short-term photostability. Furthermore, their emission rate can be enhanced when co-illuminated with low-energy light that optically depopulates the fluorescence-limiting dark state. The photophysical basis for this effect is evaluated for two near-infrared-emitting clusters. Clusters emitting at ∼800 nm form with C3AC3AC3TC3A and C3AC3AC3GC3A, and both exhibit a trap state with λmax∼ 840 nm and an absorption cross section of (5–6) × 10–16cm2/molecule that can be optically depopulated. Transient absorption spectra, complemented by fluorescence correlation spectroscopy studies, show that the dark state has an inherent lifetime of 3–4 μs and that absorption from this state is accompanied by photoinduced crossover back to the emissive manifold of states with an action cross section of ∼2 × 10–18cm2/molecule. Relative to C3AC3AC3TC3A, C3AC3AC3GC3A produces a longer-lived trap state and permits more facile passage back to the emissive manifold. With the C3AC3AC3AC3G template, a spectrally distinct cluster forms having emission at ∼900 nm, and its trap state has a ∼4-fold shorter lifetime. These studies of optically gated fluorescence bolster the critical role of the nucleobases in both the formation and excited state dynamics of these highly emissive metallic clusters. [ABSTRACT FROM AUTHOR]

We employ ab initio calculations of van der Waals complexes to study the potential energy parameters (C6coefficients) of van der Waals interactions for modeling of the adsorption of silver clusters on the graphite surface. Electronic structure calculations of the (Ag2)2, Ag2−H2, and Ag2−C6H6complexes are performed using a coupled-cluster approach that includes single, double, and perturbative triple excitations (CCSD(T)), Møller−Plesset second-order perturbation theory (MP2), and spin-component-scaled MP2 (SCS-MP2) methods. Using the atom pair approximation, the C6coefficients for silver−silver, silver−hydrogen, and silver−carbon atom systems are obtained after subtracting the energies of quadrupole−quadrupole interactions from the total electronic energy. [ABSTRACT FROM AUTHOR]

The structures of silver clusters from Ag121to Ag160were optimized with a modified dynamic lattice searching (DLS) method, named as DLS with constructed core (DLSc). The interaction among silver atoms is modeled by the Gupta potential. Structural characteristic of silver clusters with the growth of cluster size is investigated with the newly optimized structures and our previous results from Ag13to Ag120. A set of amorphous structures was obtained in the size range of 13−48, together with several ordered structures. The putative stable motif is an icosahedron from Ag49to Ag61and then changes to a decahedron in the size range of 62−160. Some of the results are consistent with experiments. Furthermore, it was also found that, for clusters with decahedral motif, the stable structure is a result of the competition among the different Marks decahedral motifs. On the other hand, different from the Lennard-Jones cluster, there are some silver clusters with the face-centered cubic (fcc) motif in the size range of 13−160. But the fcc motif can only be obtained for some specific sizes. [ABSTRACT FROM AUTHOR]

We report the synthesis and chiroptical properties of silver nanocluster enantiomers. The surface of the silver nanoclusters is covered with l/d-penicillamine or their racemate. The clusters are separated by gel electrophoresis according to their charge and size into well-defined compounds. The mean core diameter of each fractioned component varies from 1 to 3 nm. The separated compounds of silver nanoclusters covered with l- or d-form thiol show strong optical activity or circular dichroism with opposite sign (mirror image relationship) in the metal-based electronic transitions (obtained anisotropy factor is on the order of 1 × 10-3to 1 × 10-5), suggesting that the nanoclusters have well-defined stereostructures as common chiral molecules do. With a decrease in the mean cluster diameter, the anisotropy factor gradually increases at first, but a steep rise is observed when the diameter becomes smaller than ∼1.5 nm. The chiroptical response of the silver nanoclusters is consequently several-fold larger than that of the gold nanoclusters having the same ligand. The possibilities of a dissymmetric field model as well as an inherently chiral core model are discussed as the origin of the intense optical activity. [ABSTRACT FROM AUTHOR]

CO adsorption on small neutral, anionic, and cationic silver clusters Agn (n = 1−7) has been studied with use of the PW91PW91 density functional theory (DFT) method. The adsorption of CO on-top site, among various possible sites, is energetically preferred irrespective of the charge state of the silver cluster. The cationic silver clusters generally have a greater tendency to adsorb CO than the anionic and neutral silver ones, except for n = 3 and 4, and the binding energies reach a local minimum at n = 5. The binding energies on the neutral clusters, instead, reach a local maximum at n = 3, which is about 0.87 eV, probably large enough to be captured in the experiments. Binding of CO to the silver clusters is generally weaker than that to the copper and gold counterparts at the same size and charge state. This is due to the weaker orbital interaction between silver and CO, which is caused by the larger atomic radius of the silver atom. In contrast, Au atoms with a larger nuclear charge but a similar atomic radius to silver owing to the lanthanide contraction are able to have a stronger interaction with CO. [ABSTRACT FROM AUTHOR]

Three silver(I) cluster-based coordination polymers, namely, [Ag3(podc)(H2O)2]·2H2O (1), [Ag2(pidc)] (2), and [Ag2(pidc)(H2O)] (3) (H3podc = 3,5-pyrazoledicarboylic acid and H2pidc = 2,3-pyrazinedicarboxylic acid) have been synthesized. Among them, 1 consists of stairlike one-dimensional chains with boxlike units as well as the zigzag tetranuclear silver(I) cluster subunits [Ag···Ag 2.778(1) and 3.230(1) Å]; 2 features new parallel single-strand silver(I) helices that propagate by the 41-screw symmetry with short Ag···Ag contacts [Ag2···Ag2 3.158(1) Å] along the c-axis and display the same handedness, while 3 features hexagonal Ag4(μ2-O)2 cores, in which the Ag···Ag separation is 3.150(2) Å. These complexes display room temperature photoluminescence in the blue/green region, which may be assigned to an admixture of ligand-to-metal charge transfer and metal-centered (d-s/d-p) transitions. [ABSTRACT FROM AUTHOR]

Ag cluster formation on AgBr is probed in three ways. First, qualitative orbital arguments, largely based on symmetry considerations, are introduced to determine which AgBr surfaces are more likely to lead to silver cluster formation induced by photoelectrons. The analysis indicates that silver atoms on the (111) surface and the troughs and wedges of a twin plane are likely to form clusters. Silver atoms on (100) and (110) surfaces do not appear to possess the electronic features favoring cluster formation. Second, DFT electronic structure calculations performed on cluster models produced trends similar to those emerging from the group theoretical analysis. Third, we looked at electron density shifts in models specifically constructed to create contrasting bonding environments on AgBr surfaces. An increase in electron density on the essential silver atoms is observed in a triplet state model for photoinduced cluster formation. [ABSTRACT FROM AUTHOR]

Singly positively and negatively charged silver-cluster ions were effectively produced under matrix-assisted laser desorption/ionization (MALDI) conditions up to the aggregation number of n ≅ 200, using reductive polar organic matrixes and silver trifluoroacetate (AgTFA). It was found that the matrix greatly influences the resulting cluster ion abundances. The effect of the matrixes with various chemical structures on the cluster formation was systematically investigated. It was also observed that the ion intensities decreased sharply at particular cluster numbers called “magic” numbers, independently of the matrix used, and this is in good agreement with the jellium model theory. The highest observed magic numbers were achieved with HABA [2-(4-hydroxyphenylazo)benzoic acid] and are 139 and 137 for positively and negatively charged cluster ions, respectively. The fragmentations of both singly positively and negatively charged clusters ions were also studied. It was found that even-number clusters lose one silver atom, while clusters with an odd-number emit a single or two silver atoms. The fragmentation behavior of clusters as a function of the cluster size is reported. On the basis of the results a possible mechanism for the cluster ion formation is also presented. [ABSTRACT FROM AUTHOR]

Magic-number theories, developed to explain the anomalous stability of clustes in the gas phase, are being successfully applied to explain the stability of families of condensed phase Au clusters. To test the generalizability of these theories, we have synthesized a family of magic-numbered Ag clusters. Silver clusters ligated with glutathione (GSH) were synthesized by reduction of silver glutathiolate in water and then separated by polyacrylamide gel electrophoresis (PAGE). The raw synthetic product consisted of a family of discrete Ag:SG clusters, each forming a band in the PAGE gel. Varying reaction conditions changed the relative abundance of the family members but not their positions and colors within the gel, indicating the molecular precision of magic-number clusters. Absorption onsets for the most abundant clusters monotonically decreased with increasing cluster size, and spectra contained a small number of peaks that corresponded to single electron transitions. Although these Ag: SG clusters are related to Au:SG clusters, the distribution of cluster sizes and the optical absorption spectra were markedly different for the two families. This suggests that the Ag:SG clusters are not a simple extension of the Au:SG system, possibly due to differences in Au and Ag chemistry. Alternatively, condensed-phase magic-number cluster theories may need to be more complex than currently believed. [ABSTRACT FROM AUTHOR]