Intermolecular association in liquid N-methylacetamide as studied by x-ray scattering

A structural investigation of liquid N methylacetamide was performed at 308 K using x-ray scattering. To extract the molecular form factor F1(q), the geometry of the conformer which has been found in the crystal is considered. The intermolecular structure function DM(q) is interpreted in terms of H-bonding interactions. The crystal N...O distance is taken into accounted and the number of H bond(s) is assumed to be, respectively, equal to one and two. The liquid structure can be described by a linear dimer or chainlike trimer similar to the ones existing in the crystal. The structure factors SM(q) extracted from these clusters fairly agree with the experimental one beyond q=2.5 A(-1).     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4O,1 LiFe5O8: C. Chaumont and J.C. Bernier,Départment Science des Matériaux,Ecole Nationale Supérieure de Chimie de Strasbourg, 1, rue Blaise Pascal,B.P. 296/R8, 67008 Strasbourg Cédex,France

The LiPO₃-La(P₃O₉) system was studied by microdifferential thermal analysis. The only new compound observed in the system was LiLa(PO₃)₄, melting incongruently at 960°C. A eutectic appears at 640°C, for the mixture containing 5 mole% LaP₃O₉. Crystallographic data and powder diagrams of the new compound are given. The LiLa(PO₃)₄ is an LiNd(PO₃)₄ isotype. It crystallises in the monoclinic system C2/c with a unit cell a = 16.53 (3), b = 7.08 (3), c = 9.88 (2) Å, β = 126.42 (5), and Z = 4.     

Critical aggregation concentration in mixed solutions of anionic polyelectrolytes and cationic surfactants

We have examined the polymer/surfactant interaction in mixed aqueous solutions of cationic surfactants and anionic polyelectrolytes combining various techniques: tensiometry, potentiometry with surfactant-selective electrodes, and viscosimetry. We have investigated the role of varying polymer charge density, polymer concentration, surfactant chain length, polymer backbone rigidity, and molecular weight on the critical aggregation concentration (Cac) of mixed polymer/surfactant systems. The Cac of these systems, estimated from tensiometry and potentiometry, is found to be in close agreement. Different Cac variations with polymer charge density and surfactant chain length were observed with polymers having persistence lengths either smaller or larger than surfactant micelle size, which might reflect a different type of molecular organization in the polymer/surfactant complexes. The surfactant concentration at which the viscosity starts to decrease sharply is different from the Cac and probably reflects the polymer chain shrinkage due to surfactant binding.     

Structural characterization,thermal, ac conductivity and dielectric properties of (C7H12N2)2[SnCl6]Cl2·1.5H2O

(C₇H₁₂N₂)₂[SnCl₆]Cl₂·1.5H₂O is crystallized at room temperature in the monoclinic system (space group P2₁/n). The isolated molecules form organic and inorganic layers parallel to the (a, b) plane and alternate along the c-axis. The inorganic layer is built up by isolated SnCl₆ octahedrons. Besides, the organic layer is formed by 2,4-diammonium toluene cations, between which the spaces are filled with free Cl^? ions and water molecules. The crystal packing is governed by means of the ionic N—H···Cl and Ow—H···Cl hydrogen bonds, forming a three-dimensional network. The thermal study of this compound is reported, revealing two phase transitions around 360(±3) and 412(±3) K. The electrical and dielectric measurements were reported, confirming the transition temperatures detected in the differential scanning calorimetry (DSC). The frequency dependence of ac conductivity at different temperatures indicates that the correlated barrier hopping (CBH) model is the probable mechanism for the ac conduction behavior.     

Synthesis and X-ray structure of cationic methallyl palladium complexes supported by unsymmetrical β-diimine ligands

Treatment of the unsymmetrical β-iminoamine ligands [PhCN(Ar)CHCNH(Ar)Me] with the zerovalent complex Pd(dba)₂ in the presence of the methallyloxyphosphonium salt, gives high yields of the cationic β-diimine complexes [PhCN(Ar)CH₂CN(Ar)(Me)Pd(η³-C₄H₇)]⁺[PF₆]⁻ (Ar = 2-Me-C₆H₄ (7); 2-MeO-C₆H₄ (8); 2,6-Me₂-C₆H₃ (9); 2,6-iPr₂-C₆H₃ (10)). All the new complexes have been characterised by NMR and IR spectroscopy. The structure of the cationic methallyl palladium complex (10) has been solved by X-ray crystallography.     

Circularly Polarized Fluorescent Helicene-Boranils: Synthesis,Photophysical and Chiroptical Properties

Mono- and di-boranil-substituted helicenes were prepared by BF₂-borylation of the corresponding anils, readily synthesized by condensation of 2-amino- and 2,15-diamino-helicenes with 4-(diethylamino)salicylaldehyde. After enantiomeric resolution using HPLC, their chiroptical properties including circularly polarized fluorescence in solution and in PMMA films were investigated and rationalized with the help of NMR, X-ray and quantum-chemical calculations.     

Band gap structures in underwater screens of periodically spaced porous plates

Acoustic properties of different periodic structures composed of alternating fluid and fluid-saturated porous layers obeying Biot’s theory are investigated. At first, the network of modes and the transmission coefficients of finite structures of six plates are studied in the frequency-angle of incidence plane. It is shown that the network of modes concentrates in localized domains of the plane where the transmission coefficients will take the greatest values. With this minimum of six plates, the structures exhibit the main features as for structures containing more plates, especially those with an infinite number of plates. Then, considering infinite structures the band gap calculations are led using the Bloch–Floquet theorem. The evanescent and propagative zones in the frequency-angle of incidence plane are determined. What is proposed here is a class of underwater porous screens that exhibits band gaps extending over great angular domains and enlarging in the frequency domain when the pores at the interfaces of the porous plates are sealed. The effect of porosity on the band gaps is also investigated.     

Conductivity study by complex impedance spectroscopy of solid solution AgxK1 − xNb4AsO13 (x = 0.2 and 0.62): effect of the substitution of K+ by Ag+ cations on the ionic conduction properties

Journal of Solid State Electrochemistry - Crystals of Ag0.2K0.8Nb4AsO13 (I) and Ag0.62K0.38Nb4AsO13 (II) were synthesized by a solid-state reaction. Both of them crystallize in the orthorhombic...     

Reconstruction of a defect in an open waveguide

The paper is concerned with the reconstruction of a defect in the core of a two-dimensional open waveguide from the scattering data. Since only a finite numbers of modes can propagate without attenuation inside the core, the problem is similar to the one-dimensional inverse medium problem. In particular, the inverse problem suffers from a lack of uniqueness and is known to be severely ill-posed. To overcome these difficulties, we consider multi-frequency scattering data. The uniqueness of solution to the inverse problem is established from the far field scattering information over an interval of low frequencies.