Kinetics of oxidation of pentaammine-isothiocyanato-cobalt(III) ion with peroxodisulphate and periodate in water and water-organic mixtures

Summary The kinetics of oxidation of [Co(NH₃)₅(NCS)]²⁺ by peroxodisulphate and periodate were investigated at different ionic strengths, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported in mixed water-organic solvents. It was shown that the acid-base equilibria involving S₂O ₈ ⁻² , and IO ₄ ⁻ ions are important in the reactions studied. Solvent effects on the oxidation are interpreted in terms of the solvation of both the initial state and the activated complex.     

Models of (ZrO2)n complexes intercalated into montmorillonite

The article discusses the properties of several model zirconium dioxide complexes (ZrO(2))(n)() intercalated into the interlayer space of montmorillonite clay. Grand canonical Monte Carlo simulation was used in a series of numerical experiments during analysis of the low-temperature nitrogen adsorption in the micropores thus generated. The goal of such experiments was to determine the geometrical parameters of introduced molecular complexes of different types inside micropores of various widths. The obtained information was used to characterize textural and structural properties of three pillared interlayer materials prepared by using pillaring species synthesized via aging of zirconyl chloride solutions containing as additives chlorides of Ca, Sr, or Ba. It was found that in the cases of Ba and Ca the interlayer micropores are filled with isolated tetramers (ZrO(2))(4). Meanwhile, the presence of Sr in the pillaring solution, most likely, favors the preservation of larger sheetlike complexes (ZrO(2))(8).     

BF3·OEt2-promoted reaction of isocyanides with o-aminobenzophenones

Aliphatic isocyanides react with o-aminobenzophenones in dichloromethane under Lewis acid catalysis at ambient temperature to give, unexpectedly, 4-aryl-4-hydroxy-3,4-dihydroquinazolines in good to excellent yields. The outcome of the reaction is rationalized by a skeletal rearrangement of the initially formed ‘intramolecular Passerini’ reaction products, 2-amino-3-hydroxy-3-aryl-3H-indoles.     

Air-oxidized products of multi-component reactions between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles

The Groebke-type multi-component reaction (MCR) between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles has been studied from the viewpoint of convenient generation of combinatorial arrays of imidazo[1,2-b][1,2,4]triazoles. However, it was established that the desired heterocyclic structures can be produced in moderate to good yields in an oxidized form, when benzylic isonitriles are used. Oxidation occurred at the benzylic position to produce N-alkylidene-4H-imidazo[1,2-b][1,2,4]triazol-6-amines that proved to be unusually stable towards acid hydrolysis and reduction. The presence of an easily oxidized benzylic position in the target structures is thought to be the prerequisite for successful Groebke-type MCR of 3-amino-1,2,4-triazole.     

Synthesis of sulfolanopyranochromenones by the reaction of 2-benzylidene-3-methyl-4-nitro-2,5-dihydrothiophene 1,1-dioxides with 4-hydroxycoumarin

Chemistry of Heterocyclic Compounds - A number of tetracyclic compounds with annulated nitrosulfolane and pyranochromenone rings were synthesized by reacting...     

Sulfur- and Selenium-Containing Compounds Potentially Exhibiting Al Ion Conductivity

We have created a set of crystalline model structures exhibiting straight lines of Al³⁺ connected to chalcogenides (O²⁻, S²⁻, and Se²⁻) connected to metal cations of varying valence (Sr²⁺, Y³⁺, Zr⁴⁺, Nb⁵⁺, and Mo⁶⁺). They were relaxed with density functional theory computations and analysed by Bader partitioning. As Al³⁺ ions are supposed to strongly interact with their atomic environment, we studied the electron density topology induced by higher-valent cations in the extended chemical neighbourhood of Al. In fact, we found a general decrease of ionic charges and an increasing displacement of the chalcogenides towards higher-valent ions for the heavier chalcogens. Therefore, we comprehensively screened S- and Se-containing compounds for candidates theoretically exhibiting low migration barriers for Al³⁺ ions by using Voronoi–Dirichlet partitioning and bond valence site energy calculations. The basis for this search is the Inorganic Crystal Structure Database. Indeed, we could extract six promising candidates with low Al³⁺ migration barriers. which are even lower than the barriers for any other element inside of these materials. This will encourage efforts towards preparing suitable Al³⁺ conductors.     

Deterministic Guarantees for Burer-Monteiro Factorizations of Smooth Semidefinite Programs

We consider semidefinite programs (SDPs) with equality constraints. The variable to be optimized is a positive semidefinite matrix X of size n. Following the Burer-Monteiro approach, we optimize a factor Y of size n × p instead, such that X = YY^T. This ensures positive semidefiniteness at no cost and can reduce the dimension of the problem if p is small, but results in a nonconvex optimization problem with a quadratic cost function and quadratic equality constraints in Y. In this paper, we show that if the set of constraints on Y regularly defines a smooth manifold, then, despite nonconvexity, first- and second-order necessary optimality conditions are also sufficient, provided p is large enough. For smaller values of p, we show a similar result holds for almost all (linear) cost functions. Under those conditions, a global optimum Y maps to a global optimum X = YY^T of the SDP. We deduce old and new consequences for SDP relaxations of the generalized eigenvector problem, the trust-region subproblem, and quadratic optimization over several spheres, as well as for the Max-Cut and Orthogonal-Cut SDPs, which are common relaxations in stochastic block modeling and synchronization of rotations. © 2019 Wiley Periodicals, Inc.     

Effects of the photocathode non-uniformity on radon measurements by plastic scintillation spectrometry

Journal of Radioanalytical and Nuclear Chemistry - This work shows a study of the effect of the non-uniformity of photocathode response on the energy resolution of plastic scintillators optimized...     

Spin Transport over Huge Distances in a Magnetized 2D Electron System

Experimental results on the properties of a recently discovered new collective state, the magnetofermionic condensate, are summarized herein. Condensation occurs in a fermionic system, a quantum Hall insulator (filling factor ν = 2), as a result of the formation of a dense ensemble of long‐lived spin cyclotron magnetoexcitons, composite bosons. At temperatures below 1 K, the exciton ensemble exhibits a sharp enhancement in its response to an external electromagnetic field due to the formation of a super‐absorbing state that interacts coherently with the electromagnetic field. Simultaneously, the electrons below the Fermi level rearrange to form a new non‐equilibrium radiative recombination channel. The condensate shows a sharp decrease in viscosity and the ability to spread over macroscopically large distances, on the order of a millimeter, at a speed of $\approx {10}^3\text{cm}{\text{s}}^{?1}$. Due to this rapid long‐distance spin transfer, new opportunities in the field of spintronics have been opened up.