羰基原子簇化合物M3(CO)12(M=Fe,Ru,Os) 的激光解离研究

在自制的仪器上以脉冲激光溅射铁、钌、锇的三核羰基原子簇化合物,由原位质谱观察和分析溅射产生的正负离子. 比较了解离碎片及分布发现羰基锇原子簇化合物具有特殊的结构稳定性,它们不仅具有很强的金属键,而且锇与羰基分子还形成了很强的配位键. 铁和钌的原子簇在解离中脱落羰基配体,碎裂成双核以至单核的碎片离子. 而锇原子则先离解掉氧分子,形成新的C     

ⅥA族元素(S、S_e、T_e)桥连的钼铁混合金属羰基原子簇化合物的结构化学

本文总结了六种钼—铁混合金属羰基原子簇化合物的合成、结构类型和电子计数。从这些具有不同骨架构型的簇合物可以看出,主族元素—主族元素之间的相互作用对这类原子簇化合物的骨架构型变化和稳定性有着重要作用。     

具有活性的六核锇排状原子簇的合成、结构和反应性能研究

本文报道六核锇排状平面原子簇的合成和活化。三核锇活性原子簇[Os_3(CO)_(10)(MeCN)_2]在PdCl_2催化作用下发生偶联反应,生成具有活性的六核锇排状原子簇[Os_6(CO)_(20)(MeCN)]和[Os_6(CO)_(19)(MeCN)_2]。用氧化三甲胺(Me_3NO)对活性原子簇中羰基配位基进行多重活化,获得一系列具有活性的六核锇排状原子簇[Os_6(CO)_(21-n)(MeCN)_n](n=1—5)及其相应的配位体取代反应产物[Os_6(CO)_(21-n)(P(OMe)_3)_n](n=1—5)。并通过红外光谱、核磁共振波谱和质谱等数据对上述排状原子簇进行结构表征,同时就其排状平面结构和反应性能特点进行讨论。     

一些金属原子簇羰基化合物的流变性及其电子结构的EHMO研究

近年来,关于过渡金属原子簇化合物的研究工作发展很快。这类化合物的通式是 M_pL_q,其中 M_p 是 p 个以 M—M 键相结合的金属原子所形成的原子簇,L 则是与原子簇 M_p 相结合的配位体,如羰基、卤素离子、CN~-、膦等。这类化合物有许多特点,金属原子簇具有介于单原子和金属微晶之间的一种过渡型结构。配位体和被金属表面吸附了的分子或离子相似。由     

还原性的类立方烷型金属有机原子簇[M_4(μ~3-Se)_4(η-C_5H_4R)_4](M=Mo,R=Pr~i;M=Cr,R=Me)的合成、晶体结构和电子性质

类立方烷型金属原子簇化合物M_4E_4(M为过渡金属,E为硫属元素)的研究长期以来受到重视,其主要原因有二:(1)一些类立方烷型金属原子簇(如Fe_4S_4及Fe-Mo-S原子簇)在生物体系(如固氮酶、铁氧还蛋白)中有重要意义;(2)由于可以方便地对M或E作系列性的改变,因而M_4E_4成为研究原子簇化合物的电子结构及检测各种有关的理论假设的重要模型化合物。     

环烯丙醇的四氧化锇氧化反应

四氧化锇转换烯烃为邻二醇是熟知的反应,文献也有报道链状的烯丙醇被四氧化锇氧化为相应的三醇化合物。本文报道,当环烯丙醇被四氧化锇氧化时。则随烯烃空间障碍的不同而结果不同。空间隙碍比较大的环烯丙醇得到羟基被氧化的α、β不饱和羰基化合物;空间障碍小的则主要产物为相应的三醇化合物;而具有中等程度空间障碍的环烯丙醇得到二类竞争性反应产物,即相应的三醇化合物和α、β不饱和羰基化合物。     

还原性的类立方烷型金属有机原子簇[M4(μ^3-Se)4(η-C5H4R)4](M=Mo, R=Pr^i;M=Cr, R=Mc)的合成, 晶体结构和电子性质

H2Se与Cr(η-C5H4Me)2的反应产生了得率高达90%的原子簇化合物[Cr4(μ^3-Se)4(η-C5H4Me)4], 而LiSeH与Mo2(η-C5H4Pr^i)2(μ-Cl)4的反应则产生了其它的簇状化合物[Mo4(μ^3-Se)4(η-C5H4Pr^i)4], 它们都是通过元素分析和H核磁共振谱的研究, X射线单晶体结构分析加强了金属有机原子簇的还原性结构, 循环伏安法数据表明原子簇在溶液中的还原电极电位越低, 其气相第一电离势一般也越小, 光电子谱法研究也表明这些原子簇都具富电子的。     

过渡金属羰基簇的成键规则

原子簇化合物在性质、结构和成键方式等方面的特殊性,引起了合成化学、结构化学、催化化学及理论化学界的浓厚兴趣,且具有日益广阔的应用前景。对于其成键规律的研究,继Wade等提出的多面体骨架电子对理论之后,已有不少工作。本文系统研究了过渡金属羰基型原子簇化合物的结构特点,提出了确定9N-μ规则中μ值的四项条款,并用以解释了许多种过渡金属羰基簇化合物。讨论了它们的电子结构、反应性、成键特点等性质。由此还可     

羰基簇成键规则BMO=9N—B_计的导出

朱龙根等人指出羰基簇的价电子数,除双核和三核与可能具有的M—M多重键有关外,其余皆取决于成簇原子数及几何特点。认为金属原子簇的骨架结构本身就决定了原子簇化合物的成键轨道数。提出若N个过渡金属原     

低热固相反应合成Mo(W)-Cu(Ag)-S簇合物

本文对现有中,高温固相化学反应方法合成含硫原子簇化合物作了探讨,介绍了我们实验室用低热温度固相反应合成原子簇化合物的新方法,总结了几年来我们用此法合成的S-Mo(W)-Cu(Ag)原了簇化合物,并测定结构二十余个,其中包括了含有二十个金属原子的大核原子簇化合物[(n-Bu)_4N]_4[Mo_8Cu_(12)S_(32)]。     

RP-Bridged Metal Carbonyl Clusters: Synthesis,Properties, and Reactions

Metal carbonyl clusters possess a complicated chemistry that is only beginning to be understood. One of the main current goals in this area is thus an understanding of their reactivity. This article describes the syntheses and reactions of clusters that contain metal carbonyl fragments bridged by a main-group element. But what is the sense of making such clusters still more complicated by the incorporation of main-group elements? The example of μ₃-bridged carbonyl clusters will serve to show that the main-group element plays an important role in the study of reaction paths; it holds the metal carbonyl fragments together even when the bonds between them are broken in the course of a reaction. Trinuclear μ₃-bridged clusters prove to be small enough to allow the analysis of typical cluster reactions (such as the reversible breaking of metal-metal bonds) in terms of single reaction steps. They are also large enough to provide surprises by their multifaceted reactivity. It will be shown that a detailed study of trinuclear RX-bridged metal carbonyl clusters (X ? N, P, As, Sb, Bi)—a very small part of carbonyl cluster chemistry—can lead to a better understanding of the general reaction principles involved.     

Analysis of low oxidation state transition metal clusters by laser desorption/ionization time-of-flight mass spectrometry

A variety of homonuclear and heteronuclear transition metal carbonyl clusters have been analyzed by ultraviolet laser desorption/ionization time-of-flight mass spectrometry. The spectra were recorded in negative and positive ion modes, using both linear and reflective techniques. A range of different clusters based on different nuclearities, geometries, and ligand types, which include hydrides, phosphines, nitriles, and cyclopentadienyl ligands and naked main group atoms, were studied. These experiments have allowed us to construct a detailed picture of the technique for the analysis of transition metal carbonyl clusters and their derivatives. In general, extensive reactions are observed, cluster aggregation reactions in particular, and from a comparison of the spectra obtained, some mechanistic inferences concerning the aggregation processes have been drawn.     

Laser Desorption Ionization Versus Electrospray Ionization Mass Spectrometry: Applications in the Analysis of Cluster Anions

Mass spectra of transition metal carbonyl cluster anions were recorded using laser desorption ionization time-of-flight (LDI-TOF) and electrospray ionization (ESI) techniques. The LDI spectra generally contain peaks corresponding the intact cluster together with extensive CO loss fragments ions whereas the ESI spectra exhibit peaks corresponding the intact cluster together with few (if any) CO loss fragment ions. The parameters of both techniques can be modified to vary the extent of fragmentation. In all cases no fragmentation of the metal core is observed. Overall, ESI is a more informative method for the analysis of these types of cluster anions.     

激光作用磷化铟所产生的负离子质谱及其分析

以激光蒸发结合超声分子束膨胀,近年来已成为产生与研究原子簇的一种重要手段。在以这一方式产生的Ga_xAs_y的光电离质谱中,发现含奇数个原子的簇离子的信号强度相对较高。最近我们在自制的装置上,于高真空中直接以脉冲激光作用于GaAs、GaP、InP等多种半导体材料,在所记录的负离子质谱中也都观察到类似的奇强偶弱的现象,其中尤以In_xP_y~-最为显著。实验用的激光离子源飞行时间质谱计的构造已有另文详细介绍。该装置通过朝相反方向分别加速正负离子而可同时记录激光等离子体的正负离子质谱。实验采用Nd~(3+):YAG激光器的调Q倍频输出(532nm),聚焦后作用于样品表面的激光功率密度约为10~8W·cm~(-2)。质谱计的加速电压1kV,正负离子的无场漂移长度约1.15m,数据的模数转换速度为2×10~7s~(-1)。实验所用的磷化铟是片状的高纯度半     

Electronic and Geometric Structure of Bimetallic Clusters: Density Functional Calculations on [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and [Ag(13){Fe(CO)(4)}(8)](n)(-) (n = 0-5)

The results of all-electron density functional calculations on the bimetallic cluster compounds [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and on the corresponding naked species M(4)Fe(4) are reported. The trends within the triad have been investigated. The bare metal clusters exhibit a strong magnetization which is quenched on addition of CO ligands. The bonding in the bare clusters is different for the silver derivative compared to that of copper and gold, resulting in comparatively weaker Ag-Fe and Ag-Ag bonds. This can be rationalized in terms of the different d-sp mixing, which for Cu and Au is larger than for Ag. Relativistic effects act to increase the 4d-5s mixing in Ag and to strengthen the intermetallic bond with Fe. In the carbonylated clusters a charge transfer from the metal M (M = Cu, Ag, or Au) to the Fe(CO)(4) groups occurs so that the atoms M can be considered in a formal +I oxidation state, rationalizing the nearly square-planar geometry of the metal frame. In fact, the local coordination of the M atoms is almost linear, as expected for complexes of M(I). The addition of extra electrons results in a stabilization of the clusters, indicating the electron-deficient nature of these compounds. Similar features have been found for the largest cluster synthesized so far for this class of compounds, [Ag(13){Fe(CO)(4)}(8)](n)(-), (n = 0-5). The nature and localization of the unpaired electron in the tetraanion is also discussed.     

Characterization of Ti(6)O(4)(O(2)C(4)H(5))(8)(OCH(2)CH(3))(8) by electrospray time of flight mass spectrometry

A titanium oxide molecular cluster prepared by hydrolysis of titanium tetraethoxide in the presence of methacrylic acid, can be characterized by electrospray time of flight mass spectrometry (ESMS-TOF). The chemistry of such systems is not well known and ESMS is a powerful technique for studying the reactions of clusters in solution. The fingerprint of the cluster fragmentation suggests formation of Ti(x)O(y) core fragments that represent commonly observed structural constructs in bulk titanium oxide metallates. The fragmentation steps provide insight into the hydrolytic conversion of this molecular sol gel intermediate into bulk TiO(2). While MS has been applied to the study of metal alkoxide hydrolysis mechanisms, mass spectra of isolated individual titanium oxide clusters have not previously been reported.     

Mass distribution of cluster ions produced from laser ablation of metal-composite-oxides Y-M-Cu-O (M=Ba,Sr, Ca,Mg)

Laser ablation of YMCuO metal-composite-oxides (M=Ba, Sr, Ca, Mg) in high vacuum produced cluster ions with various sizes and compositions. Mass spectra of the cluster ions were recorded by a home-built time-of-flight (TOF) mass spectrometer and the mass distributions were analyzed by a statistical model. For YBa₂Cu₃O_7?x (YBCO) high-Tc superconducting samples, six series of cluster ions were observed. Replacement of barium in the metal-composite-oxide sample with other alkaline earth metal, such as strontium, calcium, or magnesium, not only removed the superconductivity, but also changed the compositions and distributions of the laser generated cluster ions. For instance, copper was only found in the compositions of cluster ions generated from YBCO sample. From comparison of the experimental results, interactions among components of the metal-composite-oxides and the function of alkaline earth metal in superconducting material were discussed.     

Laser desorption/fourier transform mass spectra of poly(phenylene sulfide), polyaniline,poly(vinyl phenol), polypyrene,and related oligomers: Evidence for carbon clusters and feasibility of physical dimension measurement

Laser desorption/Fourier transform mass spectra of poly(phenylene sulfide), polyaniline, poly(vinyl phenol), polypyrene, poly(p-phenylene), poly(1-methyl-2,5-pyrrolylene), poly(1-phenyl-2,5-pyrrolylene), and poly(2,5-thienylene) are compared. Poly(phenylene sulfide) fragments at C? S bonds during analysis, but rearrangement is minor. Evidence is found for dibenzothiophene moieties within the polymer chains. Unambiguous determination of the structure of polyaniline is not possible. Rearrangement appears to accompany chain scission. Completely aromatic polymers do not undergo similar reactions during analysis. Species with more carbons than can be accounted for by an integer multiple of six-membered rings arise from side reactions during dehydrocoupling of aromatic monomers. Carbon clusters, which are observed in the spectra of some aromatic polymers, appear to arise from laser volatilization and multiphoton ionization of large polynuclear components that are formed during synthesis. Negative ions of about 40–120 carbons and positive ions with about 120–400 atoms are detected. The results also suggest that the physical dimensions of some polymer molecules might be measured by Fourier transform mass spectrometry.     

Infrared Spectra,Structures and Bonding of Binuclear Transition Metal Carbonyl Cluster Ions

Binuclear transition metal carbonyl clusters serve as the simplest models in understanding metal-metal and ligand bonding that are important organometallic chemistry catalysis. Binuclear first row transition metal carbonyl ions are produced via a pulsed laser vaporization/supersonic expansion cluster ion source in the gas phase. These ions are studied by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. Density functional theory calculations have been performed on the geometric structures and vibrational spectra of the carbonyl ions. Their geometric and electronic structures are determined by comparison of the experimental IR spectra with the simulated spectra. The structure and the metal-metal and metal-CO bonding of both saturated and unsaturated homonuclear as well as heteronuclear carbonyl cluster cations and anions are discussed.     

Structure of molybdenum and tungsten sulfide M(x)S(y)+ clusters: experiment and DFT calculations

A combination of experiment and density functional theory was used to investigate the energetics of CO adsorption onto several small M(x)S(y)(+) (M = Mo, W; x/y = 2/6, 3/7, 5/7, 6/8) clusters as a probe of their atomic and electronic structure. Experimentally, tandem mass spectrometry was used to measure the relative yields of M(x)S(y)(+)(CO)(n) cluster adducts formed by collisions between a beam of mass-selected M(x)S(y)(+) cluster ions and CO molecules in a high-pressure collision cell (hexapole ion guide). The most probable M(x)S(y)(+)(CO)(n) adducts observed are those with n < or = x, that is, only one CO molecule bound to each metal site. The notable exception is the M(5)S(7)(+) cluster, for which the n = 6 adduct is found to have nearly the same intensity as the n = x = 5 adduct. Density functional calculations were used to search for the lowest energy structures of the bare M(x)S(y)(+) clusters and to obtain their relative stability for sequential CO binding. The calculated trends in CO binding energies were then compared to the experimental adduct distributions for assigning the ground-state structures. In this way, it was possible to distinguish between two nearly isoenergetic ground-state isomers for the M(2)S(6)(+) and M(3)S(7)(+) clusters, as only one isomer gave a calculated CO stabilization energy trend that was consistent with the experimental data. Similar comparisons of predicted and observed CO adsorption trends also provide evidence for assigning the ground-state structures of the M(5)S(7)(+) and M(6)S(8)(+) clusters. The latter contain metallic cores with most of the sulfur atoms bonded along the edges or in the faces of the metal core structure. The n = 6 and 7 adducts of M(5)S(7)(+) are predicted to be more stable than the n = x = 5 adduct, but only the n = 6 adduct is observed experimentally. The DFT calculations show that the n = 7 adduct undergoes internal bond breaking whereas the n = 6 framework is stable, albeit highly distorted. For the M(6)S(8)(+) cluster, the calculations predict that the two lowest energy isomers can bind more than six CO molecules without fragmentation; however, the apparent binding energy drops significantly for adducts with n > 6. In general, the ability of these small M(x)S(y)(+) clusters to bind more CO molecules than the number of metal atoms is a balance between the gain in CO adsorption energy versus the strain introduced into the cluster structure caused by CO crowding, the consequences of which can be fragmentation of the M(x)S(y)(+)(CO)(n) cluster adduct (n > x).