Clusters of Valence Electron Poor Metals—Structure,Bonding, and Properties

Metals in low oxidation states are capable of forming metal–metal bonds. An attempt has been made to classify the numerous phases and structures occurring in such metal-rich systems of valence electron poor metals in some sort of order from a rather general point of view. With this purpose in mind, clusters of these elements, their different types of interconnections, and their condensation via shared metal atoms, which finally leads to extended M? M bonded structures, are described. Interstitial atoms play an important role in stabilizing electron deficient clusters, and can actually lead to the loss of all M? M bonds. Surprising similarities emerge between apparently very different systems as the metal-rich oxides of alkali metals, the oxides, halides, and chalcogenides of d transition metals, and the halides and carbide halides of the lanthanoids.     

Promoting of non-transition metal alkylation with organyl halides in the presence of binary systems based on an organometallic compound and a transition metal compound: I. Hypothetical stepwise scheme and verification of the system efficiency

A hypothetical scheme has been proposed for the alkylation of non-transition metals with organyl halides in the presence of binary systems consisting of an organometallic compound and a transition metal compound. The scheme implies catalysis by transition metal atoms, small clusters, and subhalides adsorbed on the surface of metal to be alkylated. These particles are formed during the process as a result of interaction between the binary system components. The alkylation of commercial zinc powder with ethyl bromide has been used as a model reaction to demonstrate that the binary system ethylzinc bromide-copper(I) iodide is superior in its efficiency and experimental simplicity to all other examined methods for stimulation of the alkylation of elements with organyl halides yielding organometallic compounds.     

Alkalimetall-Cluster im Zeolith Y Darstellung,Eigenschaften, Reaktionen

Alkali Metal Clusters in Zeolite Y. Preparation, Properties, Reactions Alkali metal clusters (Type AB₃³⁺) were synthesized by reaction of alkali metal A (Li, Na, K, Rb, Cs) with the cations B (alkali, alkaline earth, and rare earth metals) of zeolite Y. The compounds were characterized by UV/VIS spectroscopy, oxidation by carbon oxides and organic halides, and adsorption of gases and polar molecules. The clusters are less reactive than the free alkali metals, the redox potential depends on the alkali metal as well as the cation of zeolite. Chemical interactions with typical ligands and with N₂, Ar, Kr, CO, CO₂, Benzene, and n-Hexane were observed. Reaction with ammonia leads to solvated electrons in zeolite's super-cage, stable up to 240 K.     

Promoting non-transition metal alkylation with organic halides in the presence of binary systems based on an organometallic compound and a transition metal compound: VIII. Selectivity of the binary systems action

Selectivity of action of binary systems based on an organometallic compound and a transition metal compound in a direct synthesis of organometallic compounds via alkylation of metals with organic halides has been considered. Study of the side reactions in the course of zinc and cadmium powders alkylation (gaseous hydrocarbons evolution) taken as an example has demonstrated that the increase in activity of the binary system components is accompanied by decrease in its selectivity. The intensity of the side reactions is steeply increased above certain temperature determined by the nature of the reactants and components of the binary system. The surface of the alkylated metal containing adatoms and small clusters of the transition metal promotes the side processes.     

贵金属及其掺杂团簇与甲烷反应研究进展

贵金属在甲烷活化与转化中呈现出优良的反应性。研究气态条件下贵金属物种与甲烷的反应,可以从分子水平上揭示凝聚相贵金属催化体系的活性位点与基元反应机理,为理性设计和改进催化剂提供理论基础。本文综述了贵金属原子、离子、团簇、氢化物、卤化物、氧化物、甲基配合物以及掺杂团簇活化、转化甲烷取得的新进展,并针对不同贵金属体系的甲烷活化机理展开讨论。     

Lanthanides as d Metals

Reduction of lanthanide trihalides with alkali metals along the route used by Klemm and Bommer leads to pure lanthanide metals. In closed Ta capsules at elevated temperatures, however, metal‐rich halides form which use the excess of Ln centered electrons for metal‐metal bonding. An overview of the extended d metal chemistry of lanthanides in binary, ternary and quaternary halides is presented. Consequences of the mutual interaction of d and f electrons are illustrated for selected magnetic and electrical properties.     

Vaporization and thermal decomposition of transition metal salts in flameless atomic absorption spectrometry with a carbon tube atomizer

Vaporization and thermal decomposition of Cr, Mn, Fe, Co, Ni and Cu salts were investigated by measuring the absorption spectra observed when aqueous solutions of these salts were heated in the carbon tube atomizer. Gaseous metal halides are vaporized in the atomizer at temperatures above 300–500° C. SO₂ and NO are produced by thermal decomposition of metal sulfates and nitrates, respectively. The vaporization of metal halides is also confirmed by the spectra for solutions of metals in hydrochloric acid and for mixtures of metal nitrates and ammonium halides.     

Preparation, characterization, and catalysis of mecro-catalysts

Because catalysis by metals is a surface phenomenon, many technological catalysts contain small (typically nanometre-sired) supported metal particles with a large fraction of the atoms exposed. Many reactions, such as hydrocarbon hydrogenations, are structure-insensitive, proceeding at approximately the same rates on metal particles of various sizes provided that they are larger than 1 nm and show bulk-like metallic behavior. But the catalytic properties are not known when metal particles become so small that their sizes are indium clusters consisting of several indium atoms. Here the catalytic behavior of precisely defined clusters of just four and six indium atoms on solid supports is shown. It is found that the Ir4 and Ir6 clusters differ in catalytic activity both from each other and from metallic Ir particles.     

Transition‐Metal‐Catalyzed CS Bond Coupling Reaction

Sulfur‐containing molecules such as thioethers are commonly found in chemical biology, organic synthesis, and materials chemistry. While many reliable methods have been developed for preparing these compounds, harsh reaction conditions are usually required in the traditional methods. The transition metals have been applied in this field, and the palladium‐catalyzed coupling of thiols with aryl halides and pseudo halides is one of the most important methods in the synthesis of thioethers. Other metals have also been used for the same purpose. Here, we summarize recent efforts in metal‐catalyzed C? S bond cross‐coupling reactions, focusing especially on the coupling of thiols with aryl‐ and vinyl halides based on different metals.     

Mechanism and removal of halide interferences in the determination of metals by atomic absorption spectrometry with electrothermal atomization

The effects of halides on the graphite-furnace atomic absorption determination of Al, Be, Sr, Cr, Mn, Ni, Co, Cu, Zn, Pb, Cd and Ag have been studied from the view-point of chemical reactions in solution, particularly in terms of the hard and soft acid and base concept. The harder halides interfere strongly with the harder metals, and the softer halides with the softer metals. This indicates that the halide interferences arise initially from metal—halide complex formation in solution; this was confirmed by an examination of halide concentration effects on the atomic absorption signal. The ammonium salt of EDTA is a most suitable additive for removal of halide interferences, because it prevents metal—halide complexation, and readily volatile ammonium halide is produced.     

Remarkable effect of alkali metal on polymerization of cyclic esters catalyzed by samarium-alkali metal multinuclear alkoxide clusters

The remarkable effect of alkali metal on catalytic reactivity of samarium-alkali metal multinuclear alkoxide clusters is systematically studied. Three samarium-alkali metal multinuclear alkoxide clusters are synthesized in high yield by the reaction of anhydrous SmCl(3) with different molar ratios of alkali metal alkoxide and MOH (M = Na or K) in tetrahydrofuran (THF). These clusters were fully characterized by elemental analysis, IR, (1)H NMR and single-crystal structural analysis. These clusters exhibited good catalytic activity for the ring-opening polymerization of ε-caprolactone (ε-CL), L-lactide (L-LA) and trimethylene carbonate (TMC). It is interesting to note that the catalytic activity is much influenced by the alkali metals of the clusters. For the polymerization of these cyclic esters, the catalytic activities all increase with the increase of the molar ratio of alkali metal to samarium metal.     

Structures and stabilities of 3d-transition metal-benzene organometallic clusters

In the gas phase, we have successfully synthesized organometallic clusters, M_n(benzene)_m (M=3d transition metal atoms), by using a laser vaporization method. The measurements of mass spectra and ionization energies (E_i) have revealed that the organometallic clusters can take two types of structures; layered sandwich structures (m = n + 1) and metal clusters saturatedly covered with benzenes. For early transition metals of Sc, Ti, and V, only the multiple decker sandwich structure clusters were preferentially produced, in which benzene and metal atoms are alternately piled up. For late transition metals of Co and Ni, the metal clusters saturatedly surrounded by benzenes were also produced as well as the sandwich clusters. Furthermore, the E_is of M₁(benzene)₂ (M = Sc-Ni) were systematically measured and their electronic properties will be discussed.     

New Forms and Functions of Tellurium: From Polycations to Metal Halide Tellurides

Metal chalcogenides and metal chalcogenide halides are distinguished by their structural diversity and by their very different physical properties. Therefore, the synthesis of novel compounds from this class is always a rewarding goal for the preparatively oriented solid-state chemist. Over the past few years, many syntheses and structural investigations have stimulated the field. The emphasis of the research has been placed on selenium-rich and tellurium-rich compounds, which are characterized by directed covalent bonds between the chalcogen atoms. Compounds with novel chalcogen polycations have also become accessible during the past few years by reacting the chalcogen elements with transition metal halides, or from chemical vapor deposition in the sense of chemical transport reactions. In these compounds, tellurium differs from its lighter homologues by a pronounced tendency towards greater covalence. This article attmepts to provide an overview of new developments in the field of compounds with chalcogen polycations and of metal chalcogenide halides, with an emphasis on compounds containing molybdenum and tungsten as the transition metals and tellurium as the chalcogen.     

New Transition Metal Clusters with Ligands from Main Groups Five and Six

In both physics and chemistry, increased attention is being paid to metal clusters. One reason for this attitude is furnished by the surprising results that have been obtained from studies of the preparation, structural characterization and physical and chemical properties of the clusters. Whereas investigations of cluster reactivity are at present generally limited to three- or four-membered clusters, successful syntheses of clusters with many more metal atoms have recently been designed. These substances occupy an intermediate position between solid state chemistry and the chemistry of metal complexes. This review presents a versatile method for synthesizing metal clusters: the reaction of complexes of transition metal halides with silylated compounds such as E(SiMe₃)₂ (E = S, Se, Te) and E′R(SiMe₃)₂ (R = Ph, Me, Et; E′ = P, As, Sb). Although some of the compounds thus formed have already been prepared by other routes, the method affords ready access to both small and large transition metal clusters with unusual structures and valence electron concentrations; a variety of reactions in the ligand sphere are also possible.     

Synthesis, structure and properties of metal nanoclusters

Metal nanoclusters have physical properties differing significantly from their bulk counterparts. Metallic properties such as delocalization of electrons in bulk metals which imbue them with high electrical and thermal conductivity, light reflectivity and mechanical ductility may be wholly or partially absent in metal nanoclusters, while new properties develop. We review modern synthetic methods used to form metal nanoclusters. The focus of this critical review is solution based chemical synthesis methods which produce fully dispersed clusters. Control of cluster size and surface chemistry using inverse micelles is emphasized. Two classes of metals are discussed, transition metals such as Au and Pt, and base metals such as Co, Fe and Ni. The optical and catalytic properties of the former are discussed and the magnetic properties of the latter are given as examples of unexpected new size-dependent properties of nanoclusters. We show how classical surface science methods of characterization augmented by chemical analysis methods such as liquid chromatography can be used to provide feedback for improvements in synthetic protocols. Characterization of metal clusters by their optical, catalytic, or magnetic behavior also provides insights leading to improvements in synthetic methods. The collective physical properties of closely interacting clusters are reviewed followed by speculation on future technical applications of clusters. (125 references).     

Monitoring the dissolution process of metals in the gas phase: reactions of nanoscale Al and Ga metal atom clusters and their relationship to similar metalloid clusters

Formation and dissolution of metals are two of the oldest technical chemical processes. On the atomic scale, these processes are based on the formation and cleavage of metal-metal bonds. During the past 15 years we have studied intensively the intermediates during the formation process of metals, i.e. the formation of compounds containing many metal-metal bonds between naked metal atoms in the center and ligand-bearing metal atoms at the surface. We have called the clusters metalloid or, more generally, elementoid clusters. Via a retrosynthetic route, the many different Al and Ga metalloid clusters which have been structurally characterized allow us to understand also the dissolution process; i.e. the cleavage of metal-metal (M-M) bonds. However, this process can be detected much more directly by the reaction of single metal atom clusters in the gas phase under high vacuum conditions. A suitable tool to monitor the dissolution process of a metal cluster in the gas phase is FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry. Snapshots during these cleavage processes are possible because only every 1-10 s is there a contact between a cluster molecule and an oxidizing molecule (e.g. Cl2). This period is long, i.e. the formation of the primary product (a smaller metal atom cluster) is finished before the next collision happens. We have studied three different types of reaction:(1) Step-by-step fragmentation of a structurally known metalloid cluster allows us to understand the bonding principle of these clusters because in every step only the weakest bond is broken.(2) There are three oxidation reactions of an Al13(-) cluster molecule with Cl2, HCl and O2 central to this review. These three reactions represent three different reaction types, (a) an exothermic reaction (Cl2), (b) an endothermic reaction (HCl), and (c) a kinetically limited reaction based on spin conservation rules (O2).(3) Finally, we present the reaction of a metalloid cluster with Cl2 in order to show that in this cluster only the central naked metal atoms are oxidized, and a smaller metalloid cluster results containing the entire protecting shell as the primary cluster.All the experimental results, supported by quantum chemical calculations, give a rough idea about the complex reaction cascades which occur during the dissolution and formation of metals. Furthermore, these results cast a critical light on many simplifying and generalizing rules in order to understand the bonding and structure of metal clusters. Finally, the experiments and some recent results provided by physical measurements on a crystalline Ga(84) compound build a bridge to nanoscience; i.e. they may be a challenge for chemistry in the next decades, since it has been shown that only with a perfect orientation of nanoscale metal clusters, e.g. in a crystal, can novel, unexpected properties (e.g. superconducting nanoscale materials) be obtained.     

ELECTRON TRANSFER REACTIONS OF METAL CARBONYL ANIONS

Abstract

Metal carbonyl anions exhibit one- and two-electron reactions. The two-electron processes involving transfer of groups (hydrogen, alkyl, and halogen) between metal centers are related to the nucleophilicity. The one-electron processes are primarily outer-sphere electron transfer for the metal carbonyl anions. These reactions are observed in the presence of oxidants such as coordination complexes, pyridinium salts, metal carbonyl dimers and metal carbonyl clusters. However, in contrast to organic reactions, the metal carbonyl anions may undergo inner-sphere electron transfer. Reactions of metal carbonyl anions of low nucleophilicity with metal carbonyl cations or halides are best interpreted as inner-sphere, one-electron transfer.     

Infrared spectra of the CH3-MX and CH2-MHX complexes formed by reactions of laser-ablated group 3 metal atoms with methyl halides

Reactions of laser-ablated group 3 metal atoms with methyl halides have been carried out in excess of Ar during condensation and the matrix infrared spectra studied. The metals are as effective as other early transition metals in providing insertion products (CH3-MX) and higher oxidation state methylidene complexes (CH2-MHX) (X = F, Cl, Br) following alpha-hydrogen migration. Unlike the cases of the group 4-6 metals, the calculated methylidene complex structures show little evidence for agostic distortion, consistent with the previously studied group 3 metal methylidene hydrides, and the C-M bond lengths of the insertion and methylidene complexes are comparable to each other. However, the C-Sc bond lengths are 0.013, 0.025, and 0.029 A shorter for the CH2-ScHX complexes, respectively, and the spin densities are consistent with weak C(2p)-Sc(3d) pi bonding. The present results reconfirm that the number of valence electrons on the metal is important for agostic interaction in simple methylidene complexes.     

Preparation of Organozinc and Organocadmium Compounds from the Metals and Alkyl Halides in the Presence of Stimulating Systems Based on a Derivative a Transition Metal and an Organometallic Compound

Full and mixed alkyl derivatives of zinc and cadmium were prepared from these metals and organic halides in the presence of stimulating systems necessarily containing a transition metal derivative and an organometallic compound capable of reducing this derivative under the process conditions. Such stimulating systems make it possible to introduce selectively organic halides (iodides, bromides, chlorides) into the reaction with zinc and cadmium to obtain the corresponding mixed organometallic compounds.     

Preparation and characterization of macroporous polystyrene resins containing ethynyl groups and transition metal acetylide complexes

Ethynylated polystyrene resins were prepared as functionalized polymer supports by the iodination reaction of macroporous polystyrene resins and reacted with transition metal diethynyl complex (Mt = Ni) and metal halides (Mt = Rh, Pd, and Pt) in a basic solvent using cuprous iodide as a catalyst to obtain macroporous polystyrene resins containing organotransition metals. The distribution of the metal acetylide complexes in the modified macroporous resins was determined by an electron probe microanalyzer. A gradient in the transition metal distribution was observed in any case of the modified resins. The stability of the organotransition metal complexes in the polymer matrix could be compared with a low molecular weight analogous complex quantitatively.