Metallorganische verbindungen der lanthanoide : LXX. Bis(cyclopentadienyl)seltenerdkomplexe: Synthese und röntgen-strukturanalyse von dem intramolekular stabilisierten lutetiumalkyl Cp2 Me2 und dem monomeren basenfreien yttriumcarboxylat Cp2Y[η-O2C(CH2)3NMe2]

Metathesis of LuCl₃, NaCp and Li(CH₂)₃NMe₂ in the molar ratio 1:2:1 affords the lutetium alkyl species Cp₂ Me₂ (1); analogous reaction of LuCl₃, NaMeC₅H₄ and LiCH₂CH(Me)-CH₂NMe₂ generates the corresponding complex (MeC₅H₄)₂ Me₂] (2). Treatment of YCl₃ with two equivalents of NaCp and one equivalent of Li(CH)₃NMe₂ yields, in the presence of CO₂, the yttrium carboxylate Cp₂Y[η²-O₂C(CH₂)₃NMe₂ (3). Mass spectrometrical studies of the solvent-free rare earth triflates [Cp₂Ln(OSO₂CF₃)]₂ (Ln = Sc (4), Lu (5)) have shown them to be dimeric. The crystal structures of 1 and 3 were determined by X-ray diffraction methods. 1 crystallizes in the monoclinic space group P2₁ (No. 4) with the unit-cell parameters a 657.0(4), b 1386.7(8), c 803.5(3) pm, β 106.64(5)°, V 704(1) × 10⁻³⁰ m³ and Z = 2. The structure was solved on the basis of 1094 observed reflections with F₀ ≥ 3σ(F₀) and refined to a final R value of 0.0483. With the short Lu---N bond length of 237(1) pm the molecular structure of 1 exhibits an intramolecular N → Lu coordination. The crystals of 3 are triclinic, space group P (No. 2), with a 1078.2(6), b 1533.0(9), c 1020.3(8) pm, α 109.47(6), β 82.75(6), γ 88.99(5)°, V 1574(2)×10⁻³⁰ m³ and Z = 4. Least-squares refinement of the model based on 1659 observed reflections converged to R = 0.093 (F₀ ≥ 5σ(F₀)). The structural data of 3 feature a monomer with a chelating carboxylate group. The long Y---N distance (499 pm) excludes any intramolecular N---Y interactions.     

Heterogeneity in styrene-butadiene latex films

Low-Tg styrene-butadiene (SB) latex films were investigated by noncontact atomic force microscopy and scanning electric potential microscopy, revealing a number of different morphologies and electric potential patterns across films cast from the same SB latex dispersions under the same conditions. Surface leveling and charge dispersion throughout the films are, thus, restrained even at temperatures above Tg and the minimum film-formation temperature. An unprecedented electric pattern is observed, in which the particle cores are more positive than the contacting particle outer layers. Different packing patterns, including cubic and hexagonal arrays, coexist in neighboring areas. Zonal centrifugation of the SB latex in sucrose density gradient shows that particles cover a broad range of densities. Thus, film surface heterogeneity is at least partly due to particle heterogeneity. Fractal dimensions of topographic profiles are lower than those of the electric potential profiles, showing that charge mobility is much more restrained than polymer chain motion at the film surface and that it imposes a limit to the charged chain-ends motion.     

Probing antiaromaticity: resonance Raman investigation of a series of differently substituted boroles

We report an investigation of four differently substituted boroles by resonance Raman (RR) spectroscopy with the aim of gaining insight into the structural changes that occur upon electronic π–π* excitation in the five‐membered BC₄ ring. Such boroles are prototypes for the theory of antiaromaticity, because the empty p_z orbital at the boron interacts with the π system of the carbon backbone to delocalize the four π electrons. The magnitude of this interaction depends on the substituents at the boron atom. In all compounds, an intense band appears around 1600 cm⁻¹, which can be assigned to a CC stretching vibration. The selective amplification of this mode indicates an expansion of the borole ring upon electronic excitation. The resonant enhancement of another mode at around 1300 cm⁻¹, which can be assigned to a vibration between the boron and the substituent, gives evidence that the degree of antiaromaticity in the borole depends strongly on the interaction between the substituent at the boron atom with the empty p_z orbital of the boron. When the boron is connected to a ferrocene, this band appears with high intensity, indicating a strong interaction between B and Fe. Furthermore, we studied the dependence of the excitation wavelength on the Raman intensities. In addition, we used DFT calculations to determine the vibrational wavenumbers. Copyright © 2009 John Wiley & Sons, Ltd.     

Equivariant closure operators and trisp closure maps

A trisp closure map ? is a special map on the vertices of a trisp (triangulated space) T with the property that T collapses onto the subtrisp induced by the image of ?. We study the interaction between trisp closure maps and group operations on the trisp, and give conditions such that the quotient map is again a trisp closure map. Special attention is on the case that the trisp is the nerve of an acyclic category, and the relationship between trisp closure maps and closure operators on posets is studied.     

LC–high resolution MS in environmental analysis: from target screening to the identification of unknowns

This article provides an overview of the state-of-the-art and future trends of the application of LC–high resolution mass spectrometry to the environmental analysis of polar micropollutants. Highly resolved and accurate hybrid tandem mass spectrometry such as quadrupole/time-of-flight and linear ion trap/orbitrap technology allows for a more reliable target analysis with reference standards, a screening for suspected analytes without reference standards, and a screening for unknowns. A reliable identification requires both high resolving power and high mass spectral accuracy to increase selectivity against the matrix background and for a correct molecular formula assignment to unknown compounds. For the identification and structure elucidation of unknown compounds within a reasonable time frame and with a reasonable soundness, advanced automated software solutions as well as improved prediction systems for theoretical fragmentation patterns, retention times, and ionization behavior are needed.     

Chloride-bridged oxovanadium(V) complexes with alkoxyalkoxide ligands. Synthesis, structure, electrochemistry and reactivities

A series of mixed alkoxyalkoxo chloro complexes of vanadium(V), [VOCl2(OCH2CH2OR)]2 (R = Me, Et, iPr, Bz), [VOCl2(OCMe2CH2OMe)]2 and [VOCl2(OCH2(cyclo-C4H7O)]2, were synthesised and characterised. The title compounds can be obtained either from VOCl3 and the alkoxyalcohols by HCl elimination or from the corresponding lithium alkoxides and VOCl3 by salt metathesis reaction. X-Ray diffraction studies revealed the title compounds to be dimers with chloride bridging ligands and intramolecular ether coordination. Electrochemical results obtained by cyclic voltammetry indicate irreversible, reductive behaviour. The interactions of the title compounds with oxygen, nitrogen and phosphorus donor ligands were examined. Phosphorus and nitrogen donors lead to reduction products whereas tetrahydrofuran coordinates to the vanadium(V) centre by breaking the chloride bridge. All tetrahydrofuran complexes, [VOCl2(OCH2CH2OR)(thf)] (R = Me, Et, iPr) and [VOCl2(OCMe2CH2OMe)(thf)], have been characterised by single-crystal X-ray diffraction. The solid-state structures of these complexes show that they consist of six-coordinate monomers. Reaction of [VOCl2(OCH2CH(2)OMe)]2 with Me3SiCH2MgCl gave [VO(CH2SiMe3)3], which has been structurally characterised. The compounds were tested as catalysts for epoxidation and polymerisation reactions. They convert unfunctionalised olefins into the corresponding epoxides with moderate activity. They are good pre-catalysts for the polymerisation of ethene and oligomerise 1-hexene.     

Analysis of airborne substances by means of microwave thermal desorption

A method has been developed to enable thermal desorption of airborne substances from solid adsorbents based on active charcoal by means of microwave energy, followed by on-line GC-FID analysis. Ceramic traps were filled with 50 mg of commercially available graphitized carbon black. Adsorption efficiency and desorption conditions for three substances covering a broad range of vapor pressure were investigated. The recovery rate, breakthrough, and linearity of the system were determined by direct fortification with standard solutions, followed by microwave thermal desorption and gas chromatographic separation. The recovery efficiencies were 80–84 %, with a standard deviation of 3–6 %. The correlation coefficient of the linear range between 1 (10 for one of the compounds) and 1000 ng was > 0.999. Initial experiments were performed to investigate the enrichment of the standards from the gaseous state. The recovery rates of the most volatile compound was increased by optimizing the density of the packing.