Formation of binary silver sulfide clusters and sulfur sensitization of photographic process

Formation of silver sulfide binary cluster ions,as well as the effects of silver and sulfur content proportion,the cluster size range,the influence of laser fluence,the UV laser photolysis,etc.,was studied with the laser ablation method and a tandem time-of-flight mass spectrometer.The results show that there exist two different forms of positively charge-bearing cluster ions;[(Ag2S)n Ag] + and [ (Ag2S)n-1 Ag3]+.The most possible forms of the sulfur sensitization centers acting as traps of photoelectrons are [Ag2S] +,[ Ag2S Ag] +,[ Ag2S Ag3]+ and the analogs.     

Molecular simulation of interactions between silver clusters and an α-quartz surface

The adsorption of silver clusters Ag _n (n = 1–7) on different sites of an α-SiO₂ (0001) surface is studied using density functional theory calculations in the general gradient approximation. The most stable configurations of Ag _n (n = 1–7) adsorbed on the α-SiO₂ surface are determined, and the correlations between cluster size and adsorption energy are found. It is established that the optimized geometry parameters of Ag _n (n = 1–7) and the values of their adsorption energy are in good agreement with the results from earlier investigations and confirm the validity of the chosen theoretical model.     

Theoretical study of “sandwich” clusters of fused magnesium porphyrin oligomers with alkali metal atoms

The structural characteristics, energies, and spectroscopic properties of two-layer and multilayer “sandwich” clusters in which rings (layers) of fused porphyrin oligomers Mg₂P₂ and Mg₄P₄ (P = C₂₀H₁₂N₄) are separated by (Li) _n metal interlayers containing from 8 to 32 lithium atoms have been calculated by the density functional theory B3LYP method. The trends in the changes in these characteristics have been scrutinized as a function of the number of introduced Li atoms and the size and number of porphyrin layers. Calculations predict the high energetic stability and possibility of the existence of these sandwiches as paramagnetic clusters with mobile intercalated lithium ions. The latter, like intercalated graphite clusters, are expected to exhibit high electronic and ionic conductivity. The most favorable (with low or zero barriers) channels of migration of metal ions between the porphyrin layers are discussed.     

Octahedral and tetrahedral coinage metal clusters: is three-dimensional d-orbital aromaticity viable?

The first quantitative evidence for the viability of three-dimensional aromatic clusters involving d-orbitals in pseudo-octahedral coinage metal cages M(6)Li(2) (M = Cu, Ag, Au) as well as in tetrahedral coinage metal cages M'(4)Li(4) (M' = Cu, Ag) was obtained computationally. These cages exhibit many features similar to those of their square planar M(4)Li(2) analogues. The large negative nucleus-independent chemical shifts (NICS) at the cage centers indicate three-dimensional delocalization. This diatropic character arises mostly from d-orbital delocalization combined with substantial contributions from the lowest-valence orbitals. The bonding molecular orbitals of the pseudo-octahedral clusters M(6)Li(2) (M = Cu, Ag, Au) are analogous to those in similar octahedral clusters involving p-orbital delocalization (e.g., B(6)H(6)(2-)). The M'(4)Li(4) clusters exhibit two isomeric forms: metal tetrahedral cages tetracapped by lithium cations on the outside [(M'(4)).4Li] and lithium tetrahedra on the inside capped by coinage metal atoms on each of the four faces [(Li(4)).4M]. Whereas the (M'(4)).4Li type structure is preferred for copper, gold and silver favor the (Li(4)).4M arrangement. NBO-NICS analysis shows that the large diatropic character in (M'(4)).4Li structures is due to the favorable contribution from both s- and d-orbitals, whereas the small NICS values in the center of (Li(4)).4M are due only to the diatropic contributions from the s-orbitals.     

Synthesis,structure and isomerism of “three-bridge” exo-nido-osmacarborane clusters

The reaction of OsCl₂(PPh₃)₃ with [nido-7-R¹-8-R²-C₂B₉H₁₀]K⁺ produced a series of new exo-nido-osmacarborane complexes exo-nido-5,6,10-[Cl(Ph₃P)₂Os]-5,6,10-(-H)₃-10-H-7-R¹-8-R²-7,8-C₂B₉H₆ (1: R¹ = R² = H; 2: R¹ = R² = Me; 3: R¹ = R² = PhCH₂; 4: R¹ + R² = 1,2-C₆H₄(CH₂)₂; 5: R¹ = H, R² = Me) in which the osmium-containing group is linked to the nido-carborane ligand through three two-electron three-center bonds. Compounds 1—5 are formed as mixtures of symmetric (a) and asymmetric (b) isomers; pure symmetric isomers 2a and 4a were isolated by fractional crystallization, and the mixture of isomers 3a, was quantitatively separated into individual compounds 3a and 3b by column chromatography on silica gel. Detailed analysis of the ³¹P{¹H}, ¹H, ¹¹B NMR spectra of 1a,b—5a,b and 2D ¹H-¹H{¹¹B} and ¹¹B{¹H}-¹¹B{¹H} NMR spectra of 3a and 3b was performed. The structures of isomers 2a and 4a were confirmed by an X-ray diffraction study. According to the NMR and X-ray diffraction data, the isomerism of exo-nido-complexes 1a,b—5a,b is actually the cis—trans-isomerism of ligand arrangement in the octahedral coordination of the Os atom.     

Defect of nanocrystalline copper and silver

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Surface-enhanced Raman spectroscopic study of the metal—sulfur bonding: Adsorption of N,N-dimethyl-thioformamide on copper and silver electrodes

Surface-enhanced Raman spectroscopy has been used to study the adsorption of N,N-dimethyl-thioformamide (DMTF) on Cu and Ag electrodes. Similar to the cases of thiourea and thioacetamide, the predominantly CS stretching band at 975 cm⁻¹ of DMTF is shifted to lower frequencies by about 30–40 cm⁻¹ upon adsorption on Cu and Ag surfaces. We conclude that DMTF is S-bonded to the metal surfaces. The frequency shifts of the CS stretch resemble those observed for the organometallic complexes of DMTF.     

Electrochemical deposition of copper in polyaniline films — number density and spatial distribution of deposited metal clusters

The electrochemical deposition of copper in reduced polyaniline (PAN) films is studied at different polymer layer thicknesses. A saturation in the number density, n₀, of active sites for metal deposition is found at 0.5 μm PAN thickness (n₀=10⁸ cm⁻²). The surface spatial distribution of the deposited copper crystals is analysed in two cases. It is found that nucleation exclusion zones play an appreciable role in the course of the deposition process in thin PAN films. In contrast, a random distribution and a larger number of deposited crystals are obtained in thicker PAN layers.     

Can an electron-shell closing model explain the structure and stability of ligand-stabilized metal clusters?

We investigated the structure and stability of several aluminum hydride complexes to understand the essence of "superatom chemistry" and to gain a right perspective on the ligand (L)-stabilized metal (M) clusters. We successfully interpret the structure and stability using molecular orbital analysis, which clearly shows the failure of an electron-shell closing model (or a superatom model) to explain it. The structure and stability of Al(m)H(n) are closely associated with the molecular orbital stabilization owing to the effective orbital overlap between Al(m) (M(m)) and nH (nL). The importance of retaining the electronic structural integrity of M(m) in M(m)L(n)-within an electron-shell closing model-has been underestimated or even disregarded, and this has created the current controversies in the scientific community.     

Review: Multimetallic silver(I)–pyridinyl complexes: coordination of silver(I) and luminescence

This review highlights some structural features and luminescent properties of homo- and hetero-multinuclear silver(I)–pyridinyl complexes. It focuses on the coordination and geometry of the silver(I) ions to the pyridinyl-nitrogen. For this reason, we have considered only pyridinyl-N–Ag(I) complexes whose crystal data are available. In addition, this review does not consider mononuclear silver(I)–pyridinyl complexes as these have been reviewed elsewhere. This is motivated by the fact that multinuclear silver(I)–pyridinyl complexes have been shown to be more stable in solution, possess enhanced properties, and have fascinating structures compared to their mononuclear counterparts. The introduction highlights pyridinyl ligands used in complexation of silver(I) ions. The main body highlights complexation of silver(I) through pyridinyl nitrogen and the interactions found in the multinuclear silver(I)–pyridinyl complexes as well as the coordination number and geometry of silver(I) centers. Though silver(I) has been flaunted to prefer linear twofold coordination geometry, from this review, it is clear that higher coordination numbers in varied geometries are possible. These include distorted trigonal planar, T-shaped, distorted tetrahedral, trigonal bipyramidal, and octahedral geometries. Coordination of silver(I) to pyridinyl ligands and their metalloligands has been observed to impart or enhance luminescent properties in the ensuing complexes.     

Photoionization studies of transition metal clusters: Ionization potentials of ScnO (n=5−36)

The photoionization efficiency (PIE) spectra and ionization potentials are reported for scandium cluster monoxides (Sc _n O,n=5–36). As found for other transition metal clusters, strong dependence of ionization potential on cluster size is found for small clusters, with the ionization potentials of larger clusters decreasing relatively smoothly with increasing size. The IPs are 0.6–0.8 eV lower than that predicted by conducting spherical droplet model.Performed at Argonne National Laboratory     

Topography of scalar fields: molecular clusters and π-conjugated systems

The pioneering works due to Bader and co-workers have generated widespread interest in the study of the topography of molecular scalar fields, the first step of which is the identification and characterization of the corresponding critical points (CPs). The topography of a molecular system becomes successively richer in going from the bare nuclear potential (BNP) to the molecular electrostatic potential (MESP) through the molecular electron density (MED). The present work clearly demonstrates, through the study of some π-conjugated test molecules as well as molecular clusters, that the CPs could be economically located by following this path within ab initio level theory. Further, the topography mapping of large molecules, especially at a higher level of theory, is known to be a demanding task. However, it is rendered possible by following the above sequential mapping assisted by a divide-and-conquer-type method termed as the molecular tailoring approach (MTA). This is demonstrated with the topography mapping of β-carotene and benzene nonamer at MP2 and a (H(2)O)(32) cluster at the HF level of theory, which are rather challenging problems with contemporary off-the-shelf computer hardware.     

How many metal atoms are needed to dehydrogenate an ethylene molecule on metal clusters?: Correlation between reactivity and electronic structures of Fen+, Con+, and Nin+

The absolute cross section for dehydrogenation of an ethylene molecule on Mn+ [Fen+ (n = 2-28), Con+ (n = 8-29), and Nin+ (n = 3-30)] was measured as a function of the cluster size n in a gas-beam geometry at a collision energy of 0.4 eV in the center-of-mass frame in an apparatus equipped with a tandem-type mass spectrometer. It is found that (1) the dehydrogenation cross section increases rapidly above a cluster size of approximately 18 on Fen+, approximately 13 and approximately 18 on Con+, and approximately 10 on Nin+ and (2) the rapid increase of the cross section for Mn+ occurs at a cluster size where the 3d electrons start to contribute to the highest occupied levels of Mn+. These findings lead us to conclude that the 3d electrons of Mn+ play a central role in the dehydrogenation on Mn+.     

“Aggregation-induced emission” of transition metal compounds: Design,mechanistic insights,and applications

In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.Since the discovery of AIE, many AIE-active materials have been developed, most of them composed of organic molecules, and thus fluorescent in nature. Although a wide range of applications such as bioimaging, sensing, multi-stimuli responsive materials, and optoelectronic devices have been proposed for this new class of materials, triplet harvesting phosphorescent materials have much longer lifetimes as compared to their singlet harvesting analogues, and for this particular reason, the development of AIE-active phosphorescent materials seems to be a promising strategy from the applications point of view. In this respect, the synthesis of new AIE-active systems including heavy metals that would facilitate the population of low-lying excited triplet states via spin-orbit coupling (SOC), for which the strength increases as the fourth power of atomic number, i.e. Z⁴, is highly desirable. This review covers the design and synthetic strategies used to obtain the AIEgens reported in the literature that contain either d-block metals such as Cu(I), Zn(II), Re(I), Ru(II), Pd(II), Ir(III), Pt(II), Au(I), and Os(IV), describing the mechanisms proposed to explain their AIE. New emerging high-tech applications such as OLEDs, chemical sensors or bioimaging probes proposed for these materials are also discussed in a separate section.     

Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

Molecular and electronic structures, Brönsted basicities, and Lewis acidities of group VIB transition metal oxide clusters

The structures and properties of transition metal oxide (TMO) clusters of the group VIB metals, (MO(3))(n) (M = Cr, Mo, W; n = 1-6), have been studied with density functional theory (DFT) methods. Geometry optimizations and frequency calculations were carried out at the local and nonlocal DFT levels with polarized valence double-zeta quality basis sets, and final energies were calculated at nonlocal DFT levels with polarized valence triple-zeta quality basis sets at the local and nonlocal DFT geometries. Effective core potentials were used to treat the transition metal atoms. Two types of clusters were investigated, the ring and the chain, with the ring being lower in energy. Large ring structures (n > 3) were shown to be fluxional in their out of plane deformations. Long chain structures (n > 3) of (CrO(3))(n) were predicted to be weakly bound complexes of the smaller clusters at the nonlocal DFT levels. For M(6)O(18), two additional isomers were also studied, the cage and the inverted cage. The relative stability of the different conformations of M(6)O(18) depends on the transition metal as well as the level of theory. Normalized and differential clustering energies of the ring structures were calculated and were shown to vary with respect to the cluster size. Br?nsted basicities and Lewis acidities based on a fluoride affinity scale were also calculated. The Br?nsted basicities as well as the Lewis acidities depend on the size of the cluster and the site to which the proton or the fluoride anion binds. These clusters are fairly weak Br?nsted bases with gas phase basicities comparable to those of H(2)O and NH(3). The clusters are, however, very strong Lewis acids and many of them are stronger than strong Lewis acids such as SbF(5). Br?nsted acidities of M(6)O(19)H(2) and M(6)O(18)FH were calculated for M = Mo and W and these compounds were shown to be very strong acids in the gas phase. The acid/base properties of these TMO clusters are expected to play important roles in their catalytic activities.     

Synthesis,structures and electrochemical properties of four organic–inorganic hybrid polyoxometalates constructed from polyoxotungstate clusters and transition metal complexes

Four novel organic–inorganic hybrid compounds [Cu₅ ^I(4,4′-bpy)₃(2,2′-bpy)₄][BW₁₂O₄₀] · H₂O (1), [Ni_0.5(2,2′-bpy)_1.25][Ni(2,2′-bpy)₃][Ni(2,2′-bpy)₂(H₂O)(SiW₁₁^VIW^VO₄₀)] · 0.5H₂O (2), [H₂bpy]₂[Zn(2,2′-bpy)₃]₂[Si₂W₁₈O₆₂] · 1.5H₂O (3) and [Cu^II(2,2′-bpy)₂]₂[SiW₁₂O₄₀] · 2H₂O (4) (2,2′-bpy = 2,2′-bipyridine, 4,4′-bpy = 4,4′-bipyridine) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal gravimetric analysis, electrochemical measurements and single-crystal X-ray diffraction. Compound (1) is a novel [BW₁₂O₄₀]⁵⁻ polyoxoanion bisupported by copper(I) coordination cations with mixed 2,2′-bpy and 4,4′-bpy ligands. Compound (2) is constructed from the [SiW₁₁^VIW^VO₄₀]⁵⁻ polyoxoanions supported by [Ni(2,2′–bpy)₂]²⁺. Compound (3) is composed of a novel [Si₂W₁₈O₆₂]⁸⁻ cluster and [Zn(2,2′–bpy)₃]²⁺ complexes, which held together into a three-dimensional (3D) supramolecular network through hydrogen-bonding interactions. Compound (4) shows a 2D layer framework constructed from a bisupporting Keggin polyoxoanion cluster and [Cu(2,2′–bpy)₂]²⁺ coordination polymer fragments, resulting in 3D networks via supramolecular interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.