Synthèse de dérivés imidazopyridiniques et pyridinotriaziniques

Propargylpyridiniums 2-substituted by hydroxylamine or hydrazine moieties cyclize by heating to imidazopyridiniums whereas derivatives substituted by methylhydrazine or N,N' -dimethylhydrazine lead to pyridino-as-triaziniums. These differences are discussed.     

Synthesis of selenolates from stannyl and silyl alkylselenides

Stannyl and silyl alkylselenides have been efficiently transformed to the corresponding alkylselenolates on reaction with butyllithiums. Other conditions proved to be limited.     

The number of finitely generated infinite cylindric set algebras of dimension two

There are exactly seven isomorphism types of infinite one-generated diagonal-free cylindric set algebras of dimension two all of which are described in this paper. Contrast this result with the following facts from another paper by the same author: there are continuum many two-generated such algebras and continuum many one-generated ones of finite dimension at least three.Presented by J. Mycielski.     

Etude de la structure magnetique et de la transition de typr “spin-flop” de Rb2FeF5

The nature of the magnetic interactions in the chain compound Rb₂FeF₅ has been investigated using neutron diffraction and magnetic measurements under high applied fields. Rb₂FeF₅ orders antiferromagnetically at T_N = 8.0 ± 0.5 K; the magnetic structure is of the A_Z + G_X mode and the moment of the Fe³⁺ ion extrapoled to 0K is 3.5 ± 0.2 μ_B, this low value being due to zero-point spin reduction. Within a chain the Fe³⁺ ions are antiferromagnetically coupled with an exchange constant of J/k = ?8.8 K. A spin-flop behavior has been observed and interpreted on the basis of the molecular field theory. The critical field was found to be H_C = 65 kOe at 1.7 K.     

Jahn-Teller distortion in the SnH4+ ion

The extension of the Jahn-Teller distortion of the SnH₄⁺ structure is estimated from ab initio SCF CI calculations using pseudopotential atomic approximation with and without relativistic correction. These calculations show the lowest minima of SnH₄⁺ to have C_2v symmetry and are very close to the C_3v minima. The calculated photoelectron spectrum of SnH₄ is in good agreement with the experimental values.     

Dimorphisme et structure du disulfure de lanthane LaS2

The stoichiometric lanthanum disulfide LaS₂ presents a reversible phase transition at about 750°C. The α low-temperature form is monoclinic with the LaSe₂ type. All the crystals are twinned with the same twin law (100). The cell parameters are a = 8.18, b = 8.13, c = 4.03Å, γ = 90°, space group $\text{P2}{}_1\text{a}$. The β high-temperature form has the orthorhombic structure previously described with the parameters a = 8.13, b = 16.34, c = 4.14 Å; space group Pnma. The two structures are compared.     

Decatungstate (W10O)/Silane: A New and Promising Radical Source Under Soft Light Irradiation

The use of decatungstate in combination with silanes to generate silyl radicals under green fluorescence bulb irradiation as well as sunlight exposure is described. The mechanisms are investigated by ESR and laser flash photolysis experiments. The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.

     

Orienting the Demixion of a Diblock‐copolymer Using 193 nm Interferometric Lithography for the Controlled Deposition of Nanoparticles

DUV interferometric lithography and diblock copolymer self‐organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long‐range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS‐b‐MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high‐density arrays of nanoparticles with potential applications in data storage.

     

Synthesis of Clicked Imidazolium‐Containing Biosourced Copolymers and Application in Carbon Nanotube Dispersion

New polyesters incorporating a variable quantity of imidazolium rings along the backbone are synthesized by Huisgen 1,3‐dipolar cycloaddition (“click” reaction). Subsequently, the imidazolium‐grafted copolymers reveal an efficient dispersing ability toward the carbon nanotubes (CNTs) through supramolecular interactions in organic media. Interestingly, these compounds offer a simple and reliable strategy to control the quantity of dispersed CNTs as a function of imidazolium content. This approach is particularly suitable for the elaboration of biosourced and biodegradable materials based on poly(butylene succinate) with high‐performance properties.