High-temperature redistribution of cation vacancies and irreversible magnetic transitions in the Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S nanodisks observed by the Mössbauer spectroscopy and magnetic measurements

The hexagonal pyrrhotite Fe_1?x S nanodisks with the NiAs-type structure were synthesized by thermal decomposition of ferrous chloride and thiourea in oleylamine. The Mössbauer spectroscopy and magnetic measurements data indicate that a mixture of antiferromagnetic (AFM) and ferrimagnetic (FRM) phases with the NC (N ≥ 3) and 2C-type superstructures is present in the Fe_1?x S compound at temperatures between 80 K and Néel temperature T _N. At T < 370 K, the AFM phase prevails over the FRM phase. At T > 370 K, a redistribution of iron vacancies takes place, and the vacancy ordering transforms from the NC (N ≥ 3) to 2C-type which essentially increases the magnetization with maximum value at 470 K. Heating the sample above the Néel temperature 565 K leads to a random distribution of vacancies, and this state is quenched upon subsequent cooling of the sample to 300 K. This gives rise to a pure AFM structure with a zero magnetic moment due to a total compensation of the moments in neighboring iron layers. Thus, the high-temperature redistribution of cation vacancies leads to irreversible magnetic transformations in the Fe_1?x S nanoparticles.     

Kinetics and mechanism of the growth of gold nanoparticles by reduction of tetrachloroauric acid by hydrazine in Triton N-42 reverse micelles

The kinetics of the growth of gold nanoparticles during the reduction of tetrachloroauric acid by hydrazine in dispersed aqueous solution encapsulated by reverse micelles of Triton N-42 surfactant (with decane as dispersion medium) was studied by means of spectrophotometry. According to DLS data, at a set value of solubilization capacity V _s/V _o = 0.005 initial micelles have an aqueous core hydrodynamic diameter d _c = 3.6±0.2 nm. The final particles obtained after full reduction of Au^III have a metallic core of defect-free single-crystalline gold with a narrow size distribution and average core diameter d _Au = 7.7 ± 1.4 nm as shown by TEM. The rate of the particle growth is limited by the rate of gold reduction. The process kinetics corresponds to the model consisting of two stages of reduction Au^III → Au^I → Au⁰. The stages involve the formation and redox decay of the intermediate complexes Au(N₂H₄)Cl₃ and Au(N₂H₄)Cl, and each stage proceeds via two routes: (1) homogeneous in the dispersed aqueous phase, and (2) heterogeneous on the particle surfaces. Reactions taking route (2) are autocatalytic because they proceed with participation of the surface atoms of particles as the final products of Au^III reduction. The dependencies of observed rate constants on reagent concentrations, temperature, and solubilization capacity of the micellar solution are studied.     

Developing Bicatalytic Cascade Reactions: Ruthenium-catalyzed Hydrogen Generation From Methanol

A novel state-of-the-art bicatalytic system for hydrogen generation from aqueous methanol at low temperature and base concentration is described. Applying two molecularly defined ruthenium complexes A and B3 for methanol dehydrogenation at the same time under the same conditions, a synergistic effect is observed. This behavior is explained by the increase of the dehydrogenation of formic acid, which is formed as an intermediate, by the second catalyst B3 .     

Halo-heterocyclization of trans-5-phenyl-3-cinnamylsulfanyl[1,2,4]triazine into [1,3]thiazino[3,2-b][1,2,4]triazin-9-ium systems

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A Titanium Metal–Organic Framework with Visible-Light-Responsive Photocatalytic Activity

The one-step synthesis and characterization of a new and robust titanium-based metal–organic framework, ACM-1 , is reported. In this structure, which is based on infinite Ti−O chains and 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl) tetrabenzoic acid as a photosensitizer ligand, the combination of highly mobile photogenerated electrons and a strong hole localization at the organic linker results in large charge-separation lifetimes. The suitable energies for band gap and conduction band minimum (CBM) offer great potential for a wide range of photocatalytic reactions, from hydrogen evolution to the selective oxidation of organic substrates.     

Sorbent for the separation of enantiomers of amino acids based on silica gel modified with stabilized Au nanoparticles

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Synthesis and biological activity of 3,5-diacetyl-2,6-dimethylpyridine derivatives

Chemistry of Heterocyclic Compounds - Aldol-crotonic condensation reactions of 3,5-diacetyl-2,6-dimethylpyridine with various aldehydes were used to synthesize bisazachalcone derivatives, which...     

Unexpected formation of novel two-component gels comprising of glycoluril carboxylic acid amides and imidazole: Synthesis and morphology

New gelling agents have been discovered: glycoluril carboxylic acid amides, giving two-component gels with imidazole. First, the one-pot, two step reaction of glycoluril carboxylic acids, CDI and various amines was investigated for the preparation of gels and it was found that the reaction mixtures were gelled in dry DMF during the preparation of some amides. The conditions of the gel-sol-gel transitions were found. The morphology of the xerogels was studied by SEM. The structure of the xerogels is constructed from interlocked rods or from interlaced curved fibres. Self-organization in the co-crystals of amides with H₂O or imidazole was detected. The molecules of the co-crystals of amides with H₂O are self-assembled into homochiral tapes.