Conformational study of 2-arylazo-1-vinylpyrroles

Conformational study of 2-phenylazo-1-vinylpyrrole and 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole was performed on the basis of the experimental measurements and high-level ab initio calculations of their 13C--13C and 13C--1H spin-spin coupling constants, showing marked stereochemical behaviour upon the internal rotation of the vinyl group and the pyrrolyl moiety. In liquid phase, both compounds were found to adopt predominant s-trans-s-trans conformation with the noticeable population (ca. 30%) of the higher-energy s-cis-s-trans conformation in the latter compound. As follows from the X-ray data, 2-phenylazo-1-vinylpyrrole crystallizes in s-trans-s-trans conformation while the crystalline molecular structure of 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole is s-cis-s-trans.     

The belok station for protein crystallography on the synchrotron radiation beam from the bending magnet in the Sibir-2 storage ring

Design modifications made in the initial project of the Belok station in the Sibir-2 storage ring and the alignment and calibration methods are considered. The main operating parameters of the station are reported. Protein single crystals in a capillary at T = 293 K and without a capillary at T = 95 K, powders (angular resolution Δ2? = 0.04°), and nanocrystalline Na and Cl₂ precipitates (sizes, shape, and orientation) in electron-irradiated NaCl crystals have been investigated. The problem of focusing of a short-wavelength synchrotron radiation beam with sagittal bending of the second crystal in the double-crystal monochromator at a limited source-to-sample distance is solved in the Belok project.     

EPR observations of anomalous triplet states in Ba1−x KxBiO3 and BaPbyBi1− y O3

Electron paramagnetic resonance (EPR) spectra of samples of the systems Ba_1−x K_xBiO₃ and BaPb_yBi_1−y O₃ are investigated over wide ranges of composition and temperature. Two main lines in the EPR spectrum with factors g ₁≈2.1 and g ₂≈4.2 are found for all compositions. It is shown that the observed EPR line with g ₂≈4.2 is due to oxygen ions. This probably indicates the presence of oxygen ions with different effective charges, i.e., the existence of charge density waves in the oxygen-ion sublattice in addition to charge density waves in the bismuth sublattice. Zh. éksp. Teor. Fiz. 115, 1326–1336 (April 1999)     

Physical model of thermally induced diffusion and phase-formation processes in layered systems containing three isotopes of two elements

Previously formulated physical principles are used to develop a mathematical model of thermally induced processes of diffusion, phase formation, and stabilization of a spatially inhomogeneous structural-phase state in layered systems containing three isotopes of two elements. The program realization of the model allows quantitative characterization of the kinetics of these processes under arbitrary conditions of thermal annealing. The results of theoretical calculations and the experimental data obtained by Mössbauer spectroscopy and X-ray diffractometry of the layered structure consisting of ⁵⁷Fe (0.07 μm)-Ti (1 μm)-Fe_0.96Ti_0.04 (13 μm)-⁵⁷Fe(0.07 μm) are found to be in good agreement.     

Quadrupole interactions in tetraoxoferrates (VI)

An applicability of the point charge approach for calculations of quadrupole splittings in Mössbauer spectra of ferrates(VI) was studied. The reasonable correlation between calculated and experimental splittings was observed for the majority of ferrates excepting K₃Na(FeO₄)₂. The comparison of ferrates and chromates was made using calculated nucleus independent coefficient.     

Structural transformations in La1 − x Ba x Mn0.98 57Fe0.02O3 + δ (x = 0.05−0.20)

Physics of the Solid State - A systematic investigation of the structural transformations in La1 ? x Ba x Mn0.98 57Fe0.02O3 + δ (x = 0.05?0.20) at different Ba concentrations and...     

Fluorine spin–spin coupling constants of pentafluorobenzene revisited at the ab initio correlated levels

All possible spin–spin coupling constants, ¹⁹F–¹⁹F, ¹⁹F–¹³C, and ¹⁹F–¹H, of pentafluorobenzene were calculated at five different levels of theory, HF, DFT, SOPPA (CCSD), CCSD, and the SOPPA (CCSD)-based composite scheme with taking into account solvent, vibrational, relativistic, and correlation corrections. Most corrections were next to negligible for the long-range couplings but quite essential for the one-bond carbon–fluorine coupling constants. Hartree–Fock calculations were found to be entirely unreliable, while DFT results were comparable in accuracy with the data obtained using the wave function-based methods.     

Indirect relativistic bridge and substituent effects from the ‘heavy’ environment on the one‐bond and two‐bond 13C1H spin–spin coupling constants

Indirect relativistic bridge effect (IRBE) and indirect relativistic substituent effect (IRSE) induced by the ‘heavy’ environment of the IV‐th, V‐th and VI‐th main group elements on the one‐bond and geminal ¹³C? ¹H spin–spin coupling constants are observed, and spin‐orbit parts of these two effects were interpreted in terms of the third‐order Rayleigh–Schrödinger perturbation theory. Both effects, IRBE and IRSE, rapidly increase with the total atomic charge of the substituents at the coupled carbon. The accumulation of IRSE for geminal coupling constants is not linear with respect to the number of substituents in contrast to the one‐bond couplings where IRSE is an essentially additive quantity. Copyright © 2015 John Wiley & Sons, Ltd.     

New complex silver-scandium vanadates

New complex silver-scandium vanadates, Ag₃Sc(VO₄)₂, AgBaSc(VO₄)₂, and Ag₃Sc₂(VO₄)₃, were synthesized, and their crystallographic parameters were determined. The products synthesized by different methods were studied by X-ray powder diffraction, electron-probe X-ray microanalysis, and ESR. Based on these data, the synthetic procedures were optimized. The thermal properties of complex vanadates were studied by DTA. The compounds AgBaSc(VO₄)₂ and Ag₃Sc₂(VO₄)₃ were shown to exhibit polymorphism. The compounds Ag₃Sc(VO₄)₂, AgBaSc(VO₄)₂, and Ag₃Sc₂(VO₄)₃ decompose at 760, 780, and 960 °C. respectively.