A series of gold(III) cations of the type cis-[CH3)2AuL2]+ X? where L Ph3, PMePh2, PMe2Ph, PMe3, AsPh3, AsPh3, SbPh3, H2NCH2CH2NH2, Ph2PCH2CH2-PPh2, Ph2AsCH2CH2AsPh2, and o-C6H4(AsMe2)2 and X BF4?, PF6?, ClO4?, and F3CSO3? has been prepared. In addition, the cis complexes [(CH3)(CD3)-Au(PPh3)2]F3CSO3, [(C2H5)2Au(PPh3)2]F3CSO and [(n-C4H9)2Au(PPh3)2]F3-CSO3 have been synthesized. All have been characterized by PMR, Raman and infrared spectroscopy. These [R2AuL2]X compounds yield only ethane, butane, or octane via reductive elimination, and no disproportionation is observed. The alkane eliminations have been studied in CHCl3, CH3Cl2, and CH3COCH3 solution as a function of temperature, concentration of the complex, and concentration of added ligand L. Elimination is fastest when L is bulky (PPh3 > PMePh2 > PMe2Ph > PMe3), decreases in the sequence SbPh3 > AsPh3 > PPh3, is slow with chelating ligands, is inhibited by excess ligand, and there is small anion effect as X is varied. As R is varied, the rate of elimination decreases Bu ? Et > Me. An intramolecular dissociative mechanism is proposed which involves rapid elimination of alkane from an electron deficient dialkylgold(III) complex with nonequivalent gold—carbon bonds and produces the corresponding [AuL2]X complex. 相似文献
Photoelectron emission microscopy in connection with magnetic circular dichroism in soft X-ray absorption can be used for
the microscopic imaging of magnetic domains in layered thin film structures consisting of several magnetic layers. Due to
the element-selectivity of the method, the different magnetic layers in such a structure can be imaged separately, provided
that they contain different elements. This has been applied for the investigation of Co/Cu/Ni trilayers, epitaxially grown
on Cu (001). The magnetic coupling between the Co and Ni layers can be directly visualized from comparing layer-resolved magnetic
domain images of both layers. As a consequence of the competition between the anisotropy energies of the two magnetic layers
and the magnetic coupling energy, spin-reorientation transitions between collinear and non-collinear magnetic configurations
are observed. Apart from this globally observable magnetic interlayer coupling a micromagnetic coupling mechanism is also
evident from the layer-resolved domain images. It is caused by magnetostatic interaction of local stray fields from domain
walls.
Received: 22 August 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-345/5511-223, E-mail: kuch@mpi-halle.de 相似文献
From the systems Cu(II)–cyclam–[M(CN)4]2? (cyclam = 1,4,8,11-tetraazacyclotetradecane; M = Ni, Pd, Pt), three cyanidocomplexes Cu(cyclam)M(CN)4 [M = Ni (1), Pd (2), Pt (3)] were isolated and characterized by chemical analysis, IR and UV–VIS spectroscopy. The three compounds are isostructural, and their crystal structures are formed by quasi-linear chains exhibiting [–Cu(cyclam)–μ–NC–M(CN)2–μ–CN–]n composition. The Cu(II) atoms reside on centres of symmetry and are coordinated in the form of an elongated octahedron with mean equatorial Cu–N bonds of 2.015(12), 2.017(13) and 2.011(11) Å in (1), (2) and (3), respectively, and weakly N-bonded bridging cyanido ligands in the axial positions [2.5321(9) Å in (1), 2.518(2) Å in (2) and 2.549(3) Å in (3)]. Hydrogen bonds of the N–H···Ncyanido···H–N type link neighbouring chains, and a topologically square network of paramagnetic Cu(II) atoms is formed. The magnetic susceptibilities of all three complexes follow the Curie-Weiss law with a weak antiferromagnetic exchange coupling below 5 K. 相似文献
A scheme of a fiber chemical sensor of amine-type compounds has been implemented. The sensor includes a film nanostructure
deposited on the end face of an optical fiber 600 μm in diameter. The film consists of luminescent silica nanoparticles modified
by functional pyrylocyanine dye, silver nanoparticles, and a photonic crystal opal film. An additional coating of the sensor
film from above by a porous selective mirror, such as a photonic crystal, and introduction of silver nanoparticles 5–7 nm
in diameter into it make it possible to increase the sensor sensitivity by an order of magnitude. 相似文献
An analytical method for the determination of the major endogenous and exogenous estrogenic steriods in effluent water samples of sewage treatment plants (STPs) with a LOQ down to 1 ng/L and below has been developed. The exogenous estrogen 17α-ethynylestradiol, frequently used as estrogenic component in oral contraceptives, and the endogenous estrogen 17β-estradiol show the highest estrogenic potential, therefore they were part of our target compounds. In addition, the content of the synthetic gestagen levonorgestrel, also often administered in oral contraceptives, was determined. A solid-phase extraction system for high volume sampling of water up to 25 L was implemented. Two types of adsorbent, Amberlite XAD 2 and a mixture of LiChrolut EN/Bondesil C-18, respectively, were tested for their extraction efficiency of these polar analytes. Recovery rates with LiChrolut EN/¶Bondesil C-18 ranged up to 94 %, whereas sampling on XAD 2 led only to poor recoveries below 40 %. After a liquid chromatographic clean-up step on silicagel the steroids were converted into their trimethylsilyl-ethers by the reaction with MSTFA/TMSI (N-methyl-N-trimethylsilyl-2,2,2-trifluoroacetamide, trimethylsilyliodide) and were then determined by HRGC/MS in the selected ion mode. A limit of quantification over the whole procedure of at least 1 ng/L was reached for all analytes. In several effluent samples the input of estrogens by the STP of the cities Ulm and New Ulm into the river Danube was characterised. The concentrations commonly found ranged from 1 ng/L up to 13 ng/L, depending on the respective steroid. 相似文献
For the first time, the successful Gilch synthesis of poly(ortho‐phenylene vinylenes) (ortho‐PPVs) is reported. The molar mass of the constitutionally homogeneous ortho‐PPVs reaches values as high as Mw ≈ 300 000 Da. The ortho‐connectivity of the repeating units forces the chains to assume closely packed conformations even in good solvents. Significant perturbation of the π–electron systems and considerable shortening of the conjugation lengths are the consequences. UV–vis absorption and photoluminescence maxima consequently are shifted clearly toward shorter wavelengths compared to, e.g., classic para‐PPVs.
The infrared spectra, elemental and thermal (TG/DTG and DTA) analyses of novel [Zn(cyclen-κ4N1,4,7,10)(HGly-κ2O,O')](ClO4)2 (1), and [Zn2(cyclen-κ4N1,4,7,10)2(μ-S-Ala-κ2N,O)](ClO4)(3)·2H2O (2) complexes (cyclen - 1,4,7,10-tetraazacyclododecane) were recorded and analyzed in the relation to their structural peculiarities. IR spectral data indicate both mono- or bidentate coordination mode of a carboxylate group in the prepared complexes (at pH≈9). The results indicate unusual bidentate carboxylate coordination mode (in complex (1)) toward to Zn2+-cyclen unit. Therefore the crystal structure determination of the crystalline complex [Zn(cyclen-κ4N1,4,7,10)(NO3-κ2O,O')](NO3) was attached in order to support the coordination mode assignment in complex (1). 相似文献
The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window. 相似文献