Über die Synthese und spektroskopische Charakterisierung von Strontium‐ und Bariumtetrabromoferrat(III) und die Kristallstruktur von Ba(FeBr4)2

Preparation and Spectroscopic Characterization of Strontium and Barium Tetrabromoferrate(III) and the Crystal Structure of Ba(FeBr₄)₂ The synthesis of the hitherto unknown bromoferrates(III) of alkaline‐earth metals was carried out by heating mixtures of the metals or the binary bromides together with bromine at temperatures of 450 °C and pressures of up to 1500 bar in closed quartz ampoules. The attempts have been successful only with the larger cations of Sr and Ba. In the case of Be, Mg, and Ca only mixtures of the binary bromides with FeBr₃ could be received. By analysis of the Raman and electronic spectra the dark red compounds of Sr and Ba have been characterized as ternary tetrabromoferrates(III) containing tetrahedral FeBr₄ anions. The composition M(FeBr₄)₂ (M = Sr, Ba) has been determined by potentiometric and titrimetric analysis and thermal degradation by thermogravimetry. A single crystal structure determination of Ba(FeBr₄)₂ confirmed the spectroscopic assignments. The orthorhombic crystal structure (space group Pbca; a = 13.054(3) Å; b = 11.093(2) Å; c = 21.764(4) Å; Z = 8) consists of FeBr₄ and BaBr₉ polyhedra.     

A lower bound on the independence number of arbitrary hypergraphs

We present a lower bound on the independence number of arbitrary hypergraphs in terms of the degree vectors. The degree vector of a vertex v is given by d(v) = (d₁(v), d₂(v), …) where d_m(v) is the number of edges of size m containing v. We define a function f with the property that any hypergraph H = (V, E) satisfies α(H) ≥ Σ_v∈V f(d(v)). This lower bound is sharp when H is a match, and it generalizes known bounds of Caro/Wei and Caro/Tuza for ordinary graphs and uniform hypergraphs. Furthermore, an algorithm for computing independent sets of size as guaranteed by the lower bound is given. © 1999 John Wiley & Sons, Inc. J Graph Theory 30: 213–221, 1999     

Die Struktur von [Li(tmeda)2][Zn(2,4,6-i-Pr3C6H2)3]

X-Ray Structure of [Li(tmeda)₂][Zn(2,4,6- i Pr₃C₆H₂)₃] A side reaction of zinc halide containing VCl₂(tmeda)₂ and Li(2,4,6-iPr₃C₆H₂) formed [Li(tmeda)₂][Zn(2,4,6-iPr₃C₆H₂)₃] · 0,5[(tmeda)Li(μ-Cl)]₂. The crystal structure (orthorhombic, Pbca, a = 26,226(2), b = 19,739(2), c = 27,223(5) Å, Z = 8, R = 0,062, wR² = 0,154) contains trigonal planar zinc anions with Zn–C distances of 2,039(7) Å (average) and a propeller like arrangement of the aryl rings.     

The F NMR spectrum of bis-trifluoromethylmercury Hg(CF3)2 in the nematic phase: DAISY — a novel program system for the analysis and simulation of NMR spectra

The ¹⁹F NMR spectrum of bis-trifluoromethylmercury in the nematic phase has been analysed using the DAISY program system. The scalar and the dipolar coupling constants have been obtained.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 60. Darstellung und Eigenschaften von Zirconocendibenzylen — Molekülstruktur von (Me3SiC5H4)2Zr(CH2C6H5)2

Contributions to the Chemistry of Transition Metal Alkyl Compounds. 60 Synthesis and Properties of Zirconocene Dibenzyl Compounds — Molecular Structure of (Me₃SiC₅H₄)₂Zr(CH₂C₆H₅)₂ It is reported about the synthesis and n.m.r. spectroscopic characterization of zirconocene dibenzyl compounds with substituted cyclopentadienyl rings and the influence of the substituents on the Zr? CH₂ bonds. The molecular structure of (Me₃SiC₅H₄)₂Zr · (CH₂C₆H₅)₂ is reported and discussed.     

The influence of electronic modifications on rotational barriers of bis‐NHC‐complexes as observed by dynamic NMR spectroscopy

There has been much debate about the σ‐donor and π‐acceptor properties of N‐heterocyclic carbenes (NHCs). While a lot of synthetic modifications have been performed with the goal of optimizing properties of the catalyst to tune reactivity in various transformations (e.g. metathesis), direct methods to characterize σ‐donor and π‐acceptor properties are still few. We believe that dynamic NMR spectroscopy can improve understanding of this aspect. Thus, we investigated the intramolecular dynamics of metathesis precatalysts bearing two NHCs. We chose four systems with one identical NHC ligand (N,N′‐Bis(2,4,6‐trimethylphenyl)‐imidazolinylidene (SIMes) in all four cases) and NHC_ewg ligands bearing four different electron‐withdrawing groups (ewg). Both rotational barriers of the respective Ru‐NHC‐bonds change significantly when the electron density of one of the NHCs (NHC_ewg) is modified. Although it is certainly not possible to fully dissect σ‐donor and π‐acceptor portions of the bonding situations in the respective Ru‐NHC‐bond via dynamic NMR spectroscopy, our studies nevertheless show that the analysis of the rotation around the Ru‐SIMes‐bond can be used as a spectroscopic parameter complementary to cyclic voltammetry. Surprisingly, we observed that the rotation around the Ru‐NHC_ewg‐bond shows the same trend as the initiation rate of a ring‐closing metathesis of the four investigated bis‐NHC‐complexes. Copyright © 2013 John Wiley & Sons, Ltd.     

Internal conversion in energy dispersive X-ray analysis of actinide-containing materials.

The use of X-ray elemental analysis tools like energy dispersive X-ray (EDS) is described in the context of the investigation of nuclear materials. These materials contain radioactive elements, particularly alpha-decaying actinides that affect the quantitative EDS measurement by producing interferences in the X-ray spectra. These interferences originating from X-ray emission are the result of internal conversion by the daughter atoms from the alpha-decaying actinides. The strong interferences affect primarily the L X-ray lines from the actinides (in the typical energy range used for EDS analysis) and would require the use of the M lines. However, it is typically at the energy of the actinide's M lines that the interferences are dominant. The artifacts produced in the X-ray analysis are described and illustrated by some typical examples of analysis of actinide-bearing material.     

Darstellung und Reaktionen von Natriumtellurid,Na2Te – Kristallstruktur von [Na(CH3OH)3]2Te2

Preparation and Reactions of Sodium Telluride, Na₂Te – Crystal Structure of [Na(CH₃OH)₃]₂Te₂ Sodium telluride, Na₂Te 1 , is easily obtained by reaction of sodium with hexagonal tellurium in 1,2-dimethoxy-ethane in the presence of catalytic amounts of naphthalene. Upon exposure to oxygen 1 reacts with methanol forming [Na(CH₃OH)₃]₂Te₂ 2 , which crystal structure was determined. Compound 1 , prepared in situ, can be conveniently converted into dialkyl tellurides, R₂Te (R = C₂H₅, i-C₃H₇, CH₂ = CH? CH₂ 3 ).