Structural, vibrational study and conductivity investigation of a new cesium–bismuth polyphosphate CsBi(PO3)4

Synthesis, a complete structural characterization by X-ray diffraction, IR-Raman, and conductivity investigation are given for cesium–bismuth polyphosphate CsBi(PO₃)₄. This compound crystallizes in the monoclinic system with a space group P2₁/n (structural type IV). The structure consists of a three-dimensional framework made up of spiral (PO₃)_n chains linked by BiO₈ polyhedra. Two infinite (PO₃)_n chains with a period of eight tetrahedra run along the [101] direction. The infrared and the Raman spectra show clearly some characteristic bands of infinite chain structures of PO₄ tetrahedra linked by bridge oxygen. The thermo-differential analysis shows two endothermic peaks at T₁?=?448 and T₂?=?919 K. No weight loss was observed in the (TGA) until the temperature 800 K. The conductivity measurements confirm the presence of a phase transition at 448 K accompanied by an important increasing of the conductivity of Cs⁺ cations and a significant decreasing of the activation energy.     

Synthesis and evaluation of a broad range of new chiral phosphine–carbene ligands for asymmetric hydrogenation

A straightforward and gram scale synthesis (six-step synthesis from enantioenriched β-hydroxy esters) of new structurally simple phosphine-carbene ligands bearing a single stereogenic centre has been achieved. Enantioselectivities of up to 60-63% could be achieved in the hydrogenation of methylstilbene and dehydroaminoacids when the reactions were performed under 20-50 bar hydrogen pressure.     

Numerical and experimental study of two turbulent opposed plane jets

The turbulent interaction between two opposed plane jets separated by a distance H is experimentally studied by using a PIV (Particle Image Velocimetry) method and numerically investigated by means of a finite volume code. Two turbulence models have been tested: the standard k-ɛ model and a second-order model. The validation of the numerical study was performed by comparing the results with experimental data obtained for the case of two interacting opposed jets at ambient temperature (isothermal case). The effect of the angle of inclination of the jets is studied. Conclusions of the validation are then used to study the interaction between two jets, one being maintained at ambient temperature whereas the other is heated. Results show that the stagnation point moves towards the heated jet. It is shown that the heating induces a stabilizing effect on the flow.     

Synthesis and Study of the Anodic Behavior of 1,3,4,6-Tetraaryl-2λ 4 δ 2 -thieno[3,4-c]thiophenes

Two heterocyclic compounds based on the thieno[3,4-c]thiophene structure with four aryl substituents were prepared and their behavior in electrooxidation studied. These tetraarylthieno[3,4-c]thiophenes were synthesized in three steps starting from 1,3-dibenzoylmethane in the case of 1,3,4,6-tetraphenyl-2 u 4 i 2 -thieno[3,4-c]thiophene 1a and from 1,3-bis(4'-methoxyphenyl)propane-1,3-dione in the case of 1,3,4,6-tetrakis(4'-methoxyphenyl)-2 u 4 i 2 -thieno[3,4-c]thiophene 1b , a new compound. Both cyclic and hydrodynamic voltamperometric analyses indicate two reversible one-electron oxidation stages for compound 1b , while for compound 1a only the first stage is reversible. The preparative electrooxidation of the two compounds results in the opening of one thiophene ring giving rise to n -keto-thioketones.     

Crystal architecture and thermal decomposition of two new organically templated cadmium sulfates

Two organic-inorganic hybrid compounds (C₅H₁₄N₂)[Cd(H₂O)₆](SO₄)₂ (I) and R-(C₅H₁₄N₂)×[Cd(H₂O)₆](SO₄)₂ (II) are synthesized by the slow evaporation method and characterized by single crystal X-ray diffraction, thermogravimetry, temperature-dependent X-ray diffraction, and infrared spectroscopy. The first compound crystallizes in the centrosymmetric space group P2₁/n with the following unit cell parameters: a = 6.6208(2) Å, b = 10.6963(3) Å, c = 12.9318(4) Å, V = 893.05(6) ų, and Z = 2. Its structure is solved by direct methods and refined by the least-squares analysis [R ₁ = 0.0389 and wR ₂ = 0.0821]. This compound shows a crystallographic disorder II destroys the inversion symmetry and leads to a fully ordered structure. Indeed, compound II crystallizes in the non-centrosymmetric space group P2₁ with the following unit cell parameters: a = 6.6306(1) Å, b = 10.7059(2) Å, c = 12.9186(1) Å, V = 894.67(2) ų, and Z = 2. The crystal structure of both compounds is built from isolated SO ₄ ^2? anions, disordered 2-methylpiperazinediium, (C₅H₁₄N₂)²⁺ in compound I or R-2-methylpiperazinediium R-(C₅H₁₄N₂)²⁺ in compound II, and divalent metal cations surrounded by six water molecules. These different entities are connected together only by a 3D hydrogen bond network. The thermodiffractometry and the thermogravimetric analyses indicate that the decomposition of the supramolecular precursors proceeds through several stages leading to cadmuim oxide.     

On the Stokes system and on the biharmonic equation in the half‐space: an approach via weighted Sobolev spaces

In this paper, we investigate the Stokes system and the biharmonic equation in a half‐space of ?ⁿ. Our approach rests on the use of a family of weighted Sobolev spaces as a framework for describing the behaviour at infinity. A complete class of existence, uniqueness and regularity results for both the problems is proved. The proofs are mainly based on the principle of reflection. Copyright © 2002 John Wiley & Sons, Ltd.     

Structure,thermal behavior,and dielectric properties of new cesium hydrogen sulfate arsenate: Cs<Subscript>2</Subscript>(HSO<Subscript>4</Subscript>)(H<Subscript>2</Subscript>AsO<Subscript>4</Subscript>)

Synthesis and structural characterization by single-crystal X-ray diffraction method, thermal behavior, and electrical proprieties are given for a new compound with a superprotonic phase transition Cs₂(HSO₄)(H₂AsO₄). The title compound crystallizes in the monoclinic system with the P2₁/n space group. The structure contains zigzag chains of hydrogen-bonded anion tetrahedra that extend in the [010] direction. Each tetrahedron is additionally linked to a tetrahedron neighboring chain to give a planar structure with hydrogen-bonded sheets lying parallel to (10ī). The existence of O–H and (S/As)–O bonds in the structure at room temperature has been confirmed by IR and Raman spectroscopy in the frequency ranges 4000–400 cm^?1and 1200–50 cm^?1, respectively. Differential scanning calorimetry analysis of the superprotonic transition in Cs₂(HSO₄)(H₂AsO₄) showed that the transformation to high temperature phase occurs at 417 K by one-step process. Thermal decomposition of the product takes place at much higher temperatures, with an onset of approximately 534 K. The superprotonic transition was also studied by impedance and modulus spectroscopy techniques. The conductivity in the high temperature phase at 423 K is 1.58 × 10^?4 Ω^?1 cm^?1, and the activation energy for the proton transport is 0.28 eV. The conductivity relaxation parameters associated with the high disorder protonic conduction have been examined from analysis of the M”/M”_max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to the proton hopping mechanism.     

Role of iron in Na <Subscript>1.5</Subscript>Fe <Subscript>0.5</Subscript>Ti <Subscript>1.5</Subscript>(PO <Subscript>4</Subscript>) <Subscript>3</Subscript>/C as electrode material for Na-ion batteries studied by operando Mössbauer spectroscopy

The role of iron in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃/C electrode material for Na batteries has been studied by ⁵⁷Fe Mössbauer spectroscopy in operando mode. The potential profile obtained in the galvanostatic regime shows three plateaus at different voltages due to different reaction mechanisms. Two of them, at 2.2 and 0.3 V vs Na ⁺/Na ⁰, have been associated to redox processes involving iron and titanium in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃. The role of titanium was previously elucidated for NaTi ₂(PO ₄)₃ and the effect of the substitution of Fe for Ti was investigated with ⁵⁷Fe Mössbauer spectroscopy. We show that iron is an electrochemically active center at 2.2 V with the reversible Fe ³⁺/Fe ²⁺ transformation and then remains at the oxidation state Fe ²⁺ along the sodiation until the end of discharge at 0 V.     

The spectrum of a weighted Laplacian in the half‐space

J. Banasiak In this paper, we deal with spectral properties of a weighted Laplacian in the half‐space when a Dirichlet or a Neumann boundary condition is imposed. After proving that the spectrum is discrete under suitable assumptions, we give explicit formulae of eigenvalues and eigenfunctions in a specific case. In particular, the obtained eigenfunctions are rational or pseudo‐rational and have remarkable orthogonality properties. These results suggest the use of the discovered functions for approximating solutions of elliptic problems in the half‐space. Copyright © 2015 John Wiley & Sons, Ltd.     

Polyvinylpyrrolidone Behavior in Water/Ethanol Mixed Solvents: Comparison of Modeling Predictions with Experimental Results

The objective of this work is to study the behavior of a neutral polymer, polyvinylpyrrolidone (PVP), in a mixture of water and ethanol. A comparison of the experimental results with a theoretical model of effective solvent interaction with polymer (ESIP) was made. To do so, dynamic light scattering experiments were used to measure the hydrodynamic radius of PVP (M _w = 3.6 × 10⁵ g·mol^?1) as a function of the ethanol fraction, x _A, in the medium at 25 °C. We show that the polymer adopts an ideal chain–globule–coil conformation transition as the ethanol molar fraction varies. This transition is attributed to the change of the solvent quality which results from water and ethanol complex formation. On the other hand, the ternary PVP/water/ethanol system was described by the ESIP model. From the polymer–effective solvent interaction, the second virial coefficient of the polymer/effective solvent and the preferential adsorption parameter were calculated. The obtained results are in agreement with the reported experiments.