Metal-cluster compounds: Model systems for nanosized metal particles

Meta-cluster compounds can be exploited advantageously to study the evolution, with increasing size of the molecules of the physical properties of metal clusters from molecular to bulk-metal behavior. The metal-cluster molecules are well-defined, stoichiometric, chemical compounds. The molecules consist of a metal core of a variable number of atoms, surrounded by a shell of ligand atoms or molecules. Depending on the compound, the type of metal atom may be varied, whereas the core size can be changed from a few up to several thousands of atoms. Accordingly, these materials provide excellent model systems for monodisperse metal particles, embedded in a dielectric matrix, and can be investigated by the well-known experimental techniques of solid-state physics. © 1998 John Wiley & Sons, Ltd.     

Chemi-Inspired Silicon Allotropes—Experimentally Accessible Si9 Cages as Proposed Building Block for 1D Polymers, 2D Sheets,Single-Walled Nanotubes,and Nanoparticles

Numerous studies on silicon allotropes with three-dimensional networks or as materials of lower dimensionality have been carried out in the past. Herein, allotropes of silicon, which are based on structures of experimentally accessible [Si₉]⁴⁻ clusters known as stable anionic molecular species in neat solids and in solution, are predicted. Hypothetical oxidative coupling under the formation of covalent Si–Si bonds between the clusters leads to uncharged two-, one- and zero-dimensional silicon nanomaterials not suffering from dangling bonds. A large variety of structures are derived and investigated by quantum chemical calculations. Their relative energies are in the same range as experimentally known silicene, and some structures are even energetically more favorable than silicene. Significantly smaller relative energies are reached by the insertion of linkers in form of tetrahedrally connected Si atoms. A chessboard pattern built of Si₉ clusters bridged by tetrahedrally connected Si atoms represents a two-dimensional silicon species with remarkably lower relative energy in comparison with silicene. We discuss the structural and electronic properties of the predicted silicon materials and their building block nido-[Si₉]^4– based on density functional calculations. All considered structures are semiconductors. The band structures exclusively show bands of low dispersion, as is typical for covalent polymers.     

Metal deposits on well-ordered oxide films

Metal oxide interfaces, metal coatings or dispersed metals on oxide supports play an important part in many technological areas. Nevertheless, there is still a lack of fundamental knowledge about the essential properties of thin metal films and small metal particles on oxide supports, although a deeper understanding could help to improve the electronic, mechanical or catalytic performance of such systems. In the past, a number of different approaches have been proposed and explored aiming at the preparation of suitable model systems. In this review, we discuss the possibility to use thin, well-ordered oxide films as supports for the study of deposited metal particles. This approach offers the advantage to permit the unrestricted application of all experimental methods, which rely on a good electrical or thermal conductivity of the sample, like PES, LEED, STM or TDS. With the help of several examples taken from our own work on a thin alumina film, we show that it is feasible to characterise such systems on a microscopic level with respect to all relevant structural, electronic and adsorption properties. In this way, correlations between these features can be established helping to understand the particular chemistry and physics of small metal aggregates.     

簇合物Mo2X4(X＝S,O)电子结构和光谱性质的Ab Initio研究

在abinitio水平上对含cis/trans-MO₂S₄核和含Mo₂O₄核簇合物的电子结构进行了研究.对钼原子选取和构造了一组适合于含Mo-Mo金属键的双核钼簇合物从头算的(4s4p2d)基组,利用该基组并结合自然键轨道(NBO)方法,对含上述簇胳的3个簇合物的电子结构进行了研究,并与相应的钨簇合物进行了比较.     

铁-硒二元团簇离子的产生和紫外光解

用激光直接溅射的方法产生了铁－硒二元团簇,并用串级飞行时间质谱仪研究了二元团簇的组份和光解规律。一组谱中组成ＦｅｎＸＳｅｎ＾＋,ＦｅｎＳｅｎ－１＾＋和ＦｅｎＳｅｎ＾－、ＦｅｎＳｅｎ＋１＾－是二元团簇的结构骨架和稳定组份。团簇正离子ＦｅｎＳｅｎ＾＋的紫外光解结果表明,光解产物主要为一级谱中丰度较大的离子,用密度泛函方法（ＤＦＴ）优化了Ｆｅ２Ｓｅ２＾＋的几何结构,并计算了其光解通道,能较好地解释光解的     

Synthesis of ferrocenylacetylide derivatives of gold-ruthenium and gold-osmium clusters. Crystal structures of M3(AuPPh3)(C≡CFc)(CO)9 (M=Ru or Os; Fc is ferrocenyl)

The synthesis and crystal structures of the clusters M₃(AuPPh₃)(C≡CFc)(CO)₉ (M=Ru,3a; or M=Os,3b) are described. Compound3a was synthesized by deprotonation of Ru₃H(C≡CFc)(CO)₉ under the action of KOH/EtOH followed by treatment of the anionic complex [Ru₃(C≡CFc)(CO)₉]⁻ with chloro(triphenylphosphine)gold. Compound3b was prepared by the reaction of Os₃(CO)₁₀(NCMe)₂ with FcC≡CAuPPh₃, which was synthesized by the reaction of FcC≡CNa with ClAuPPh₃. The pentanuclear cluster Ru₄(AuPPh₃)(C≡CFc)(CO)₁₂ (4a), which was prepared by the reaction of3a with Ru₃(CO)₁₂, was characterized by spectral methods. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1295–1299, July, 2000.     

Influence of covalence and anion symmetry on the structure of small metal hydroxide clusters: Sodium versus silver hydroxide

An ab initio study of the Na_n(OH)_n, Na_n(OH)_n-1 ⁺, Ag_n(OH)_n, and Ag_n(OH)_n-1 ⁺ clusters with n up to four is presented. The results of this study show that, in accordance with experimental observations, the sodium hydroxide clusters are almost purely ionic, while the Ag-O bond exhibits a significant covalent character. The perturbation caused by the non-spherical OH^- group relatively to an atomic anion, as well as the influence on structures and energies of the covalent character of the metal-oxygen bond are determined. The appearance of metal-metal bonds in the silver hydroxide clusters is also discussed. Finally, the theoretical results obtained on the Na-OH clusters are compared to experimental results available on the dissociation of the Na_n(OH)_n-1 ⁺ clusters. Received 9 August 1999 and Received in final form 1st December 1999     

Spontaneous alloying of tin atoms into nanometer-sized gold clusters and phase stability in the resultant alloy clusters

Alloying behavior and phase stability has been studied in situ by transmission electron microscopy using clusters in the Au-Sn system. When tin atoms are vapor-deposited onto nm-sized gold clusters, rapid dissolution of tin atoms into gold clusters takes place and as a result Au-rich solid solution, amorphous-like Au-Sn alloy and AuSn compound clusters are formed depending upon the concentration of tin. The remarkable enhancement of solubility has been observed in Au-rich solid solution and AuSn compound. It becomes more difficult to form two phases in the interior of individual clusters even if the composition of alloy clusters falls in the two-phase region in the phase diagram for the bulk alloy and as a result amorphous-like phase is stabilized in nm-sized Au-Sn alloy clusters. Received 2 August 1999 and Received in final form 8 November 1999     

Electrodynamics of Noble Metal Nanoparticles and Nanoparticle Clusters

In this paper we examine the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surface-enhanced Raman (SER) intensities. The particles and clusters are chosen to be representative of what has been studied in recent work on colloids and with lithographically prepared particles. These include spheres, spheroids, truncated tetrahedrons, and clusters of two or three of these particles, with sizes that are too large to be described with simple electrostatic approximations but small compared to the wavelength of light. The electrodynamics calculations are mostly based on the discrete dipole approximation (DDA), which is a coupled-finite element approach which produces exact or nearly exact results for particles of arbitrary size and shape if fully converged. Mie theory results are used to study the validity of the DDA for spherical particles, and we also study the validity of the modified long wavelength approximation (MLWA), which is based on perturbative corrections to the electrostatic limit, and of the single dipole per particle approximation (SDA). The results show how the dipole plasmon resonance properties and the electric field contours around the particle vary with particle shape and size for isolated particles. For clusters of particles, we study the effect of interparticle spacing on plasmon resonance characteristics. We also show that the quadrupole resonance is much less sensitive to particle shape and interparticle interactions than the dipole plasmon resonance. These results provide benchmarks that will be used in future comparisons with experiment.     

Site-selective carbonyl substitution in the mixed-metal cluster anion [H2Ru3Ir(CO)12]: synthesis and characterization of phosphine, phosphite, arsine and stibine derivatives

The reaction of the mixed-metal carbonyl cluster anion [H₂Ru₃Ir(CO)₁₂]⁻ with PPh₃, PMe₃, P(OPh)₃, AsPh₃ or SbPh₃ leads to the mono-substituted derivatives [H₂Ru₃Ir(CO)₁₁L]⁻ (L=PPh₃ 1, L=PMe₃ 2, L=P(OPh)₃ 3, L=AsPh₃ 4, L=SbPh₃ 5). Protonation of the anions 1–5 gives the neutral trihydrido derivatives H₃Ru₃Ir(CO)₁₁L (L=PPh₃ 6, L=PMe₃ 7, L=P(OPh)₃ 8, L=AsPh₃ 9, L=SbPh₃ 10). All new tetranuclear clusters invariably show a tetrahedral arrangement of the Ru₃Ir skeleton, as predicted for 60 e systems. The ligand L is coordinated to one of the ruthenium atoms, except in the case of L=PMe₃ where two substitution isomers are observed. While the anionic isomers [H₂Ru₃Ir(CO)₁₁(PMe₃)]⁻ (2) could not be separated, the corresponding neutral isomers H₃Ru₃Ir(CO)₁₁(PMe₃) (7) could be resolved by thin-layer chromatography. In isomer 7a, the phosphine ligand is coordinated to one of the ruthenium atoms, whereas in isomer 7b the PMe₃ ligand is bonded to the iridium atom. The molecular structures of 1, 7b, 8 and 9 were confirmed by a single-crystal X-ray structure analysis.