A stable silicon(0) compound with a Si=Si double bond

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.     

Atomlike, hollow-core-bound molecular orbitals of C60

The atomic electron orbitals that underlie molecular bonding originate from the central Coulomb potential of the atomic core. We used scanning tunneling microscopy and density functional theory to explore the relation between the nearly spherical shape and unoccupied electronic structure of buckminsterfullerene (C60) molecules adsorbed on copper surfaces. Besides the known pi* antibonding molecular orbitals of the carbon-atom framework, above 3.5 electron volts we found atomlike orbitals bound to the core of the hollow C60 cage. These "superatom" states hybridize like the s and p orbitals of hydrogen and alkali atoms into diatomic molecule-like dimers and free-electron bands of one-dimensional wires and two-dimensional quantum wells in C60 aggregates. We attribute the superatom states to the central potential binding an electron to its screening charge, a property expected for hollow-shell molecules derived from layered materials.     

双原子分子物质混合物界面吸附的维里展开

讨论双原子分子物质混合物界面的吸附量,得到二维空间展开的维里系数,可看出,二维展开是三维护展开的特例。     

Complex patterning by vertical interchange atom manipulation using atomic force microscopy

The ability to incorporate individual atoms in a surface following predetermined arrangements may bring future atom-based technological enterprises closer to reality. Here, we report the assembling of complex atomic patterns at room temperature by the vertical interchange of atoms between the tip apex of an atomic force microscope and a semiconductor surface. At variance with previous methods, these manipulations were produced by exploring the repulsive part of the short-range chemical interaction between the closest tip-surface atoms. By using first-principles calculations, we clarified the basic mechanisms behind the vertical interchange of atoms, characterizing the key atomistic processes involved and estimating the magnitude of the energy barriers between the relevant atomic configurations that leads to these manipulations.     

Silacalix-

The synthesis of polyphosphinine macrocycles, which consist of a 16-membered ring with four phosphorus atoms (P4) and a 12-membered ring with three phosphorus atoms (P3), is described. Their high coordination ability is demonstrated by the quantitative synthesis of the rhodium and iridium cation complexes of the P4 macrocycle and by quantitative synthesis of the W(CO)3 complex of the P3 compound. Unlike the other available macrocyclic ligands bearing oxygen, sulfur, di- or tricoordinate nitrogen, and even tricoordinate phosphorus as ligating atoms, which are all essentially final sigma donors, these dicoordinate phosphorus-based macrocycles have strong pi-acceptor properties. Their use can be envisaged for the stabilization of negative oxidation states of transition metals or in reductive catalysis.     

Oxidative addition of ammonia to form a stable monomeric amido hydride complex

The insertion of an iridium complex into an N-H bond in ammonia leads to a stable monomeric amido hydride complex in solution at room temperature. This reaction advances the transition-metal coordination chemistry of ammonia beyond its role for more than a century as an ancillary ligand. The precursor for this insertion reaction is an iridium(I) olefin complex with an aliphatic ligand containing one carbon and two phosphorus donor atoms. Kinetic and isotopic labeling studies indicate that olefin dissociates to give a 14-electron iridium(I) fragment, which then reacts with ammonia. This cleavage of the N-H bond under neutral conditions provides a foundation on which to develop future mild catalytic transformations of ammonia, such as olefin hydroamination and arene oxidative amination.     

苯甲酰丙酮反应位点预测及金属配合物的合成、表征和抑菌活性

运用Gaussian98软件包,采用密度泛函方法,在B3LYP/6-31G基组水平上,对苯甲酰丙酮进行了结构优化、频率分析和NBO轨道分析。结合前线分子轨道能量和原子净电荷等,推导出化合物可能的活性部位是β-二酮的氧原子。利用频率分析的结果对样品的红外光谱图进行了指认。合成并表征了苯甲酰丙酮的铜、锌配合物,确定了金属配合物的可能配位点,结果与量化计算的结果一致。采用单片纸碟法测定了配合物的抑菌活性,结果表明,苯甲酰丙酮的铜配合物抑菌活性好于对照物阿莫西林。     

Rotational coherence and a sudden breakdown in linear response seen in room-temperature liquids

Highly energized molecules normally are rapidly equilibrated by a solvent; this finding is central to the conventional (linear-response) view of how chemical reactions occur in solution. However, when a reaction initiated by 33-femtosecond deep ultraviolet laser pulses is used to eject highly rotationally excited diatomic molecules into alcohols and water, rotational coherence persists for many rotational periods despite the solvent. Molecular dynamics simulations trace this slow development of molecular-scale friction to a clearly identifiable molecular event: an abrupt liquid-structure change triggered by the rapid rotation. This example shows that molecular relaxation can sometimes switch from linear to nonlinear response.     

Condensed-matter energetics from diatomic molecular spectra

Analyses of molecular spectra and compression data from crystals show that a single function successfully describes the dependence on interatomic separation of both the potential energy of diatomic molecules and the cohesive binding energy of condensed matter. The empirical finding that one function describes interatomic energies for such diverse forms of matter and over a wide range of conditions can be used to extend condensed-matter equations of state but warrants further theoretical study.     

Structure of the polycrystalline zeolite catalyst IM-5 solved by enhanced charge flipping

Despite substantial advances in crystal structure determination methodology for polycrystalline materials, some problems have remained intractable. A case in point is the zeolite catalyst IM-5, whose structure has eluded determination for almost 10 years. Here we present a charge-flipping structure-solution algorithm, extended to facilitate the combined use of powder diffraction and electron microscopy data. With this algorithm, we have elucidated the complex structure of IM-5, with 24 topologically distinct silicon atoms and an unusual two-dimensional medium-pore channel system. This powerful approach to structure solution can be applied without modification to any type of polycrystalline material (e.g., catalysts, ceramics, pharmaceuticals, complex metal alloys) and is therefore pertinent to a diverse range of scientific disciplines.     

Synthesis and structure determination of the hierarchical meso-microporous zeolite ITQ-43

The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography.     

Direct imaging of transient molecular structures with ultrafast diffraction

Ultrafast electron diffraction (UED) has been developed to study transient structures in complex chemical reactions initiated with femtosecond laser pulses. This direct imaging of reactions was achieved using our third-generation apparatus equipped with an electron pulse (1.07 +/- 0.27 picoseconds) source, a charge-coupled device camera, and a mass spectrometer. Two prototypical gas-phase reactions were studied: the nonconcerted elimination reaction of a haloethane, wherein the structure of the intermediate was determined, and the ring opening of a cyclic hydrocarbon containing no heavy atoms. These results demonstrate the vastly improved sensitivity, resolution, and versatility of UED for studying ultrafast structural dynamics in complex molecular systems.     

In Situ X-ray Absorption Study of Surface Complexes: Selenium Oxyanions on agr-FeOOH

A novel application of x-ray absorption spectroscopy has provided structural information for ions sorbed at oxide-water interfaces. As an example, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at ah alpha-FeOOH(goethite)-water interface have been performed; these measurements show that selenate forms a weakly bonded, outer-sphere complex and that selenite forms a strongly bonded, inner-sphere complex. The selenite ion is bonded directly to the goethite surface in a bidentate fashion with two iron atoms 3.38 angstroms from the selenium atom. Adsorbed selenate has no iron atom in the second coordination shell of selenium, which indicates retention of its hydration sphere upon sorption. This method provides direct structural information for adsorbed species at solid-liquid interfaces.     

Ultrafast probing of core hole localization in N2

Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether the core vacancy created in a homonuclear diatomic molecule by absorption of a single x-ray photon is localized on one atom or delocalized over both. We have been able to clarify this question with an experiment that uses Auger electron angular emission patterns from molecular nitrogen after inner-shell ionization as an ultrafast probe of hole localization. The experiment, along with the accompanying theory, shows that observation of symmetry breaking (localization) or preservation (delocalization) depends on how the quantum entangled Bell state created by Auger decay is detected by the measurement.     

Photofragment helicity caused by matter-wave interference from multiple dissociative states

Isolated diatomic molecules of iodine monochloride (ICl) were photodissociated by a beam of linearly polarized light, and the resulting ground-state Cl atom photofragments were detected by a method that is sensitive to the handedness (helicity) of the electronic angular momentum. It was found that this helicity oscillates between "topspin" and "backspin" as a function of the wavelength of the dissociating light. The helicity originates solely from the (de Broglie) matter-wave interference of multiple dissociating pathways of the electronic excited states of ICl. These measurements can be related to the identity and to the detailed shapes of the dissociating pathways, thus demonstrating that it is possible to probe repulsive states by spectroscopic means.     

Single-crystal-like diffraction data from polycrystalline materials

A method for solving structures from powder diffraction data was developed, and its validity was demonstrated on three complex structures. The method uses a textured sample and exploits the high intensity and parallel nature of synchrotron radiation. In principle, crystal structures as complex as those routinely solved by single-crystal methods can be determined with this approach. For example, the as-synthesized form of the zeolite UTD-1, with 69 nonhydrogen atoms in the asymmetric unit, could be solved directly. With this method, a larger range of structural complexity becomes accessible to scientists interested in the structures of polycrystalline materials that cannot be grown as single crystals.     

丁香酸金属铜配合物的合成·表征及其抗内毒素作用研究

[目的]合成丁香酸金属铜配合物,比较丁香酸及其配合物的抗内毒素活性。[方法]在无水乙醇溶液中制备了丁香酸（H2SA）与铜（Cu2＋）的金属配合物,并通过紫外（UV）、红外（IR）和元素分析对配合物进行了表征,同时采用鲎试验法定量测定并比较二者对内毒素的破坏率。[结果]丁香酸金属铜配合物的组成为（C9H8O5）Cu·H2O。1.25mg/ml丁香酸水溶液对内毒素的破坏率为83.03%,而同浓度的丁香酸铜配合物水溶液的破坏率为86.60%。[结论]铜离子同时与丁香酸中羧基和羟基的氧原子配位,形成1∶1型的配合物,其抗内毒素活性较配体有所增强。     

N₂reduction and hydrogenation to ammonia by a molecular iron-potassium complex

The most common catalyst in the Haber-Bosch process for the hydrogenation of dinitrogen (N(2)) to ammonia (NH(3)) is an iron surface promoted with potassium cations (K(+)), but soluble iron complexes have neither reduced the N-N bond of N(2) to nitride (N(3-)) nor produced large amounts of NH(3) from N(2). We report a molecular iron complex that reacts with N(2) and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations. The product has a Fe(3)N(2) core, implying that three iron atoms cooperate to break the N-N triple bond through a six-electron reduction. The nitride complex reacts with acid and with H(2) to give substantial yields of N(2)-derived ammonia. These reactions, although not yet catalytic, give structural and spectroscopic insight into N(2) cleavage and N-H bond-forming reactions of iron.     

Shattuckite and plancheite: a crystal chemical study

The orthorhombic crystal structures of shattuckite, Cu(5)( SiO(3))(4)(OH)(2) and planchétite, Cu(8)(Si(4)0(11))(2)(OH)(4) H(2)O, have been solved. Shattuckite contains silicate chains similar to pyroxene in a complex association with copper atoms, while the closely related planchéite contains silicate chains similar to amphibole.     

Ion binding by synthetic macrocyclic compounds

The existence of synthetic macrocyclic molecules with hydrophilic cavities containing multiple binding atoms and with hydrophobic exteriors gives rise to extraordinary possibilities with respect to the design and synthesis of molecules with specific cation and anion binding properties. The preparation of many new macrocyclic compounds has recently been reported, but few practical applications for them have been suggested. From the information available, it is becoming clear that it should be possible to synthesize macrocycles that will have specified, or selected, ion binding properties. Cavity size can be varied to accommodate only those cations or anions within a specified narrow band of sizes. Numbers and types of coordinating atoms can be chosen to give essentially electrostatic or covalent bonding or a combination of the two in a metalmacrocycle complex. The metal ligand bond appears to be predominantly ionic in the case of the cyclic polyethers but the covalent character increases on substitution of sulfur or nitrogen for oxygen donor atoms. The essential hydrophobic exteriors of the macrocycles can be modified by the addition of side chains and groups to facilitate the solution of anions and cations in organic solvents. The structures of many macrocycles can be made to approximate naturally occurring molecules, that is, cyclic polyethers similar to macrocyclic antibiotics of the valinomycin and nonactin types and cyclic polyamines similar to porphyrins. Macrocycles are also useful as model compounds for the study of metal interactions with biological systems. The synthetic macrocycles thus represent an intriguing new area of coordination chemistry, the systematic study of which should lead to many interesting and useful chemical applications in the field of metal complexation in solution.