Sur les composes fluores du tellure (IV): Etude structurale de CsTeF5

CsTeF₅ was synthetized in hydrofluorhydric solution by action of CsF and TeO₂. The structure was solved by means of three dimensional Patterson synthesis (final R_w value = 0,033). This structure contains isolated TeF₅ groups which are distorted square pyramids (Cs symmetry). The apical Te-F bond distance and the basal Te-F bond distances are 1,81 , 1,91 and 1,95 Å respectivly.     

Etude structurale de Li2TeO4. Coordination du tellure VI et du lithium par les atomes d'oxygéne

A single crystal of Li₂TeO₄ has been prepared by hydrothermal synthesis and its structure has been determined from three-dimensional X-ray analysis. The crystals are tetragonal, space group P4₁22 with a = b = 6.045(3) Å, c = 8.290(2) Å, and Z = 4. The structure is a distorted inverse spinel with helicoidal chains of Te(VI) octahedra parallel to the [001] axis which can be formulated as [TeO₄]^2n?_n.     

CO2 adsorption in LiY and NaY at high temperature: molecular simulations compared to experiments

Grand Canonical Monte Carlo simulations combined with adsorption measurements have been carried out to gain further insight into the CO₂ adsorption process at the microscopic scale in both LiY and NaY faujasites at various temperatures. A new Li⁺−CO₂ force field derived by ab initio calculations was validated by a reasonable agreement between the simulated isotherms and those obtained by experiments in a wide range of temperature (from 323 K to 473 K). In addition, the microscopic mechanisms of CO₂ adsorption in both systems, consistent with the trends observed for the simulated differential enthalpies of adsorption as a function of the loading, were proposed. It was observed that two different types of adsorption behaviour exist for NaY and LiY at 323 K and 373 K, mainly caused by the significant more exposed position of the SII Na⁺ from the six-ring plane of the supercage compared to those occupied by the SII Li⁺, whereas at higher temperature, both faujasites exhibit the same flat profile for the differential enthalpy of adsorption as a function of loading.     

Adsorption mechanism of carbon dioxide in faujasites: grand canonical monte carlo simulations and microcalorimetry measurements

Molecular simulations have been coupled with adsorption microcalorimetry measurements in order to understand more deeply the interactions between carbon dioxide and various types of faujasite surfaces. The modeling studies, based on newly derived interatomic potentials for describing the interactions within the whole system, provide isotherms and evolutions of the differential enthalpy of adsorption as a function of coverage for DAY, NaY, and NaLSX which are in very good accordance with those obtained experimentally. The microscopic mechanism of CO2 adsorption was carefully analyzed, with different behaviors proposed, depending on the energetic characteristics of each faujasite surface, which are consistent with the trends observed for the differential enthalpies of adsorption.     

Etude structurale d'un nouveau tellurate alcalin: Na2TeO4. Evolution de la coordination du tellure(VI) et du cation quand on passe du cation lithium au sodium

Single crystal Na₂TeO₄ has been prepared by hydrothermal synthesis and its structure determined from three dimensional X-ray analysis. The crystal is monoclinic, space group $\text{P}\text{P2}{}_1\text{c}$ with a = 10.632(5)Å, b = 5.161(2)Å; c = 13.837(11)Å, and β = 103.27(4)°. The crystal structure is built up of chains of Te(VI)O₆ octahedra parallel to the [010] axis which can be formulated as [TeO₄]_n^2n?. All sodium cations are in very distorted octahedral coordination.     

Sur les chalcogeno-iodures d'antimoine SbXI(X =S,Se, Te): Structures et spectroscopie Mo¨ssbauer de121Sb

The crystal structure of SbXI(X =Se, Te) compounds has been determined by means of three-dimensional intensity data. The crystal structure of SbSeI, orthorhombic, space groupPnma witha = 8.698(2), b = 4.127(1), c = 10.412(2) Å, was refined at several temperatures (180 K,R = 0.021; 293 K,R = 0.020; 320 K,R = 0.023) in correlation with the paraelectric structure or SbSI stable above 293 K. The crystal structure of SbTeI, triclinic, space groupP1¯, witha = 7.570(3), b = 7.159(3), c = 4.228(3) Å, α = 107.22(5), β = 106.18(4), γ = 77.19(3)° has been determined by symbolic addition method and refined to a finalR value of 0.035. These structures are built up from infinite weakly linked ribbons (SbX₂)_n of trigonal SbX₃ with SbX bonds of 2.605(1), 2.795(1)Å(X =Se), and 2.829(1), 2.953(1), 2.955(1)Å(X =Te). The nature of SbX and SbI bonds is discussed in terms of the S, Se, Te substitution. Antimony-121 Mo¨ssbauer spectra have been recorded at liquid helium temperature. The data are discussed with regard to the stereochimical activity of the antimony (III) lone pair of electrons. For SbTeI the Mo¨ssbauer parameters are interpreted in terms of direct population of conductance bands by nonbonding electron pairs.     

The electrocrystallization of nickel on vitreous carbon A kinetic and structural study of nucleation and coalescence

FeOOH deposition films were formed on gold electrodes by polarization in an electrolyte containing Fe²⁺. The time dependence of the formation current suggests a diffusion-controlled formation process. The oxidation of Fe(CN)₆^4? at FeOOH films shows no Tafel-like behavior. It is assumed that the Fe²⁺ to form the film, as well as the Fe(CN)₆^4? to be oxidized, have to diffuse through an adherent, strongly hydrous layer of Fe(OH)₃ to the surface of FeOOH.     

The remarkable configurational stability of ortho,ortho-tetrafluoro substituted biphenyls: 2,2,4,4,6,6-hexafluorobiphenyl-3,3-dicarboxylic acid as a model

Optically active 2,2^′,4,4^′,6,6^′-hexafluorobiphenyl-3,3^′-dicarboxylic acid was obtained through its brucine salt. The half-life time for racemization was determined at various temperatures and the torsional barrier for racemization was calculated to be 25.4 kcal/mol. These results prove, contrary to textbook knowledge, that ortho,ortho^′-tetrafluoro substituted biphenyls are resolvable.     

Structure Cristalline du Sulfure d'Étain(II) et de Thallium(I) Tl2Sn2S3

Crystal Structure of Tl₂Sn₂S₃ The compound Tl₂Sn₂S₃ had been prepared from SnS? Tl₂S mixtures. The cell is monoclinic, space group C2/c with a = 13.887(7), b = 7.742(4), c = 7.267(4) Å, β = 105.39(3)° and Z = 4. The structure was solved by the symbolic addition method and refined by least-squares to a final R = 0.086 for the 382 observed reflections. From this structure it is apparent that Tl₂Sn₂S₃ is of defect NaCl type with the thallium and tin atoms distributed over the cation positions, the sulfur atoms and vacancies over the anion positions. Tl and Sn atoms have four bonds to S atoms of 2.81–3.13 Å and 2.68–3.11 Å respectively. The thallium and tin lone pairs of electrons are stereochemically active.