共查询到20条相似文献,搜索用时 15 毫秒
1.
Raquel Utrera‐Melero Jean‐Yves Mevellec Nicolas Gautier Nicolas Stephant Florian Massuyeau Sandrine Perruchas 《化学:亚洲杂志》2019,14(18):3166-3172
The aggregation‐induced emission (AIE) properties of two different copper iodide clusters have been studied. These two [Cu4I4L4] clusters differ by their coordinated phosphine ligand and the luminescent mechanochromic properties are only displayed by one of them. The two clusters are AIE‐active luminophors that exhibit an intense emission in the visible region upon aggregation. The formed particles present luminescent thermochromism comparable to that of the bulk compounds. The observed AIE properties can be attributed to suppression of nonradiative relaxation of the excited states in a more rigid state, in relation to the large structural relaxation of the excited triplet state. The differences observed in the AIE properties of the two clusters can be related to the different ligands. A correlation between the luminescence mechanochromic properties and the AIE effect is not straightforward, but the formation of “soft” molecular solids is a common characteristic that can explain the photoactive properties of these compounds. 相似文献
2.
Monitoring coalescence behavior of soft colloidal particles in water by small-angle light scattering
Dan Wei Hua Wu Zhengbin Xia Delong Xie Li Zhong Massimo Morbidelli 《Colloid and polymer science》2012,290(11):1033-1040
The fractal dimension (D f) of the clusters formed during the aggregation of colloidal systems reflects correctly the coalescence extent among the particles (Gauer et al., Macromolecules 42:9103, 2009). In this work, we propose to use the fast small-angle light scattering (SALS) technique to determine the D f value during the aggregation. It is found that in the diffusion-limited aggregation regime, the D f value can be correctly determined from both the power law regime of the average structure factor of the clusters and the scaling of the zero angle intensity versus the average radius of gyration. The obtained D f value is equal to that estimated from the technique proposed in the above work, based on dynamic light scattering (DLS). In the reaction-limited aggregation (RLCA) regime, due to contamination of small clusters and primary particles, the power law regime of the average structure factor cannot be properly defined for the D f estimation. However, the scaling of the zero angle intensity versus the average radius of gyration is still well defined, thus allowing one to estimate the D f value, i.e., the coalescence extent. Therefore, when the DLS-based technique cannot be applied in the RLCA regime, one can apply the SALS technique to monitor the coalescence extent. Applicability and reliability of the technique have been assessed by applying it to an acrylate copolymer colloid. 相似文献
3.
The Origin of the Selectivity and Activity of Ruthenium‐Cluster Catalysts for Fuel‐Cell Feed‐Gas Purification: A Gas‐Phase Approach
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Dr. Sandra M. Lang Prof. Dr. Thorsten M. Bernhardt Marjan Krstić Prof. Dr. Vlasta Bonačić‐Koutecký 《Angewandte Chemie (International ed. in English)》2014,53(21):5467-5471
Gas‐phase ruthenium clusters Run+ (n=2–6) are employed as model systems to discover the origin of the outstanding performance of supported sub‐nanometer ruthenium particles in the catalytic CO methanation reaction with relevance to the hydrogen feed‐gas purification for advanced fuel‐cell applications. Using ion‐trap mass spectrometry in conjunction with first‐principles density functional theory calculations three fundamental properties of these clusters are identified which determine the selectivity and catalytic activity: high reactivity toward CO in contrast to inertness in the reaction with CO2; promotion of cooperatively enhanced H2 coadsorption and dissociation on pre‐formed ruthenium carbonyl clusters, that is, no CO poisoning occurs; and the presence of Ru‐atom sites with a low number of metal–metal bonds, which are particularly active for H2 coadsorption and activation. Furthermore, comprehensive theoretical investigations provide mechanistic insight into the CO methanation reaction and discover a reaction route involving the formation of a formyl‐type intermediate. 相似文献
4.
《印度化学会志》2022,99(11):100753
Density Functional Theory (DFT) computations were performed to investigate the optical properties of dihydropyrimidine (DHP) and metal clusters of copper (Cu), gold (Au), and silver (Ag). The charge transfers from the metal cluster to DHP through the NH group are revealed by molecular electrostatic potential (MEP) surface and Mulliken charge analysis. Bonding and antibonding orbitals of the DHP-adsorbed metal clusters are responsible for the surface resonance peak in the UV–Vis spectra of DHP adsorbed metal clusters. The polarizability values of DHP-adsorbed on metal clusters are very high in comparison with that of pristine DHP, which suggests an increase in the Non-linear optical (NLO) effect. Our study explores that the DHP adsorbed metal clusters could be used for the NLO materials. The vibrational modes of DHP are enhanced in the DHP adsorbed metal clusters due to surface-enhanced Raman scattering (SERS). Solvation energy is found to be ?21.01, ?29.37, and ?27.82 kcal/mol for DHP-Ag3/Au3/Cu3 which means the DHP-adsorbed metal clusters are stable in thr aqueous medium. The atom in molecule-reduced density gradient (AIM-RDG) isosurface shows weak non-covalent interactions in each DHP adsorbed metal clusters. 相似文献
5.
V. Bonačić-Koutecký J. Pittner R. Pou-Amérigo M. Hartmann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):445-447
Structural and optical properties of nonstoichiometric LinO and NanO (n = 3, 4) clusters containing one and two excess electrons are studied using ab-initio methods accounting for electron correlation. We show that calculated absorption patterns are excellent fingerprints of structural and bonding properties. The optical response of Li4O and Na4O clusters with the most stable tetrahedral type structures is characterized by a common feature, that is the appearance of a dominant intense transition in infrared regime although excess of electrons are not localized, as it is the case for small alkali-halide clusters, with cuboid corner vacancy (surface F-center in finite systems). 相似文献
6.
Dr. Uttam Chakraborty Efrain Reyes‐Rodriguez Dr. Serhiy Demeshko Prof. Dr. Franc Meyer Prof. Dr. Axel Jacobi von Wangelin 《Angewandte Chemie (International ed. in English)》2018,57(18):4970-4975
While the coordination chemistry of monometallic complexes and the surface characteristics of larger metal particles are well understood, preparations of molecular metallic nanoclusters remain a great challenge. Discrete planar metal clusters constitute nanoscale snapshots of cluster growth but are especially rare owing to the strong preference for three‐dimensional structures and rapid aggregation or decomposition. A simple ligand‐exchange procedure has led to the formation of a novel heteroleptic Mn6 nanocluster that crystallized in an unprecedented flat‐chair topology and exhibited unique magnetic and catalytic properties. Magnetic susceptibility studies documented strong electronic communication between the manganese ions. Reductive activation of the molecular Mn6 cluster enabled catalytic hydrogenations of alkenes, alkynes, and imines. 相似文献
7.
The optical response of alkali metal clusters is shown to be sensitive to a proper treatment of the electronion interaction and to the ionic spatial structure. A spherical symmetry model based on a combination of a geometrical optimization of the ionic structure and the random phase approximation (RPA) with exact exchange is applied to calculate the optical response of Li
139
+
. The optical response obtained within this model is in good agreement with the measured giant dipole resonance. 相似文献
8.
A. V. Butenko P. A. Chubakov Yu. E. Danilova S. V. Karpov A. K. Popov S. G. Rautian V. P. Safonov V. V. Slabko V. M. Shalaev M. I. Stockman 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,17(4):283-289
Linear and nonlinear optical properties of metal fractal clusters are studied. Experimental evidence is presented proving that clusters possess unique optical nonlinearities, characterized by rapid response, broadbandness and enormously high values of nonlinear susceptibility. A 106 times enhancement of the DFWM signal has been observed experimentally in silver particles aggregated into clusters. For the first time frequency-and polarization-selective photomodification of fractal silver clusters has been realized. 相似文献
9.
The optical response of colloidal particles depends on a variety of properties of the cluster, e.g., shape, size, size distribution and particle material. Since particles often are charged, also the surface charge may be a parameter which influences their optical properties. In this paper the effect of a surface charge on optical properties of spherical colloidal particles is studied and its magnitude is estimated by extended computations for silver clusters with surface plasmon in aqueous suspension. Two models are presented and discussed. The first model is based on the electrodynamic solution by Bohren and Hunt (Can. J. Phys. 55, 1930 (1977)), where a surface conductivity S for a free surface charge yield an additional contribution S to the dielectric constant of the particle material. In the second model, the surface charge contributes to the number density of free electrons in the cluster. Both models lead to a shift of the cluster plasmon peak, while an increase of the plasmon halfwidth could not be derived. The effect is quite small and limited on very small clusters.PACS 61.46+w 73.20.Mf 78.20.Dj 相似文献
10.
Atomically Precise Multimetallic Semiconductive Nanoclusters with Optical Limiting Effects
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Shuai Chen Dr. Wei‐Hui Fang Prof. Dr. Lei Zhang Prof. Dr. Jian Zhang 《Angewandte Chemie (International ed. in English)》2018,57(35):11252-11256
For the first time, multinuclear noble‐metal clusters have been successfully stabilized by Ti‐oxo clusters. Two unprecedented Ag6@Ti16‐oxo nanoclusters with precise atomic structures were prepared and characterized. The octahedral Ag6 core has strong Ag?Ag bonds (ca. 2.7 Å), and is further stabilized by direct Ag?O?Ti coordination interactions. Moreover, as a result of different acidic/redox conditions in synthesis, the Ag6 core can adopt diverse geometric configurations inside the Ti16‐O shell. Correspondingly, structural differences greatly influence their optical limiting effects. The transmittance reduction activity of the clusters towards 532 nm laser shows a nearly linear concentration dependence, and can be optimized up to about 43 %. This work not only opens a new direction for multimetallic semiconductive nanoclusters with interesting optical properties, but also provides molecular models for important noble‐metal/TiO2 heterogeneous materials. 相似文献
11.
We have used molecular simulations to study the properties of nanocomposites formed by the chemical incorporation of polyhedral
oligomeric silsesquioxane (POSS) particles in the cross-linked epoxy network. The particular POSS molecule chosen—glycidyloxypropyl-heptaphenyl
POSS—can form only one bond with the cross-linker and thus was present as a dangling unit in the network. Four epoxy-POSS
nanocomposites containing different fractions (up to 30 mass/%) of POSS particles were studied in this work. Well-relaxed
atomistic model structures of the nanocomposites were created and then molecular dynamics simulations were used to characterize
the density, glass transition temperature (T
g), and the coefficient of volume thermal expansion (CVTE) of the systems. In addition to the effect of nanoparticle loading,
the effect of nanoparticle chemistry on the nanocomposite properties was also characterized by comparing these results with
our previous results (Lin and Khare, Macromolecules 42:4319–4327, 2009) on neat cross-linked epoxy and a nanocomposite containing
a POSS nanoparticle that formed eight bonds with the cross-linked network. Our results showed that incorporation of these
monofunctional POSS particles into cross-linked epoxy does not cause a measurable change in its density, glass transition
temperature, or the CVTE. Furthermore, simulation results were used to characterize the aggregation of POSS particles in the
system. The nanofiller particles in systems containing 11, 20, and 30 mass/% POSS were found to form small clusters. The cluster-size
distribution of nanoparticles was also characterized for these systems. 相似文献
12.
Owing to their s2p5 electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH4, mimic the chemistry of halogens and readily form salts (e.g., Na+(AlH4)?), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage‐metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX4 (X=Cu, Ag, Au), these metal atoms may exhibit halogen‐like properties. By using density functional theory, we show that AlAu4 not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu4)2? (M=Na and K) and anionic (FAuF)? Au? (FAuF) range from 4.06 to 5.70 eV. Au‐based superhalogen anions, such as AlAu4? and AuF2?, have the additional advantage that they exhibit wider optical absorption ranges than their H‐based analogues, AlH4? and HF2?. Because of the catalytic properties and the biocompatibility of Au, Au‐based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu4, AlX4 (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom. 相似文献
13.
K. J. Rao 《Journal of Chemical Sciences》1984,93(3):389-406
The structure of real glasses has been considered to be microheterogeneous, composed of clusters and connective tissue. Particles
in the cluster are assumed to be highly correlated in positions. The tissue is considered to have a truly amorphous structure
with its particles vibrating in highly anharmonic potentials. Glass transition is recognized as corresponding to the melting
of clusters. A simple mathematical model has been developed which accounts for various known features associated with glass
transition, such as range of glass transition temperature,T
g, variation ofT
g with pressure, etc. Expressions for configurational thermodynamic properties and transport properties of glass forming systems
are derived from the model. The relevence and limitations of the model are also discussed.
Contribution No. 251 from Solid State and Structural Chemistry Unit. 相似文献
14.
Control of the optical properties of gel-derived oxide films containing fine metal particles is described. The duration of the aging of Si(OC2H5)4-derived sols and the amount of water for hydrolyzing Si(OC2H5)4 were found to greatly affect the size and the shape of Au particles formed in the silica matrix, and accordingly the optical absorption of the Au/SiO2 composite films. Employing dielectric media with high refractive indices like TiO2 was shown to shift the absorption peak of Au particles to longer wavelengths. Pd/TiO2 and Pt/TiO2 composite films showed absorption in the visible region. 相似文献
15.
Thierry Huillet 《Journal of mathematical chemistry》1998,24(1-3):187-221
Aggregation phenomena of elementary particles into clusters has received considerable attention during the past few decades. We adopt here a stochastic approach for the modeling of these phenomena. More precisely, we formulate the problem in the following dynamical setup: given a population of n discernible atoms partitioned into p discernible (model 1) or indiscernible (model 2) groups, how does a new atom eventually connect to any of these p groups forming up a new partition of n+1 atoms into a certain amount of clusters? Nucleation is said to occur when the inserted atom does not connect (it nucleates), whereas aggregation takes place if it does (clusters coalesce). Depending on this local “logic” of pattern formation, the asymptotic structure of groups can be quite different, in the thermodynamic limit N→∞. These studies are the main purpose of this work. Understanding these aggregation phenomena requires first to derive the fragment size distributions (that is, the number P of fragments, or clusters, and the number nm of size-m fragments with m fragments with constitutive atoms), as a function of the control parameter which is chosen here to be the average number of atoms 〈N〉. As 〈N〉 approaches infinity, we derive the study of these variables in the thermodynamic limit n → ∞. It is shown, making extensive use of combinatorics, that two regimes are to be distinguished: the one of weakly connected aggregates where nucleation dominates aggregation and the one of strongly connected aggregates where aggregation dominates nucleation. In the first (“diluted”) regime, the number of clusters P(n) always diverges as n → ∞, the asymptotic equivalent of which being under control in most cases. Large deviation results are shown to be available. Concerning N m(n), distinct behaviours are observed in models 1 and 2. In the second (“condensed”) regime, the number of groups P(n) and size-m groups N m(n) may converge in the thermodynamic limit, with a special role played by the geometric and Poisson distributions. The asymptotic variables become observable macroscopically. This work is therefore aimed toward a better understanding of the fundamentals involved in clusters' formation processes. 相似文献
16.
E. C. Honea J. S. Kraus J. E. Bower M. F. Jarrold 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):141-143
Size selected silicon clusters have been isolated in rare gas matrices and studied by optical absorption spectroscopy. The clusters were produced in a pulsed laser vaporization source, size selected with a quadrupole mass spectrometer and deposited at low energies into a cocondensed krypton matrix held at T<20 K. A comparison of the optical spectra of ten atom wide bands (Si25-Si35, Si35-Si45 and Si45-Si55) shows the general size evolution of the optical properties. Single cluster sizes have also been isolated and show somewhat sharper spectra than the bands. The measured spectra show similarities to spectra calculated using Mie theory and bulk optical constants. Cluster-cluster agglomeration was studied by evaporating the inert gas matrix. The results suggest that the clusters agglomerate into larger particles even under the mildest "soft landing" conditions. 相似文献
17.
Dr. Alessandro Longo Dr. Ewoud J. J. de Boed Dr. Nisha Mammen Dr. Marte van der Linden Prof. Dr. Karoliina Honkala Prof. Dr. Hannu Häkkinen Prof. Dr. Petra E. de Jongh Dr. Baira Donoeva 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(31):7051-7058
Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au–ligand species or ligand-free metallic Au0 clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Aun sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico-chemical properties. 相似文献
18.
Dr. Takuo Minato Prof. Dr. Masahiro Sadakane 《Angewandte Chemie (International ed. in English)》2023,62(41):e202309469
Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a “cationic metal glue strategy” for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4)Mn2Ln2(FeMn4)} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4} oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the “cationic metal glue strategy” would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively. 相似文献
19.
V. A. Nasluzov E. A. Ivanova-Shor A. M. Shor I. V. Yudanov N. Rösch 《Kinetics and Catalysis》2010,51(6):832-842
The review is devoted to the use of high-level quantum-chemical calculations by the density functional method for the simulation
of heterogeneous catalytic systems based on transition metals. The following problems are considered: (1) the development
of methods for simulating metal particles supported on the surfaces of ionic and covalent oxides; (2) the calculation of the
properties of individual transition metal atoms and small clusters adsorbed on the surfaces of MgO, α-Al2O3, γ-Al2O3, and various modifications of SiO2 and in the pores of zeolites; (3) the mechanisms of hydrogen activation and acrolein hydrogenation on the metallic and partially
oxidized surface of silver; and (4) the mechanism of formation of carbon residues upon the decomposition of methanol on nanosized
Pd particles. 相似文献