Vladimir V. Chernyshev

MRIA ‐ a program for a full profile analysis of powder multiphase neutron‐diffraction time‐of‐flight (direct and Fourier) spectra

The paper describes a universal program MRIA for the full profile analysis of powder neutron-diffraction time-of-flight direct and Fourier spectra. The minimum configuration of MRIA, analysing up to four spectra, four phases, 500 Miller indices for every phase and 100 independent atoms, can run on an IBM PC-AT or any compatible. The extended variant of the program, analysing data of larger size, runs on a MicroVAX computer. Part of MRIA, providing necessary service functions for a PC user, is written in TurboPascal 6.0. The basic programs of MRIA are written in standard Fortran77 and can be compiled by RMFORT or MSFORT77 and by an NDP compiler on a 32 bit PC.

Structure determination from powder diffraction

The review surveys modern methods for the determination of unknown crystal structures of organic and inorganic compounds from powder diffraction data. The main stages of this process, from the preparation of the specimen to a search for the structural motif followed by the Rietveld refinement, are considered. The results obtained on different diffractometers using X-ray, synchrotron, and neutron radiations are demonstrated to be well reproducible. Examples of successful structure solution are cited, which provide evidence that powder diffraction is a reliable tool in establishing structures of a wide range of compounds for which single crystals are unavailable.

Application of simulated annealing approach for structure solution of molecular crystals from X-ray laboratory powder data

Abstract Simulated annealing approach was successfully applied to solve three unknown molecular structures from X-ray laboratory powder data using a priory known structural fragments. Some possible developments of the method are discussed.

Structural study of lanthanum oxysulfate (LaO)2SO4

Abstract The structure of lanthanum oxysulfate (LaO) 2 SO 4 was studied with neutron, electron, and X-ray diffraction using the Rietveld refinement method. The unit cell is determined to be monoclinic ( a = 14.349(1), b = 4.2852(5), c = 8.386(1) A , β = 107.00(1), Sp.gr. C2 c ). The structure is similar to that of grandreefite and consists of the alternative sulfate and (LaO) layers. Every sulfate oxygen is coordinated with two lanthanum atoms. The experimental data were confirmed by the energy minimization calculations.

Synthesis of Asymmetric Peroxides: Transition Metal (Cu, Fe, Mn, Co) Catalyzed Peroxidation of β-Dicarbonyl Compounds with tert-Butyl Hydroperoxide

The transition metal (Cu, Fe, Mn, Co) catalyzed peroxidation of beta-dicarbonyl compounds at the alpha position by tert-butyl hydroperoxide was discovered. A selective, experimentally convenient, and gram-scale method was developed for the synthesis of alpha-peroxidated derivatives of beta-diketones, beta-keto esters, and diethyl malonate. Virtually stoichiometric (2-3/1) molar ratios of tert-butyl hydroperoxide and a dicarbonyl compound were used in the reactions with beta-diketones and beta-keto esters. The target compounds were synthesized in the highest yields from beta-keto esters (45-90%) and in somewhat lower yields from beta-diketones (46-75%) and malonates (37-67%).

Facile and Selective Procedure for the Synthesis of Bridged 1,2,4,5-Tetraoxanes; Strong Acids As Cosolvents and Catalysts for Addition of Hydrogen Peroxide to β-Diketones

A facile, experimentally simple, and selective method was developed for the synthesis of bridged 1,2,4,5-tetraoxanes based on the reaction of hydrogen peroxide with beta-diketones catalyzed by strong acids (H(2)SO(4), HClO(4), HBF(4), or BF(3)). The yields of the target products vary from 44% to 77%. 1,2,4,5-Tetraoxanes can easily be separated from other reaction products by column chromatography. A high concentration of a strong acid is a key factor determining the selectivity of formation and the yield of 1,2,4,5-tetraoxanes. Unlike many compounds containing the O-O bond, which undergo rearrangements in acidic media, the resulting cyclic peroxides are quite stable under these conditions.

Structure analysis of the cubic boron nitride crystals

Abstract Cubic BN crystals grown in different growth systems were studied by X-ray diffraction, IR and EPR spectroscopy methods. The unit cell parameters of the crystals and the thermal vibrations of B and N sublattices were determined.

Acemetacin cocrystals and salts: structure solution from powder X-ray data and form selection of the piperazine salt

Multi-component crystals of the anti-inflammatory drug acemetacin were prepared by melt crystallization and their X-ray crystal structures solved using single-crystal and high-resolution powder X-ray diffraction (PXRD) data. The acemetacin–para-aminobenzoic acid adduct and the acemetacin piperazine salt are stable to hydration in the aqueous medium (up to 24 h).

Selective Synthesis of Cyclic Peroxides from Triketones and H2O2

A method for the assembly of tricyclic structures containing the peroxide, monoperoxyacetal, and acetal moieties was developed based on the acid-catalyzed reaction of β,δ-triketones with H(2)O(2). Tricyclic compounds are formed selectively in yields from 39% to 90% by the reactions with the use of large amounts of strong acids, such as H(2)SO(4), HClO(4), or HBF(4), which act both as the catalyst and as the co-solvent. The reaction is unusual in that, despite the diversity of possible peroxidation pathways giving cyclic compounds and oligomers, the reaction proceeds with high selectivity and produces tricyclic peroxides via the monoperoxidation of the carbonyl groups in the β-positions and the transformation of the δ-carbonyl group into the acetal one. The syntheses are scaled up to tens of grams, and the resulting peroxides can be easily isolated from the reaction mixture.

X-ray analysis and computer modeling of the structure of 'relaxor' ferroelectrics Pb3MgNb2O9 and Pb2ScTaO6 in the paraelectric state

A structural study of Pb3MgNb2O9 and ordered Pb2ScTaO6 single crystals is made by X-ray diffraction at high temperatures. Displacements of the Pb atom from the special site are clearly observed. Disordered atomic positions are uniformly distributed over a sphere with radius 0.2–0.3 A and with center at the special position. These atomic displacements are probably caused by local fields due to random statistical distribution of the (Mg, Nb) atoms in Pb3MgNb2O9 and, partially, the (Sc, Ta) atoms in Pb2ScTaO6. Computer modeling, based on the total-energy-minimization method, gives satisfactory agreement with experimental results.