Kristallzüchtung und Strukturbestimmung eines metallorganischen Donator/Akzeptor‐Komplexes von I2C=CI2

Crystallization and Structure Determination of an I₂C=CI₂ organometallic Donor/Acceptor Complex The rectangular D_2h molecule I₂C=CI₂ contains 95.5% iodine with the rather bulky I substituents hiding the CC‐π‐system and heavily penetrating each other [1]. Starting both from the structure determination of a sublimed novel P2₁/n polymorph and extensive DFT calculations, numerous hitherto unknown donor/acceptor complexes of I₂C=CI₂ have been crystallized and structurally characterized [2]. Here we report the first adduct of tetraiodoethylene to a metalorganic complex, {[Pb²⁺(18‐crown‐6)(I^–)₂]…I₂C=CI₂}, crystallized from lead(18‐crown‐6)diiodide and I₂C=CI₂ in chloroform. The structure consists of polymer chains with angles ∢IPbI of 159° and distances I^–…I₂C=CI₂ between 348 to 359 pm. Both the 18‐crown‐6 ligand and the chloroform solvent molecule included in the crystal are considerably disordered. Space group Pnma (IT Nr. 62), Z = 4, lattice dimensions at 150 K, a = 1724.2(2), b = 1416.4(2), c = 1330.8(2), V = 3250.0(8) · 10⁶ pm³, R = 0.0428.     

Electron Deformation Density in Rhombohedral α‐Boron

α‐boron is the most simple structure of all boron modifications having one B₁₂ icosahedron per (rhombohedral) unit cell. The conventional, free atom crystal structure refinement with R = 6.2% indicates considerable charge redistribution into covalent bonding. In a high order‐low order and multipole refinement the R value could be reduced to 1.19%. The ensuing deformation difference density maps reveal bonding between the boron atoms, in the icosahedra and between the icosahedra.     

Physical properties and structure of thin conducting ion-beam modified polymer films

In this work, a complex investigation of the film surface composition, chemical bonding, conductivity, optical properties, density, hardness and Young's modulus of ion-beam-modified polyimide films was carried out. It was shown that the partial destruction of chemical bonding under ion bombardment leads to the formation of graphite-like, amorphous carbon islands, which increase the surface film conductivity by several orders of magnitude, from an insulating to a semiconducting region. Strong enhancements of both the conductivity and the optical absorption coefficient occur when the fraction of amorphous carbon clusters dispersed in a polyimide matrix reaches 40 %. The values of hardness, Young's modulus and density at high irradiation doses reach the values typical of a hydrogenated amorphous carbon.     

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

Past atmospheric composition can be reconstructed by the analysis of air enclosures in polar ice cores which archive ancient air in decadal to centennial resolution. Due to the different carbon isotopic signatures of different methane sources high-precision measurements of delta13CH4 in ice cores provide clues about the global methane cycle in the past. We developed a highly automated (continuous-flow) gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique for ice core samples of approximately 200 g. The methane is melt-extracted using a purge-and-trap method, then separated from the main air constituents, combusted and measured as CO2 by a conventional isotope ratio mass spectrometer. One CO2 working standard, one CH4 and two air reference gases are used to identify potential sources of isotope fractionation within the entire sample preparation process and to enhance the stability, reproducibility and accuracy of the measurement. After correction for gravitational fractionation, pre-industrial air samples from Greenland ice (1831 +/- 40 years) show a delta13C(VPDB) of -49.54 +/- 0.13 per thousand and Antarctic samples (1530 +/- 25 years) show a delta13C(VPDB) of -48.00 +/- 0.12 per thousand in good agreement with published data.     

Electrically tunable long-period fiber gratings with low-birefringence liquid crystal near the turn-around point

In this work, an electrically tunable long-period fiber grating (LPFG) coated with liquid crystal layer (LC) is presented. As a LC layer, a prototype low-birefringence 1550A LC mixture was chosen. As a LPFG host, two types of gratings were studied: the LPFGs based on a standard telecommunication fiber, produced by an electric arc technique with a period of 222 μm, and the LPFGs based on a boron co-doped fiber written by a UV technique with a period of 226.8 μm. The relatively short period of these gratings allowed exploiting unique sensing properties of the attenuation bands associated with modes close to the turn-around point. Experiments carried out showed that for the UV-induced LPFG with a LC layer, on the powered state the attenuation band could be offset from the attenuation band measured in the unpowered state by almost 130 nm. When the arc-induced LPFG was coated with the LC, the depth of the attenuation band could be efficiently controlled by applying an external E-field. Additionally, all experimental results obtained in this work were supported by the theoretical analysis based on a model developed with Optigrating v.4.2 software.     

Zur Bestimmung der Kristallitgrößenverteilung von Metallen auf Katalysatorträgern aus Röntgenweitwinkelmessungen (I). Ermittlung primärer Verteilungskenngrößen aus Linienprofilen

Possibilities are investigated to determine the size distribution of metal crystallites in supported catalysts from wide angle X-ray interferences lines. It is shown that for this a Fourier method is suitable, which primarily provides the moments of the chord distribution. From the results distribution functions for the metal crystallites can be derived, which reproduce the experimental lines with high accuracy.     

A Computational Analysis of the Reaction of SO2 with Amino Acid Anions: Implications for Its Chemisorption in Biobased Ionic Liquids

We report a series of calculations to elucidate one possible mechanism of SO₂ chemisorption in amino acid-based ionic liquids. Such systems have been successfully exploited as CO₂ absorbents and, since SO₂ is also a by-product of fossil fuels’ combustion, their ability in capturing SO₂ has been assessed by recent experiments. This work is exclusively focused on evaluating the efficiency of the chemical trapping of SO₂ by analyzing its reaction with the amino group of the amino acid. We have found that, overall, SO₂ is less reactive than CO₂, and that the specific amino acid side chain (either acid or basic) does not play a relevant role. We noticed that bimolecular absorption processes are quite unlikely to take place, a notable difference with CO₂. The barriers along the reaction paths are found to be non-negligible, around 7–11 kcal/mol, and the thermodynamic of the reaction appears, from our models, unfavorable.     

Halogen‐Free Polyarylphosphonates and Polyelectrolyte Membranes for PEMFC by Nickel‐Catalyzed Phosphonylation with Silylated Phosphates

Summary: The nickel‐catalyzed arylphosphonylation with tris(trimethylsilyl) phosphite (TMSP) is applied to brominated high‐performance (HP) polymers in weakly coordinating high temperature solvents. At elevated temperatures, this affords halogen‐free, soluble, phosphonic acid‐functionalized polyelectrolytes and an unprecedented control of the degree of phosphonylation (ds_P). Brominated polysulfone (PSU) of various degrees of bromination (ds_Br) has been phosphonylated with TMSP in diphenyl ether at 200 °C in the presence of 1–10 mol‐% NiCl₂. Upon methanolysis, arylphosphonic PSU with ds_P up to 223 mol‐% is obtained in near quantitative bromine conversion. Catalyst residues are readily removed during methanolysis. This very versatile two‐step process affords soluble arylphosphonic polymers for casting tough membrane films. In contrast to sulfonated PSU, the arylphosphonic PSU membranes exhibit improved thermal and chemical stabilities, combined with far lower water swelling in accordance with the demands of polyelectrolyte membrane fuel cell (PEMFC) applications.

Mass swelling (sw_M) in water of sulfonated (A–C) and phosphonylated PSU (D).     

Breaking the Symmetry in a Car-Following Model

A wide class of microscopic car-following traffic models deals with a system of ODEs describing N cars driving on a circular highway. The symmetry of the road naturally leads to (quasi-)stationary solutions and to an analysis of their stability. Breaking this symmetry with small perturbations we show the existence of a branch of some special solutions that occur instead of the stationary points. Those solutions can be interpreted in reality, they describe the behavior of the cars on the road as expected. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)