Fe(0)(CO)3(Ph2Ppy)2Mn+Cln中金属-金属成键的光谱研究

本文研究了七个以反式二（二苯基膦吡啶）－三羰基铁为三齿配体的过渡金属双核配合物，将Ｊｏｒｇｅｎｓｅｎ建议的处理电荷转移光谱的方法推广处理ＭＭＣＴ跃迁，通过光学电负性的计算取得金属－金属成键的证据。由Ｒａｍａｎ光谱羰基伸缩振动频率的蓝移进一步支持这类化合物中存在金属－金属成键相互作用的推断。     

Reflections on osmium and ruthenium carbonyl compounds

The development of transition metal cluster chemistry is traced from the early discoveries of metal-metal bonded systems through to some recent developments made in the area of high nuclearity osmium and rutherium cluster carbonyls. Emphasis is placed on developments made in the physical techniques used to establish the structures of the cluster complexes in the solid state and in solution. Recent developments in synthetic methods which lead to “rational” cluster synthesis are described, and the electron counting rules used to rationalise the observed structures of carbonyl clusters are reviewed. New high nuclearity cluster structures are described, and emphasis is placed on the ability of these systems to undergo reversible redox chemistry without the metal frameworks rearranging. This contrasts the situation observed for low nuclearity clusters, and illustrates the potential of the higher nuclearity clusters to act as electron sinks.     

Binuclear cyclopentadienylmetal cyclooctatetraene derivatives of the first row transition metals: effects of ring conformation on the bonding of an eight-membered carbocyclic ring to a pair of metal atoms

Binuclear Cp(2)M(2)(μ-C(8)H(8)) derivatives have been synthesized for M = V, Cr, Co, and Ni and have now been studied theoretically for the entire first row of transition metals from Ti to Ni. The early transition metal derivatives Cp(2)M(2)(μ-C(8)H(8)) (M = Ti, V, Cr. Mn) are predicted to form low-energy cis-Cp(2)M(2)(μ-C(8)H(8)) structures with a folded C(8)H(8) ring (dihedral angle ～130°) and short metal-metal distances suggesting multiple bonding. These predicted structures are close to the experimental structures for M = V, Cr with V≡V and Cr≡Cr bond lengths of ～2.48 and ～2.36 ?, respectively. The middle to late transition metals form trans-Cp(2)M(2)(μ-C(8)H(8)) structures (M = Mn, Fe, Co, Ni) with a twisted μ-C(8)H(8) ring and no metal-metal bonding. The hapticity of the central μ-C(8)H(8) ring in such structures ranges from five for Mn and Fe to four for Co and three for Ni and thus depend on the electronic requirements of the central metal atom. This leads to the favored 18-electron configuration for both metal atoms in the singlet Fe, Co, and Ni structures but only 17-electron metal configurations in the triplet Mn structure. In addition, the late transition metals form trans-Cp(2)M(2)(μ-C(8)H(8)) structures (M = Fe, Co, Ni), with the tub conformation of the μ-C(8)H(8) ring functioning as a tetrahapto (M = Fe, Co) or trihapto (M = Ni) ligand to each CpM group. A μ-C(8)H(8) ring in the tub conformation also bonds to two CpFe units as a bis(tetrahapto) ligand in both singlet and triplet cis-Cp(2)Fe(2)(μ-C(8)H(8)) structures.     

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.     

过渡金属羰基簇合物的键价计算和分析

本文运用原子簇化合物键价计算公式 ,对过渡金属羰基簇合物成键情况进行了分析 ,利用金属键轨道数 ,价非键轨道数和金属配体成键轨道数计算簇合物价轨道总数 .计算结果表明 :簇合物价轨道总数与金属键轨道数成线性关系 ,BT=9N -Bn.对于一般簇合物其价轨道总数与Lauher的EHMO计算结果 ,与唐敖庆的结构拓扑规则一致 ,对于反常的高核簇合物其价轨道总数与按化学式计算的 1/ 2VE相吻合     

Exchange coupling through diamagnetic [Fe(CO)4]2- bridging ligands in a xenophilic cluster

The electronic structure of so-called 'xenophilic' clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn(2)(thf)(4)(Fe(CO)(4))(2) is best described as an exchange-coupled Mn(II)(2) dimer, the closed-shell organometallic [Fe(CO)(4)](2-) fragments acting simply as bridging ligands. The high-spin configuration of the Mn(II) ions leads to single occupation of the Mn-Fe σ* orbitals and therefore substantially weaker metal-metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (J(calc) = -44 cm(-1)), leading to the measured effective magnetic moment of ~5 μ(B) at 300 K, considerably lower than the limiting value of 8.37 μ(B) for two uncoupled S = 5/2 Mn(II) centres.     

Two-dimensional correlation spectroscopic studies on coordination between carbonyl group of butanone and metalions

Two dimensional asynchronous spectra were used to characterize coordination between carbonyl group of butanone and metal ions by using an approach proposed in our recent paper.Spectral variation of n-π~*transition band of carbonyl group is used to probe the coordination even if metal ions does not possess any characteristic peak in spectra.Experimental results indicate that Ca~(2+) and Al~(3+) show considerable ability to coordinate with the carbonyl group of butanone and bring about spectral variation of the n-π~*transition band,which is manifested by cross peaks in 2D asynchronous spectra.     

Electronic Structure of [Ta(5)(NH)(4)Cl(17)](6-): A Cluster with a Distorted Square Pyramidal Ta(5) Core

We report approximate molecular orbital calculations on the [Ta(5)(NH)(4)Cl(17)](6-) cluster synthesized by Simon and Meyer. The cluster is based on a "flattened" square pyramid of tantalum atoms, basal bridging imides, and terminal chlorides. This cluster was of interest to us due to the unusual presence of imide ligands, the distorted nature of the metal core, and the possible resemblance to B(5)H(9). Our calculations indicate that metal-metal bonding is limited to Ta(apical)-Ta(basal) bonding, with no significant bonding between the basal metal atoms. The imide ligands, which bridge the base of the pyramid, were found to have a significant amount of capping character. The metal-metal bonding orbitals have some unusual features due to the pyramid's distortion. Additionally, the flattened nature of the pyramid leads to an interesting energy ordering of the metal-metal bonding orbitals.     

Reactivity and infrared spectroscopy of gaseous hydrated trivalent metal ions

Hydrated trivalent rare earth metal ions containing yttrium and all naturally abundant lanthanide metals are formed using electrospray ionization, and the structures and reactivities of these ions containing 17-21 water molecules are probed using blackbody infrared radiative dissociation (BIRD) and infrared action spectroscopy. With the low-energy activation conditions of BIRD, there is an abrupt transition in the dissociation pathway from the exclusive loss of a single neutral water molecule to the exclusive loss of a small protonated water cluster via a charge-separation process. This transition occurs over a narrow range of cluster sizes that differs by only a few water molecules for each metal ion. The effective turnover size at which these two dissociation rates become equal depends on metal ion identity and is poorly correlated with the third ionization energies of the isolated metals but is well correlated with the hydrolysis constants of the trivalent metal ions in bulk aqueous solution. Infrared action spectra of these ions at cluster sizes near the turnover size are largely independent of the specific identity of the trivalent metal ion, suggesting that any differences in the structures of the ions present in our experiment are subtle.     

过渡金属簇合物合成化学

本文以与催化作用紧密相关的金属羰基簇合物的合成和与化学仿生相关的铁硫和钼铁硫簇合物的合成为例,评述了过渡金属簇合物合成化学的发展概况,给出了金属-金属间键合的两条通则(低氧化态金属间容易成键和同一族元素中重金属具有较大的成键倾向)和三类簇合物的主要合成路线。     

Bonding between strongly repulsive metal atoms: an oxymoron made real in a confined space of endohedral metallofullerenes

Endohedral metallofullerenes (EMFs) are able to encapsulate up to four metal atoms. In EMFs, metal atoms are positively charged because of the electron transfer from the endohedral metal atoms to the carbon cage. It results in the strong Coulomb repulsion between the positively charged ions trapped in the confined inner space of the fullerene. At the same time, in many EMFs, such as Lu(2)@C(76), Y(2)@C(79)N, M(2)@C(82) (M = Sc, Y, Lu, etc.), Y(3)@C(80), or Sc(4)O(2)@C(80), metals do not adopt their highest oxidation states, thus yielding a possibility of the covalent metal-metal bonding. In some other EMFs (e.g., La(2)@C(80)), metal-metal bonding evolves as the result of the electrochemical or chemical reduction, which leads to the population of the metal-based LUMO with pronounced metal-metal bonding character. This article highlights different aspects of the metal-metal bonding in EMFs. It is concluded that the valence state of the metal atoms in dimetallofullerenes is not dependent on their third ionization potential, but is determined by their ns(2)(n- 1)d(1)→ns(1)(n- 1)d(2) excitation energies. Peculiarities of the metal-metal bonding in EMFs are described in terms of molecular orbital analysis as well as topological approaches such as Quantum Theory of Atoms in Molecules and Electron Localization Function. Interplay of Coulomb repulsion and covalent bonding is analyzed in the framework of the Interacting Quantum Atom approach.     

过渡金属络合物成键本质分析的常用方法

过渡金属络合物中过渡金属与配体间所形成的化学键的成键本质,可以在理论化学基础上,采用定量的方法进行分析。本文重点以铁羰基络合物为例,对常用的分析方法,如自然键轨道方法(NBO)、电荷分解分析(CDA)、分子中的原子(AIM)拓扑分析方法以及ETS和EDA能量分解方法等,在应用中的优缺点进行了分析和评述。借助于这些方法提供的电荷、能量和电子密度等配分项可以深刻认识和理解过渡金属-配体间形成的化学键的成键本质。     

The dimensionality and topology of chemical bonding manifolds in metal clusters and related compounds

The chemical bonding manifolds in metal cluster skeletons (as well as in skeletons of clusters of other elements such as boron or carbon) may be classified according to their dimensionalities and their chemical homeomorphism to various geometric structures. The skeletal bonding manifolds of discrete metal cluster polyhedra may be either one-dimensional edge-localized or three-dimensional globally delocalized, although two-dimensional face-localized skeletal bonding manifolds are possible in a few cases. Electron precise globally delocalized metal cluster polyhedra withv vertices have 2v + 2 skeletal electrons and form deltahedra with no tetrahedral chambers having total skeletal bonding manifolds chemically homeomorphic to a closed ball. Electron-rich metal cluster polyhedra withv vertices have more than 2v + 2 skeletal electrons and form polyhedra with one or more non-triangular faces, whereas electron-poor metal cluster polyhedra withv vertices have less than 2v + 2 skeletal electrons and form deltahedra with one or more tetrahedral chambers. Fusion of metal cluster octahedra by sharing (triangular) faces forms three-dimensional analogues of polycyclic aromatic hydrocarbons such as naphthalene, anthracene, and perinaphthenide. Fusion of metal cluster octahedra by sharing edges can be extended infinitely into one and two dimensions forming chains (e.g. Gd₂Cl₃) and sheets (e.g. ZrCl), respectively. Infinite extension of such fusion of metal cluster octahedra into all three dimensions leads to bulk metal structures. Unusual anionic platinum carbonyl clusters can be contructed from stacks of Pt₃ triangles or Pt₅ pentagons. The resulting platinum polyhedra appear to exhibit edge-localized bonding, supplemented by unusual types of delocalized bonding at the top and the bottom of the stacks. Superconducting ternary molybdenum chalcogenides and lanthanide rhodium borides consist of infinite lattices of electronically linked edge-localized Mo₆ octahedra or Rh₄ tetrahedra, leading naturally to the idea of porous delocalization in superconducting materials.     

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。     

无机-有机复合聚合物:材料研究的一个新领域

无机-有机复合聚合物特别是类分子筛聚合物、类多层钙钛矿和仿生物材料的合成及其应用研究成为近几年来一个热门的研究领域。我们瞄准了这一前沿领域并合成和表征了以下四个系列具有纳米孔洞的分子笼和一维、二维或三维的新型无机聚合物:(1)带有纳米尺寸空腔和孔状结构的新型过渡金属和稀土金属聚合物;(2)含有螺旋链的一维链状聚合物;(3)具有石墨形态层状结构和优异导电性能的聚合物;(4)以强金属-金属相互作用为核心、有机分子为稳定外壳的纳米线聚合物。本文总结这四个系列化合物的合成结构和特性。     

Protein-Inspired Polymers with Metal-Site-Regulated Ordered Conformations

Metal ions play critical roles in facilitating peptide folding and inducing conformational transitions, thereby impacting on the biological activity of many proteins. However, the effect of metal sites on the hierarchical structures of biopolymers is still poorly understood. Herein, inspired by metalloproteins, we report an order-to-order conformational regulation in synthetic polymers mediated by a variety of metal ions. The copolymers are decorated with clinically available desferrioxamine (DFO) as an exogenous ligand template, which presents a geometric constraint toward peptide backbone via short-range hydrogen bonding interactions, thus dramatically altering the secondary conformations and self-assembly behaviors of polypeptides and allowing for a controllable β-sheet to α-helix transition modulated by metal–ligand interactions. These metallopolymers could form ferritin-inspired hierarchical structures with high stability and membrane activity for efficient brain delivery across the blood–brain barrier (BBB) and long-lasting magnetic resonance imaging (MRI) in vivo.     

Mononuclear versus binuclear metal-binding sites: metal-binding affinity and selectivity from PDB survey and DFT/CDM calculations

Binuclear metal centers in metalloenzymes are involved in a number of hydrolytic, hydration, isomerization, and redox processes. Despite the growing number of studies elucidating their structure, properties, and function, questions regarding certain aspects of the bimetallic proteins' biochemistry still remain, e.g., the following: (i) What are the general characteristics of binuclear sites found in 3D structures such as the range of metal-metal distances and the most common ligand bridging the two metal cations? (ii) How does the presence of a metal cation in one of the binuclear sites affect the metal-binding affinity/selectivity of the other site? (iii) How do the characteristics and metal-binding affinity/selectivity of binuclear sites compare with those of their mononuclear counterparts? Here we address these questions by combining a Protein Data Bank survey of binuclear sites with density functional theory (DFT) combined with continuum dielectric method (CDM) calculations. The results reveal that, for homobinuclear sites, the metal separation depends on the metal's charge and electron-accepting ability, and Asp-/Glu-, bidentately bound to the two cations, is the most common bridging ligand. They also reveal that Mg2+ occupying one of the binuclear sites attenuates the metal-binding affinity but enhances the selectivity of its neighboring site, compared to the corresponding mononuclear counterparts. These findings are consistent with available experimental data. The weak metal binding of one of the binuclear sites would enhance the metal cofactor mobility in achieving the transition state, whereas the enhanced selectivity of Mg2+-Mg2+ centers helps protect against unwanted substitutions by transition metal ions, which are generally stronger Lewis acids compared to Mg2+.     

Cluster ion structures formed by positive and negative chemical ionization of lactic and other hydroxyacids

Both positive ion and negative ion chemical ionization mass spectra of hydroxycarboxylic acids (hydroxyethanoic acid, 3-hydroxypropanic acid, 2-hydroxypropanoic acid and 1-phenyl-1-hydroxyethanoic acid) show intense oligomeric ions when the samples are evaporated into a chemical ionization source. The observation of oligomeric anionic and cationic species is unusual, and the parallel behavior observed between the positive and negative ion mass spectra is striking. These results are explicable in terms of evaporation of oligomers and their dehydration products from the hot probe, although gas phase clustering reactions of singly charged ions are not excluded. Hydrogen bonding and dehydration provide bonding within each cluster. The structures of the ions have been confirmed by recording the collision induced dissociations of individual cluster ions via their mass analyzed ion kinetic energy spectra. Temperature dependence of the chemical ionization mass spectra provides a method for distinguishing hydrogen bonding from covalent bonding and gives further structural information on the cluster ions.     

Electronic structures of M21S8 (M = Nb, Zr) and (M,M')21S8 (M, M' = Hf, Ti; Nb, Ta) phases and reasons for variations in the metal site occupations

The electronic structures of binary M21S8 (M = Nb, Zr) and isostructural ternary (M,M')21S8 (M, M' = Hf, Ti; Nb, Ta) phases have been studied by means of extended Hückel tight-binding band structure calculations. For the valence electron concentration in the binary group 5 metal phase Nb21S8, metal-metal bonding is optimized whereas, in the isostructural group 4 metal phase Zr21S8, metal-metal bonding levels exist above the Fermi level. However, the electronic structure analysis suggests a stable structure for M21S8 phases with group 4 metals and that (M,M')21S8 phases with mixed group 4 and group 5 metals, even if not yet reported, could well exist. In the ternary phase Nb6.9Ta14.1S8, a linear relationship exists between the magnitude of the metal-metal bonding capacity (as expressed by the total metal-metal Mulliken overlap population) of each crystallographically independent metal site and the occupation of the site with the heavier metal (i.e., the element with the greater bonding capability). The situation is quite more complex in Hf7.5Ti13.5S8, where the metal-metal bonding capacity of each site, differences in electronegativity between Ti and Hf, and site volume arguments must be taken into account to understand the metal site occupation.     

New spin-transition-like copper(II)-nitroxide species

Novel copper(II)-nitroxide complexes exhibiting a spin-transition-like behavior have been prepared and characterized. They include meso, chiral, and racemic 2-(3-pyridyl)-nitronyl nitroxides differently substituted in positions 4 and/or 5 by ethyl groups and pyrimidyl nitroxides. Depending on the stoichiometry of the reaction, tetranuclear and binuclear complexes were obtained whose structures are cyclic. The tetranuclear species, which include two intracyclic and two exocyclic metal sites, are similar to the previously reported complex of the tetramethylated analogue, while the binuclear complexes involve only endocyclic metal ions and have uncoordinated N-oxyl groups. The tetranuclear complexes exist as two isomers depending on the temperature of crystallization: at room temperature, N-oxyl ligand coordination is axial-axial, while it is axial-equatorial at low temperature. Unexpectedly, this isomerism concerns N-oxyl bonding to the exocyclic metal centers for the derivatives of 4,5-diethyl-substituted ligands while it involves the endocyclic metal site in the complex of the monoethylated ligand, which converts reversibly from a high-spin state to a low-spin state, as observed for the complex of the tetramethylated ligand. Binuclear complexes are diamagnetic at room temperature but convert to a paramagnetic state on warming (90-110 degrees C); the transition is irreversible and sharp.