Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations

Pressure-induced insulator-to-metal transition (IMT) has been studied in the van der Waals compound iron thiophosphate (FePS₃) using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid Hartree–Fock-DFT B3LYP functional. Our calculations reproduce correctly the IMT at ∼15 GPa, which is accompanied by a reduction of the unit cell volume and of the vdW gap. We found from the detailed analysis of the projected density of states that the 3p states of phosphorus atoms contribute significantly at the bottom of the conduction band. As a result, the collapse of the band gap occurs due to changes in the electronic structure of FePS₃ induced by relative displacements of phosphorus or sulfur atoms along the c-axis direction under pressure.     

Crystal Structure of Synthetic High-Chromium Analogue of Yimengite

Crystallography Reports - The structure of a potassium compound with the chemical formula K0.90Ti5.16Cr2.94Fe2.54Mg0.87Al0.22Mn0.30O19 has been investigated by single-crystal X-ray diffraction...     

Determination of temperature in a plasma jet emanating from a plasma torch with sectioned inter-electrode insert from the molecular emission spectrum of nitrogen

Results of application of a method for measuring the distribution of temperature in a nitrogen plasma jet emanating from a dc plasma torch with sectioned inter-electrode insert from the relative intensities of the molecular emission bands of nitrogen in the N₂ ⁺(B²Σ_u ⁺ − X²Σ_g ⁺) first negative and N₂(C³Π_u ⁺ − B³Π_g ⁺) second positive systems are reported. The emission spectra were registered using a small-size spectrometer with medium-range spectral resolution enabling a contour analysis of ro-vibrational bands in molecular emission spectra. The obtained distribution of temperature was compared with the distribution that was determined from the emission lines due to copper atoms and with the mean-mass plasma temperature of the air plasma jet.     

Superbase‐catalyzed domino 3H‐pyrroles synthesis from ketoximes and acetylene: DFT study vs experiment

Elimination of vinyl alcohol from 5‐vinyloxypyrrolines in the presence of superbases (final step of domino 3H‐pyrroles synthesis from ketoximes and acetylene) is studied computationally at different levels of theory in DMSO solution (PCM). The sequences of transformations starting from nucleophilic addition of hydroxide ion to carbon‐carbon or carbon‐nitrogen double bonds are proposed as possible mechanisms. Unusual reactivity of 2,5‐dimethylphenyl substituted 5‐vinyloxypyrroline is explained within these mechanisms.     

Redox Activation of Hydrogen Sulfide,Thiols, and Sulfur in Electrosynthesis of Organic Di- and Polysulfides

Russian Journal of General Chemistry - A novel and efficient method for the synthesis of biologically active organic di-, tri- and tetrasulfides has been proposed. Different methods of redox...     

Decacyclene Radical Anions Showing Strong Low‐energy Intramolecular Absorption and Magnetic Coupling of Spins in a Hexagonal Network

Two salts of the aromatic hydrocarbon decacyclene, {cryptand[2.2.2](Cs⁺)} (decacyclene^.?) ( 1 ) and {Bu₃MeP⁺}(decacyclene^.?) ( 2 ), were obtained. In both salts, decacyclene^.? radical anions formed channels occupied by cations. However, corrugated hexagonal decacyclene^.? layers could be outlined in the crystal structure of 1 with several side‐by‐side C???C approaches. The decacyclene^.? radical anions showed strong distortion in both salts, deviating from the C₃ symmetry owing to the repulsion of closely arranged hydrogen atoms and the Jahn‐Teller effect. Radical anions showed intense unusually low energy absorption in the IR‐range, with maxima at 4800 and 6000 cm^?1. According to the carculations, these bands can originate from the SOMO‐LUMO+1 and SOMO‐LUMO+2 transitions, respectively. Radical anions exhibited a S=1/2 spin state, with an effective magnetic moment of 1.72 μ_B at 300 K. The decacyclene^.? spin antiferromagnetically coupled with a Weiss temperature of ?11 K. Spin ordering was not observed down to 1.9 K owing to spin frustration in the hexagonal decacyclene^.? layers.     

Magnetism in disordered magnetic Fe82−xNixCr18

The zero field μSR-method has been used to study the magnetism in the disordered magnetic alloy Fe_82−xNi_xCr₁₈ near the three-critical, pointx=25. The dynamic and static local field distributions are analyzed. The difference between spin-glass states obtained either from the paramagnetic or after the double transition is discussed.     

Raman and photoluminescence spectroscopy of zinc tungstate powders

ZnWO₄ powders, synthesized using co-precipitation technique and annealed in air at different temperatures in the range of 80-, were studied by Raman and photoluminescence spectroscopy. ZnWO₄ single crystal was used for comparison. The interpretation of the observed variations of the Raman spectra and intrinsic photoluminescence band upon annealing is suggested.     

Investigation of coal fired combined-cycle cogeneration plants for power, heat, syngas, and hydrogen

The methodology for determination of technical and economic efficiency of coal fired combined-cycle cogeneration plant (CCCP) with low-pressure steam-gas generator and continuous flow gasifier at combined production of power, heat, syngas, and hydrogen is considered. The results of investigation are presented. Such CCCP have higher technical and economic efficiency than the pulverized coal cogeneration plant modified by gas-turbine.     

Computational study of singlet and triplet sulfonylnitrenes insertion into 1,3‐butadienes: 1,2‐ or 1,4‐cycloaddition?

The formation of N‐trifluoromethylsulfonyl‐2‐vinylaziridine and N‐trifluoromethylsulfonyl‐3‐pyrroline by the reaction of the singlet and triplet trifluoromethanesulfonylnitrenes with s‐cis‐ and s‐trans‐1,3‐butadienes was studied theoretically at the B3LYP/6‐311++G(d,p) and M06‐2X/6‐311++G(d,p) levels of theory. The singlet trifluoromethanesulfonylnitrene adds to s‐cis‐ and s‐trans‐1,3‐butadiene exothermally in one step to give the product of 1,2‐cycloaddition, N‐trifluoromethylsulfonyl‐2‐vinylaziridine, the energy decreasing by 88.5 and 86.2 kcal/mol at the B3LYP level and by 105.2 and 103.0 kcal/mol at the M06‐2X level, respectively. The formed 2‐vinylaziridine can undergo rotation about the C(2)–C_sp2 bond with the barrier not exceeding 3.5 kcal/mol and to rearrange into N‐trifluoromethylsulfonyl‐3‐pyrroline. The triplet trifluoromethanesulfonylnitrene reacts with s‐cis‐ and s‐trans‐1,3‐butadiene in two steps. The first exothermic step is the formation of the triplet diradical adducts. The second step is the spin inversion with the energy raising by 5.8 and 17.8 kcal/mol at the B3LYP level and by 11.0 and 20.8 kcal/mol at the M06‐2X level for the adducts to s‐cis‐ and s‐trans‐1,3‐butadiene, respectively. Recombination of the radical centers occurs selectively to give N‐trifluoromethylsulfonyl‐2‐vinylaziridine that is exothermally rearranged into N‐trifluoromethylsulfonyl‐3‐pyrroline with the energy barrier of 40 kcal/mol at the B3LYP level and of 50 kcal/mol at the M06‐2X level. Copyright © 2014 John Wiley & Sons, Ltd.