Phosphorus-bearing axially chiral biaryls by catalytic asymmetric cross-cyclotrimerization and a first application in asymmetric hydrosilylation

A novel and efficient, two-step route to axially chiral biaryls is demonstrated. In a direct asymmetric cross-cyclotrimerization in the presence of a chiral cobalt(I) catalyst, axially chiral biaryls bearing phosphoryl moieties have been prepared, and through indirect evidence the authors have been able to clarify the origin of the stereochemical induction and the nature of the central intermediate in the catalytic cycle. By subsequent reduction of the phosphoryl moiety to the corresponding phosphine, a very efficient and atom-economical approach to chiral systems has been developed. These chiral systems clearly have great potential use as axially chiral monodentate P- or bidentate P,O-ligands, as has been demonstrated by the employment of the novel NAPHEP as a new monodentate acting ligand in an asymmetric hydrosilylation reaction.     

(C3H4N2)2Au]Cl--a bis protic gold(I)-NHC

The gold(I) bis-NHC (NHC = imidazol-2-ylidene) parent compound was synthesised in high yield by a three step reaction starting from imidazole. The compound is highly water soluble and stable in concentrated hydrochloric acid.     

ChemInform Abstract: Synthesis of [(SnSe)1.15]m(TaSe2)n Ferecrystals: Structurally Tunable Metallic Compounds.

The title ferecrystals (fere: Latin, almost) with 1 ≤ n,m ≤ 6 and n and m varied independently are prepared by physical vapor deposition of the elements followed by annealing at 400 °C for 30 min.     

Electron spin resonance shift in spin ladder compounds

We analyze the effects of different coupling anisotropies in a spin-1/2 ladder on the electron spin resonance (ESR) shift. Combining a perturbative expression in the anisotropies with density matrix renormalization group computation of the short range correlations at finite temperature, we provide the full temperature and magnetic field evolution of the ESR paramagnetic shift. We show that for well chosen parameters the ESR shift can be in principle used to extract quantitatively the anisotropies and, as an example, discuss the material BPCB.     

The impedance caused by interfacial current constriction: a case study on BaF<Subscript>2</Subscript>/YSZ bicrystals

Abstract  BaF₂/YSZ (yttria stabilized zirconia) bicrystals are investigated by means of impedance spectroscopy. The spectra show two semicircles in the complex impedance plane, and both arcs exhibit very similar temperature dependences. The high frequency semicircle can be attributed to the ideal (quasi one-dimensional) bulk resistance of BaF₂, and the low frequency arc is caused by an additional resistance in BaF₂ due to the current constriction taking place close to the contact spots at the imperfect bicrystal interface. This interpretation is supported by finite element calculations revealing that bicrystals with imperfect contacts indeed exhibit an additional semicircle in the complex impedance plane even without any ion transfer resistance between the two crystals. The low frequency arc of the BaF₂/YSZ bicrystal drastically increases upon bias voltage, but relaxes to its original value after removing the bias. This phenomenon can be associated with a strong decrease of the vacancy concentration in YSZ (close to the interfacial contact spots), which is caused by F⁻ ions being pumped into YSZ and acting as a counter dopant to Y³⁺. Graphical Abstract        

Development of a usability scale based on the three ISO 9241-11 categories “effectiveness,” “efficacy” and “satisfaction”: a technical note

Accreditation and Quality Assurance - An emerging intervention in the area of dementia therapy is serious gaming. Serious gaming is understood as any meaningful use of computerized game whose chief...     

A Perturbation Result for Dynamical Contact Problems

This paper is intended to be a first step towards the continuous dependence of dynamical contact problems on the initial data as well as the uniqueness of a solution. Moreover, it provides the basis for a proof of the convergence of popular time integration schemes as the Newmark method. We study a frictionless dynamical contact problem between both linearly elastic and viscoelastic bodies which is formulated via the Signorini contact conditions. For viscoelastic materials fulfilling the Kelvin-Voigt constitutive law, we find a characterization of the class of problems which satisfy a perturbation result in a non-trivial mix of norms in function space. This characterization is given in the form of a stability condition on the contact stresses at the contact boundaries. Furthermore, we present perturbation results for two well-established approximations of the classical Signorini condition: The Signorini condition formulated in velocities and the model of normal compliance, both satisfying even a sharper version of our stability condition.     

NaPr9S2[SiO4]6: Ein Sulfidsilicat des Praseodyms mit Bromapatitstruktur

NaPr₉S₂[SiO₄]₆: A Sulfide Silicate of Praseodymium with the Structure of Bromapatite NaPr₉S₂[SiO₄]₆ is obtained as pale green single crystals of hexagonal columnar shape from reactions of Pr, Pr₆O₁₁, S, SiO₂ and NaCl (850°C, 7 d) in fused evacuated silica tubes. The crystal structure (hexagonal, P6₃/m, Z = 1, a = 981.05(4), c = 689.68(2) pm) corresponds with a modified bromapatite structure where orthosilicate ([SiO₄]^4?) and sulfide (S^2?) anions provide coordination numbers of eight and nine to the two crystallographically different cations. These occupy the positions 4 f (Na⁺ together with Pr³⁺ in a molar ratio of 1:3) and 6h (Pr³⁺ only) to realize an average Ca₅Br[PO₄]₃-type structure.