Surface modifications of illite in concentrated lime solutions investigated by pyridine adsorption

The surface properties and functionality of an illite-containing clay mineral in alkaline solutions containing increasing quantities of calcium hydroxide were investigated using FTIR monitored pyridine adsorption at various temperatures. Results showed that the binding behavior of electron donor pyridine molecules to illite platelets is mostly governed by electron acceptor sites located at the edges of the clay particles. The binding of bulky hydrated calcium ions at the surface of the illite platelets decreases the surface area of illite. Moderate thermal treatments up to 450 °C do not affect the structure of the clay mineral but strongly decrease the number of Lewis and Brönsted sites available at the edges of the clay platelets.     

High resonant reflection of a confined free space beam by a high contrast segmented waveguide

High resonant reflection of a free space wave from a deeply corrugated slab waveguide is shown to take place in the case of a focused free space beam under normal incidence. It is described as a result of a strong intra-guide coupling coefficient allowing the coupled wave to be closely localized under the incident beam, therefore to interfere with it with high contrast effects. The coupled mode inspired analysis gives the possibility of optimizing the resonant structure; it is related and compared with the photonic crystal vision of the same functional structure to which it confers more intelligibility.     

Misfit dislocations in limited inhomogeneous media: A review

Elastic fields of translation and misfit dislocations (resp. TD's and MD's) are investigated for two types of inhomogeneous materials.First, a multilayer formed by parallel heterointerfaces or free surfaces and containing one periodic array of interfacial MD's. In the more simple case of a thin layer on a substrate, analytic solutions can be found for the displacement field u relative to a single or a hexagonal periodic array of MD's. In the less simple case of a thin bicrystal and a layer sandwiched between two semi-infinite media, explicit solutions can still be extracted. For the general case of a multilayer material which involves a number N>2 heterointerfaces, analytic expressions become intractable. Solutions can nevertheless be obtained from the numerical inversion of linear equations which express the limiting boundary conditions along the heterointerfaces.Second, a thin bicrystal containing an heterointerface perpendicular to the two free surfaces of a foil. Starting from the elastic field of an edge TD parallel to the free surfaces, it is shown how to derive that of (i) a coherent heterointerface, (ii) a semicoherent heterointerface containing a single MD, and (iii) two close and parallel coherent heterointerfaces. Numerical calculations and graphs illustrate the solutions for metals (Al, Al₂Cu), semiconductor materials (CoSi₂, Si, GaAs), thin foils of the GaAs/Si type and a / superalloy.     

Hindered rotation around the aryl-to-nitrogen bond of n-acetyl,n-ethoxycarbonylmethyl-2-amino, 5-nitrothiophen

Two stereoisomers of the title compound are observed by H NMR at 10°. Their spectra coalesce at higher temperature (10°-90°). The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodynamic functions are: K(25°)= 0.170; k(25°)=23.2s^?1; ΔH_R and ΔH^≠=4.94 and 17.9 kcal.mol.^?1; ΔS_R and ΔS^≠ =13.1 and 7.7 e.u, in a 0.2 molar solution in 1,4-dioxane. The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups. The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.     

Organometallic early lanthanide clusters: syntheses and X-ray structures of new monocyclopentadienyl complexes

The reaction of Ln(BH(4))(3)(THF)(3) or LnCl(3)(THF)(3) with 1 equiv of KCp*' ligand (Cp' = C(5)Me(4)n-Pr) afforded the new monocyclopentadienyl complexes Cp*'LnX(2)(THF)(n) (X = BH(4), Ln = Sm, n = 1, 1a, Ln = Nd, n = 2, 1b; X = Cl, Ln = Sm, n = 1, 3a) and [Cp*'LnX(2)](n') (X = BH(4), n' = 6, Ln = Sm, 2a, Ln = Nd, 2b; X = Cl, Ln = Nd, 4b). All these compounds were characterized by elemental analysis and (1)H NMR. Crystals of mixed borohydrido/chloro-bridged [Cp*'(6)Ln(6)(BH(4))(12-x))Cl(x)(THF)(n')] (x = 10, n' = 4, Ln = Sm, 2a', Ln = Nd, 2b'; x = 5, n = 2, Ln = Sm, 2a' ') were also isolated. Compounds 2a, 2b, 2a', 2b', and 2a' were structurally characterized; they all exhibit a hexameric structure in the solid state containing the [Cp*(3)Ln(3)X(5)(THF)] building block. The easy clustering of THF adducts first isolated is illustrative of the well-known bridging ability of the BH(4) group. Hexameric 2a was found to be unstable in the presence of THF vapors; this may be correlated to the opening of unsymmetrical borohydride bridges observed in the molecular structure.     

Spin crossover of ferric complexes with catecholate derivatives. Single-crystal X-ray structure, magnetic and Mössbauer investigations

Complexes of general formula [(TPA)Fe(R-Cat)]X.nS were synthesised with different catecholate derivatives and anions (TPA = tris(2-pyridylmethyl)amine, R-Cat2- = 4,5-(NO2)2-Cat2- denoted DNC(2-); 3,4,5,6-Cl4-Cat2- denoted TCC2-; 3-OMe-Cat(2-); 4-Me-Cat(2-) and X = BPh4-; NO3-; PF6-; ClO4-; S = solvent molecule). Their magnetic behaviours in the solid state show a general feature along the series, viz., the occurrence of a thermally-induced spin crossover process. The transition curves are continuous with transition temperatures ranging from ca. 84 to 257 K. The crystal structures of [(TPA)Fe(DNC)]X (X = PF6-; BPh4-) and [(TPA)Fe(TCC)]X.nS (X = PF6-; NO3- and n= 1, S = H2O; ClO4- and n= 1, S = H2O; BPh4- and n= 1, S = C3H6O) were solved at 100 (or 123 K) and 293 K. For those two systems, the characteristics of the [FeN(4)O(2)] coordination core and those of the dioxolene ligands appear to be consistent with a prevailing Fe(III)-catecholate formulation. This feature is in contrast with the large quantum mixing between Fe(III)-catecholate and Fe(II)-semiquinonate forms recently observed with the more electron donating simple catecholate dianion. The thermal spin crossover process is accompanied by significant changes of the molecular structures as shown by the average variation of the metal-ligand bond distances which can be extrapolated for a complete spin conversion from ca. 0.123 to 0.156 A. The different space groups were retained in the low- and high-temperature phases.