M4C9+(M = Ti, V): New gas phase clusters

New metal-carbon clusters, M₄C₉ ⁺ (M = Ti, V), generated using a combined thermal arc discharge evaporation set-up, have been studied with quadrupole mass spectrometry. Reactivities of these clusters have been investigated by means of association reactions with H₂O. Metal-carbon clusters of other compositions have also been studied. We speculate on the mechanism of formation of larger metal-carbon clusters.     

Adsorption of Propene on Neutral Gold Clusters in the Gas Phase

The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Au_n?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Au_n–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C₃H₆ on Au_n is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed.     

Doping Effects in Cluster‐Mediated Bond Activation

Gas‐phase investigations of judiciously doped oxide clusters permit to address fundamental challenges related to, for example, the low‐temperature oxidation of CO or the selective conversion of hydrocarbons. Modifying the size and composition of a free cluster in a controlled way enables the modification of local charge effects and of spin states, and spectroscopic studies in combination with computational work help to identify the active site of a catalyst and to unravel mechanistic details. Also, the interplay of the support material with the reactive part of a composite catalyst cluster can be addressed. Examples will be presented demonstrating how and why the gas‐phase reactivities of heteronuclear clusters, in comparison with their homonuclear counterparts, toward small, generally rather inert molecules can be increased, decreased, or not significantly affected.     

Binding of multiple SO2 molecules to small gold cluster anions (AuN−, AuNOH−, N = 1-8)

The binding of SO₂ on gas-phase gold cluster anions, Au_N⁻, and their hydroxide counterparts, Au_NOH⁻, have been studied using density functional theory combined with flow reactor/time-of-flight mass spectrometry techniques. SO₂ is adsorbed on all of the Au_N⁻ and Au_NOH⁻ clusters (N = 1-8) and the hydroxide clusters are more active than the bare anionic clusters. Successive additions of SO₂ molecules (up to four) have been analyzed. In all cases, anionic clusters are shown to bind multiple SO₂ molecules. Theoretical analyses are in agreement with the experimental results, showing that the addition of more than one molecule is thermodynamically favorable. Larger clusters do not necessarily absorb more molecules, as different SO₂ binding motifs on these clusters are present. These results provide important insight for the potential use of these anionic clusters as SO₂ hunters.     

Theory of measurement of gas-adsorption equilibria by rotational oscillations

The gas adsorbed on the inner surface of a highly porous material like activated carbon or zeolite can be measured by slow damped oscillations of a torsional pendulum. The physical principles and the theory of this method are outlined. Formulas are given relating the increase in mass due to adsorption to changes of the frequency and the logarithmic decrement of slow, damped rotational oscillations of the pendulum. Preliminary measurements of gas adsorption equilibria of nitrogen on activated carbon show that the ratio of the mass adsorbedm, to the mass of the adsorbentm ^s , can be determined by this method with mean absolute error |m/m ^s |0.04%.Dedicated to the memory of Joseph Kestin (1913–1993).     

Gas Phase Ion Chemistry of Transition Metal Clusters: Production, Reactivity, and Catalysis

This review focuses on the use of mass spectrometry to examine the gas phase ion chemistry of metal clusters. Ways of forming gas phase clusters are briefly overviewed and then the gas phase chemistry of silver clusters is discussed to illustrate the concepts of magic numbers and how reactivity can be size dependent. The chemistry of other bare and ligated metal clusters is examined, including mixed metal dimer ions as models for microalloys. Metal clusters that catalyze gas phase chemical reactions such as the oxidation of CO and organic substrates are reviewed. Finally the interface between nanotechnology and mass spectrometry is also considered.     

CuO/SiO2制备过程中吸附质相间分配比的调控及其对粒径影响的研究

吸附相反应过程中, 吸附层是反应的场所, 吸附质在吸附层和本体溶液中的分配对吸附层中的反应和粒子的形成、生长过程有重大影响. 通过定义相间分配比的概念, 研究了不同吸附质种类、不同温度和水量条件下吸附质相间分配比的变化规律. 采用XRD和TEM等手段考察了不同条件下制备所得样品的粒子大小、形貌等, 并与相间分配比的变化趋势相比较, 得到了相间分配比对粒径的调控规律. 研究发现不同吸附质在相间分配比上存在的差异导致了晶粒粒径的变化, Cu(OAc)₂的相间分配比大于NaOH的相间分配比, 因此以Cu(OAc)₂为吸附质制备得到的CuO粒子较小. 同时在常温(0～40 ℃)和低水量条件下时, 相间分配比的变化也是导致粒径变化的主要因素, 温度升高和水量增加均导致相间分配比变大进而导致粒径变小.     

Small Gold(I) and Gold(I)–Silver(I) Clusters by C−Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho-metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au₆L₄](X)₂ are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag₂O leads to gold–silver clusters [Au₄Ag₂L₄](X)₂. Oxo-trigold(I) species [Au₃O]⁺ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au₅], [Au₄Ag], and [Au₁₂Ag₄] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.     

Neue arsinidenverbrückte Mehrkern-Clusterkomplexe des Ag und Au. Die Kristallstrukturen von [Ag14(AsPh)6Cl2(PR3)8], (PR3 = PEt3, PMenPr2, PnPr3), [M4(As4Ph4)2(PR3)4], (M = Ag,PR3 = PEt3, PnPr3; M = Au,PR3 = PnPr3), [Au10(AsPh)4(PhAsSiMe3)2(PnPr3)6]

New Arsinidene-bridged Multinuclear Cluster Complexes of Ag and Au. The Crystal Structures of [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃, PMeⁿPr₂, PⁿPr₃), [M₄(As₄Ph₄)₂(PR₃)₄], (M = Ag, PR₃ = PEt₃, PⁿPr₃; M = Au, PR₃ = PⁿPr₃), [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] The reaction of AgCl with PhAs(SiMe₃)₂ in presence of tertiary phosphines (PR₃) leads to arsinidene-bridged silver clusters with the composition [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃ 1 , PMeⁿPr₂ 2 , PⁿPr₃ 3 ). Further it is possible to obtain the multinuclear complexes [Ag₄(As₄Ph₄)₂(PR₃)₄], (PR₃ = PEt₃ 4 , PMeⁿPr₂ 5 ). In analogy to that [PMe₃AuCl] reacts with PhAs(SiMe₃)₂ and PⁿPr₃ to form the compound [Au₄(As₄Ph₄)₂(PⁿPr₃)₄] 6 , which is isostructurell to 4 and 5 . The gold cluster [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] 7 was obtained from the same solution. The structures were characterized by X-ray single crystal structure analysis. (Crystallographic data see “Inhaltsübersicht”)     

苯乙炔吸附在金电极上的现场表面增强拉曼光谱研究

采用电化学现场表面增强拉曼光谱研究了苯乙炔在金电极上的吸附行为及表面反应过程. 负电位下拉曼光谱的变化表明, 苯乙炔分子的炔端碳与金属电极成键, 分子垂直吸附于金电极表面. 在所研究的负电位区间内, 分子在电极表面的吸附取向并未随电位发生改变. 电化学现场光谱研究表明, 苯乙炔分子随电位负移, 碳碳叁键被加氢还原. 通过对比苯乙烯的现场表面增强拉曼光谱发现, 在－0.6 V至－1.2 V的电位区间内, 苯乙炔经过中间步骤生成苯乙烯, 最终被完全加氢为苯乙烷.     

Platinum Group Metal Clusters: From Gas‐Phase Structures and Reactivities towards Model Catalysts

Transition‐metal clusters have long been proposed as model systems to study heterogeneous catalysts. In this Concept article we show how advanced spectroscopic techniques can be used to determine the structures of gas‐phase transition‐metal clusters and their complexes with small molecules. Combined with computational studies, this can help to develop an understanding of the reactivity of these catalytic models.