Organic molecular soft ferromagnetism in a fullerene c60

The properties of an organic molecular ferromagnet [C(60)TDAE(0.86); TDAE is tetrakis(dimethylamino)ethylene] with a Curie temperature ;T(c) = 16.1 kelvin are described. The ferromagnetic state shows no remanence, and the temperature dependence of the magnetization below ;T(c) does not follow the behavior expected of a conventional ferromagnet. These results are interpreted as a reflection of a three-dimensional system leading to a soft ferromagnet.     

Taming superacids: stabilization of the fullerene cations HC60+ and C60.+

A new superacid, H(CB11H6X6) (where X = chlorine or bromine), whose conjugate base is the exceptionally inert CB11H6X6- carborane anion, separates Bronsted acidity from oxidizing capacity and anion nucleophilicity in a manner not previously achieved. Reaction of this superacid with C60 gives HC60+ as a stable ion in solution and in the solid state. In a separate experiment, an oxidant was developed such that the long-sought C60.+ ion can be synthesized in solution. The preparation of these two fullerene carbocations is a notable departure from the prevalent chemistry of C60, which is dominated by the formation of anions or the addition of nucleophiles. The H(CB11H6X6) superacid overcomes the major limitations of presently known superacids and has potentially wide application.     

A rational chemical synthesis of C60

Isolable quantities of C60, the smallest stable fullerene, have been synthesized in 12 steps from commercially available starting materials by rational chemical methods. A molecular polycyclic aromatic precursor bearing chlorine substituents at key positions forms C60 when subjected to flash vacuum pyrolysis at 1100 degrees C. No other fullerenes are formed as by-products. The methods we have developed for the target-specific synthesis of fullerenes, applied here to a synthesis of C60, should make possible the directed laboratory preparation of other fullerenes as well, including those not accessible by graphite vaporization.     

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.     

Visualization of the molecular Jahn-Teller effect in an insulating K4C60 monolayer

We present a low-temperature scanning tunneling microscopy (STM) study of K(x)C60 monolayers on Au(111) for 3 < or = x < or = 4. The STM spectrum evolves from one that is characteristic of a metal at x = 3 to one that is characteristic of an insulator at x = 4. This electronic transition is accompanied by a dramatic structural rearrangement of the C60 molecules. The Jahn-Teller effect, a charge-induced mechanical deformation of molecular structure, is directly visualized in the K4C60 monolayer at the single-molecule level. These results, along with theoretical analyses, provide strong evidence that the transition from metal to insulator in K(x)C60 monolayers is caused by the Jahn-Teller effect.     

Photoproduction of molecular hydrogen by a plant-algal symbiotic system

The rapidly growing water fern Azolla, which contains a nitrogen-fixing blue-green algal symbiont, has been studied as a possible system for photoproduction of molecular hydrogen. When this plant is grown on a combined nitrogen supply, photochemically generated hydrogen can be diverted through the algal nitrogenase system, which serves as a source of molecular hydrogen generated from water. This symbiosis has several advantages as a possible biological energy conversion system.     

Selenium in organic synthesis

The introduction, manipulation, and ultimate removal of selenium-containing functional groups allow a variety of synthetically useful processes to be accomplished in high overall yields under mild conditions. In particular, transformations such as allylic oxidations, nucleophile-induced cleavage reactions, regiospecific alkylations, and olefin cofunctionalizations can be readily achieved by taking advantage of selenium's unique properties.     

Orientational Disorder of C60 in Li2CsC60

The x-ray diffraction of the nonsuperconducting ternary fulleride Li(2)CsC(60) reveals at room temperature a face-centered-cubic (Fm3m) disordered structure that persists to a temperature of 13 Kelvin. The crystal structure is best modeled as containing quasispherical [radius of 3.556(4) angstroms] C(60)(3-) ions, in sharp contrast to their orientational state in superconducting face-centered-cubic K(3)C(60) (merohedral disorder) and primitive cubic Na(2)CsC(60) (orientational order). The orientational disorder of the carbon atoms on the C(60)(3-) sphere was analyzed with symmetry-adapted spherical-harmonic functions. Excess atomic density is evident in the <111> directions, indicating strong bonding Li(+)-C interactions, not encountered before in any of the superconducting alkali fullerides. The intercalate-carbon interactions and the orientational state of the fullerenes have evidently affected the superconducting pair-binding mechanism in this material.     

Computer-assisted analysis in organic synthesis

The planning of alternative routes for the synthesis of complex organic molecules has been facilitated by the formulation of guiding strategies that can be applied to a broad range of problems. Analysis of organic synthesis can be carried out in the retrosynthetic direction, opposite to the actual process of chemical synthesis, or bidirectionally, that is, as a combined retrosynthetic and synthetic search. An interactive computer program is described which utilizes the general strategies of retrosynthetic analysis and an appropriate database to generate pathways of chemical intermediates for chemical synthesis of a particular target structure. Computer graphics and standard chemical structures are used for man-machine communication.     

Enzymatic catalysts in organic synthesis

The synthetic value of enzymes is being increasingly recognized. With an understanding of enzyme-catalyzed reactions and the techniques now available for the low-cost production and rational alteration of enzymes and for the design of new enzymatic activities, biocatalytic synthesis should become one of the most valuable synthetic methods. The fundamental as well as the practical issues of this rapidly growing area are described and its impact on the technology pertaining to synthesis is considered.     

C60H2: Synthesis of the Simplest C60 Hydrocarbon Derivative

The reaction of C(60) with BH(3): tetrahydrofuran in toluene followed by hydrolysis yielded C(60)H(2). This product was separated by high-performance liquid chromatography and characterized as the addition product of H(2) to a 6,6-ring fusion (1alb isomer). The (1)H nuclear magnetic resonance (NMR) spectrum of the product remained a sharp singlet between -80 degrees and +100 degrees C, which suggests a static structure on the NMR time scale. Hydrolysis of the proposed borane addition product with acetic acid-d(1) or D(2)O yielded C(60)HD, and its (3)J(HD) coupling constant is consistent with vicinal addition. The observation of a single C(60)H(2) isomer is in complete agreement with earlier calculations that indicated that at most 2 of the 23 possible isomers of C(60) would be observable at equilibrium at room temperature. These results suggest that organoborane chemistry may be applied to further functionalization of fullerenes.     

High-temperature superconductivity in lattice-expanded C60

C60 single crystals have been intercalated with CHCl3 and CHBr3 in order to expand the lattice. High densities of electrons and holes have been induced by gate doping in a field-effect transistor geometry. At low temperatures, the material turns superconducting with a maximum transition temperature of 117 K in hole-doped C60/CHBr3. The increasing spacing between the C60 molecules follows the general trend of alkali metal-doped C60 and suggests routes to even higher transition temperatures.     

低分子量有机酸及其共聚物去除土壤重金属研究

为探究低分子有机酸以及其共聚物对土壤中重金属的去除效果,通过振荡淋洗法研究了富马酸和丙烯酸-2-丙烯酰胺基-2-甲基丙磺酸共聚物在不同浓度、pH和时间条件下对土壤中Cd、Pb和Zn的去除率,并采用传统人工螯合剂乙二胺四乙酸做对比。结果表明,土壤中Cd、Pb和Zn的去除率随着有机酸浓度的增加呈现先上升后趋于平稳的趋势。丙烯酸-2-丙烯酰胺基-2-甲基丙磺酸共聚物和富马酸在浓度为10 g·L-1时对Cd、Pb和Zn的去除率分别为54.75%、69.60%、51.42%和42.03%、55.00%、46.97%,乙二胺四乙酸对Cd和Pb的去除率与富马酸趋于一致,但其对Zn的去除率显著低于富马酸(P0.05),仅为34.11%。两种有机酸对重金属去除率受pH的影响较大,其在pH为4~5时能有效去除土壤中Cd、Pb和Zn;富马酸在60 min时达到最大去除率,而丙烯酸-2-丙烯酰胺基-2-甲基丙磺酸共聚物在大于120 min时去除率最高。此外,经过两种有机酸和人工螯合剂乙二胺四乙酸淋洗后,土壤中Cd、Pb和Zn的可交换态和碳酸盐结合态含量大幅度下降。因此,富马酸和丙烯酸-2-丙烯酰胺基-2-甲基丙磺酸共聚物对重金属污染土壤具有潜在修复能力。     

Packing C60 in boron nitride nanotubes

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.     

C-H bond functionalization in complex organic synthesis

Direct and selective replacement of carbon-hydrogen bonds with new bonds (such as C-C, C-O, and C-N) represents an important and long-standing goal in chemistry. These transformations have broad potential in synthesis because C-H bonds are ubiquitous in organic substances. At the same time, achieving selectivity among many different C-H bonds remains a challenge. Here, we focus on the functionalization of C-H bonds in complex organic substrates catalyzed by transition metal catalysts. We outline the key concepts and approaches aimed at achieving selectivity in complex settings and discuss the impact these reactions have on synthetic planning and strategy in organic synthesis.     

Free-radical carbon-carbon bond formation in organic synthesis

Organic chemists have begun to use intra- and intermolecular free-radical addition reactions to develop useful synthetic transformations. Carboncentered radicals can form bonds with electron-rich or electron-deficient alkenes, allenes, and acetylenes. Radical addition reactions can also be used to construct hindered carbon-carbon bonds. These characteristics, as well as the large number of functional groups that tolerate free-radical conditions contribute to the importance of such reactions in organic synthesis.     

Fractional quantum hall effect in organic molecular semiconductors

High-quality crystals of the organic molecular semiconductors tetracene and pentacene were used to prepare metal-insulator-semiconductor (MIS) structures exhibiting hole and electron mobilities exceeding 10(4) square centimeters per volt per second. The carrier concentration in the channel region of these ambipolar field-effect devices was controlled by the applied gate voltage. Well-defined Shubnikov-de Haas oscillations and quantized Hall plateaus were observed for two-dimensional carrier densities in the range of 10(11) per square centimeter. Fractional quantum Hall states were observed in tetracene crystals at temperatures as high as approximately 2 kelvin.     

Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C60 Derivative, C60Br24

C(60) and liquid bromine react to form C(60)Br(24), a crystalline compound isolated as a bromine solvate, C(60)Br(24)(Br(2))(x), The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C(60) framework is recognizable in C(60)Br(24), but sp(3) carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 degrees to 200 degrees C there is effectively quantitative reversion of C(60)Br(24) to C(60) and Br(2).     

C60分子中原子坐标的计算

运用Ｃ６０分子的Ｉｎ对称性及矢量运算方法，引入调节参数λ计算了正二十面体被截取顶角后的具有Ｃ６０分子结构的原子坐标，当输入的调节参数λ＝０．３３７，Ｃ６０分子的半径Ｒｃ＝３．５５Ａ时，计算得到的长短键分别为１．４４９６Ａ和１．４０Ａ，与测量值相符，并计算了在Ｃ６０面心立方晶体为１．４４９６Ａ和１．４０Ａ，与实验测量值相符，并计算了在Ｃ６０面心立方晶体中，Ｃ６０的二次轴与晶轴取向一致时的各碳原子坐标