镁基储氢合金的表面处理和表面催化

表面处理作为储氢合金性能改善的有效手段，近年来得到了很好的发展和应用，本文简要介绍了镁基储氢合金表面处理的主要方法及其对合金性能的影响。     

Resolution limitations from detector pulse width and jitter in a linear orthogonal-acceleration time-of-flight mass spectrometer

Recent and ongoing advances in timing electronics together with the development of ionization techniques suited to time-of-flight mass spectrometry (TOF-MS) have contributed to renewed interest in this method of mass analysis. Whereas low resolving powers (m/?m < 500) were once an almost unavoidable drawback in TOF-MS, recent developments in instrument geometries have produced much higher resolving powers for many ion sources. The temporal width of detector pulses and jitter in timing electronics, however, lead to contributions to peak widths that are essentially independent of the mass-analyzer ion optics. The effective detector pulse width (?t _d ≈ 1–10 ns typically) can be a limiting factor in the development of high resolution time-of-flight (TOF) instruments with modest drift lengths (～1 m), It also reduces the mass resolution more seriously for light ions. This article presents a method for distinguishing the instrumental “ion arrival-time” resolution (R _o) of a linear TOF mass analyzer from that which is locally measured at a particular mass, limited by the broadening of the detector pulse width and electronics. The method also provides an estimate of ?t _d, that is useful in determining the temporal performance of the detection system. The model developed here is tested with data from a recently constructed orthogonal-acceleration TOF mass spectrometer equipped with a commercially available transient recorder (a LeCroy 400-Msamplejs digital oscilloscope) from which we obtained R _o = 4240 ± 100 [full width at half maximum (FWHM)) and ?t _d = 3.0 ± 0.1 ns (FWHM).     

Statistical theory for hydrogen bonding fluid system of A_aD_d type (I): The geometrical phase transition

The influence of hydrogen bonds on the physical and chemical properties of hydrogen bonding fluid system of AaDd type is investigated from two viewpoints by the principle of statistical mechanics. In detail, we proposed two new ways that can be used to obtain the equilibrium size distribution of the hydrogen bonding clusters, and derived the analytical expression of a relationship between the hydrogen bonding free energy and hydrogen bonding degree. For the nonlinear hydrogen bonding systems, it is shown that the sol-gel phase transition can take place under proper conditions, which is further proven to be a kind of geometrical phase transition rather than a thermodynamic one. Moreover, several problems associated with the geometrical phase transition and liquid-solid phase transition in nonlinear hydrogen bonding systems are discussed.     

A conformational study of phospha(III)- and phospha(V)-guanidine compounds

Spectroscopic, crystallographic, and computational studies of the substituent distribution about the "NCN" unit in a series of phospha(III)- and phospha(V)-guanidines, R(2)PC{NR'}{NHR'} and R(2)P(E)C{NR'}{NHR'} (R = Ph, Cy; R' = (i)Pr, Cy; E = S, Se), are reported. In the phosphorus(III) systems, the P-diphenyl substituted compounds are observed as only one isomer, shown by NMR spectroscopy to be the E(syn)-(alpha) configuration. In contrast, the corresponding P-dicyclohexyl derivatives exist as a mixture of E(syn)-(alpha) and Z(anti) in solution. Spectroscopic techniques are unable to determine whether the latter isomer exists as the alpha- or beta-conformer relative to rotation about the P-C(amidine)() bond; however, DFT calculations indicate a low-energy structure for the N,N'-dimethyl model complex in the beta-conformation. In their oxidized sulfo and seleno forms, the P-diphenyl compounds are present as an interconverting equilibrium mixture of the E(syn)-(beta) and Z(syn)-(beta) isomers in solution ( approximately 3:2 ratio), whereas for the P-dicyclohexyl analogues, the latter configuration (in which the nitrogen substituents are in a more sterically unfavorably cisoid arrangement about the imine double bond) is the dominant form. Intramolecular E...HN (E = S, Se) interactions are observed in solution for the Z(syn)-(beta) configuration of both P-substituted species, characterized by J(SeH) coupling in the NMR spectrum for the P(V)-seleno compounds and a bathochromic shift of the NH absorption in the infrared spectrum. An X-ray crystallographic analysis of representative Ph(2)P(E)- and Cy(2)P(E)-substituted species shows exclusively the E(syn)-(beta) configuration for the P-diphenyl substituted compounds and the Z(syn)-(beta) form for the P-dicyclohexyl derivatives, independent of the chalcogen and the nitrogen substituents. Results from a DFT analysis of model compounds fail to identify a compelling electronic argument for the observed preferences in substituent orientation, suggesting that steric factors play an important role in determining the subtle energetic differences at work in these systems.     

烯烃聚合高性能FI催化剂的进展

FI催化剂系一近几年发展起来的烯烃聚合高性能催化剂。以它的极高的活性、聚合物分子结构的可控性、多重活性聚合等特性而引人注目。本评述首先进行该催化剂的化学描述,然后分别介绍该催化剂的主要特征、活性中心结构、聚合机理和应用,重点介绍该催化剂的五大特征。     

Microwave activation of electrochemical processes: enhanced electrodehalogenation in organic solvent media

The effect of high-intensity microwave radiation focused into a "hot spot" region in the vicinity of an electrode on electrochemical processes with and without coupled chemical reaction steps has been investigated in organic solvent media. First, the electrochemically reversible oxidation of ferrocene in acetonitrile and DMF is shown to be affected by microwave-induced thermal activation, resulting in increased currents and voltammetric wave shape effects. A FIDAP simulation investigation allows quantitative insight into the temperature distribution and concentration gradients at the electrode / solution interface. Next, the effect of intense microwave radiation on electroorganic reactions is considered for the case of ECE processes. Experimental data for the reduction of p-bromonitrobenzene, o-bromonitrobenzene, and m-iodonitrobenzene in DMF and acetonitrile are analyzed in terms of an electron transfer (E), followed by a chemical dehalogenation step (C), and finally followed by another electron-transfer step (E). The presence of the "hot spot" in the solution phase favors processes with high activation barriers.     

Synthesis and structures of the [benzamidinato]3- complexes Li3(tmeda)(L1)]2 and [Li(thf)4][Li5(L2)(OEt2)2] [L1 = N(SiMe3)C(Ph)N(SiMe3) and L2 = N(SiMe3)C(C6H4-4)NPh

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L(1))(tmeda)] or [{Li(L(2))(OEt(2))(2)}(2)] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li(3)(L(1))(tmeda)] (1) or [Li(thf)(4)][Li(5)(L(2))(2)(OEt(2))(2)] (2), respectively. Their structures show that in each the [N(R(1))C(R(3))NR(2)](3-) moiety has the three negative charges largely localised on each of N, N' and R = Aryl); a consequence is that the "aromatic" 2,3- and 5,6-CC bonds of R(3) approximate to being double bonds. Multinuclear NMR spectra in C(6)D(6) and C(7)D(8) show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L(1) = N(SiMe(3))C(Ph)N(SiMe(3)); L(2) = N(SiMe(3))C(C(6)H(4)Me-4)N(Ph); tmeda = (Me(2)NCH(2)-)(2); thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.     

A Structural and Theoretical Study of the Thiophosphinite and Dithiophosphinate Anions

Two novel lithium compounds containing either the phosphorus-chalcogenide anions [Ph ₂ PS]^? or [Cy ₂ PS ₂ ]^? were isolated as decomposition products in the attempted formation of phospha(V)guanidinate anions. Lithium diphenylthiophosphinite was structurally characterized as the dimeric TMEDA adduct [Li(Ph ₂ PS)(TMEDA)] ₂ (1), in which a rare example of the κ ¹ -S bonding mode was observed for the anion. The dicyclohexyldithiophosphinate anion was incorporated into an aggregated structure with molecular formula [Li ₅ (Cy ₂ PS ₂ ) ₄ (OH)] ₂ (2). DFT calculations were performed on the isolated [R ₂ PS]^? and [R ₂ PS ₂ ]^? anions (R = Ph, Cy), indicating delocalization of electron density into the P-S bonds for each model, in agreement with bond-lengths taken from crystallographic data.     

A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d metal ions

Reaction of the hexadentate N₄O₂-donor ligand 6,6′-bis(3-hydrazonobutan-2-one)-2,2′-bipyridine (L) with Ag^(I) and Zn^(II) affords a dinuclear double stranded helicate species [Ag₂L₂]²⁺ (1a) and [Zn₂L₂]²⁺ (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV–Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of (1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag?Ag close contact of 3.034(4) Å is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N–H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH?O_keto hydrogen bonding to maintain the supramolecular structure.     

1,4-Aryl migration under copper(I) atom transfer conditions

Reaction of N-alkyl-N-(trichloroacetyl)arylsulfonamides with CuCl/amines leads to N-alkyl-N-(dichloroacetyl)-arylsulfonamides via reduction or N-alkyl-aryldichloroacetamides via 1,4-aryl migration with loss of SO₂. The ratio of reduction to aryl migration is dependent upon the temperature and the ligand utilised. Along with amide bond hydrolysis these reactions may compete when carrying out slow atom transfer radical cyclisation reactions using sulfonamides.