Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

Single‐crystal X‐ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid‐state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical‐atom least‐squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld‐atom refinement (Acta Crystallogr. Sect. A­ 2008 , 64, 383–393; IUCrJ. 2014 , 1,61–79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B­ 2013 , 69, 91–104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear‐coordinate 3d metal complexes, for which the wrong element is found if standard independent‐atom model scattering factors are relied upon, are studied, and it is shown that only aspherical‐atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.     

Thiol‐Directed Synthesis of Highly Fluorescent Gold Clusters and Their Conversion into Stable Imaging Nanoprobes

Fluorescent gold clusters (FGCs) with tunable emission from blue to red and quantum yields in the range of 6–17 % have been synthesized by simple modification of the conditions used for the synthesis of gold nanoparticles, namely by replacing the stronger reducing agent with a controlled amount of thiol. Various functional FGCs with hydrodynamic diameters of 5–12 nm have been successfully synthesized and used as cell labels. The results of our investigations strongly indicate that FGCs composed of Au⁰ are more stable imaging probes than commonly reported red/NIR‐emitting FGCs with a composition of Au⁰/Au^I, as this combination rapidly transforms into nonfluorescent large clusters on exposure to light. The FGC‐based nanoprobes reported herein exhibit stable fluorescence upon continuous light exposure and can be used as imaging probes with low cytotoxicity.     

The stability of wide high-temperature superconducting films with varying transport current

The current-carrying capacity of a wide high-temperature superconducting film under conditions of rapid injection of current is investigated theoretically. An analytic expression is derived for the rate of current injection into the film at which a marked degradation of the current-carrying capacity of the film occurs. The obtained results may be important from the standpoint of analyzing the stability of superconducting ac devices.     

Synthesis and extraction properties of oxathiacrown compounds containing benzyl groups

8-Benzyl-1.4-dioxa-7,10-dithiacyclododecane and 11-benzyl-1,4,7-trioxa-10,13-dithiacyclopentadecane were obtained by the interaction of (2,3-dibromo-1-propyl)benzene with 1,8-dimercapto-3,6-dioxaoctane and 1,11-dimercapto-3,6,9-trioxaundecane. The extracting ability of the obtained compounds has been studied in relation to Sr²⁺ and Pb²⁺ ions from aqueous solutions in the presence of anions of various degrees of hardness with determination of the metal content by a radiometric method. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 244–249, February, 2006.     

Convection in an oscillating force field and microgravity

Convective flows in a plane layer of viscous fluid in the presence of an oscillating external force are investigated numerically [1 – 8]. The layer is assumed to be placed in a gravitational field. The cases in which the external field oscillations are generated by rotation about the horizontal axis or by vibration in the longitudinal direction are considered. The Navier-Stokes equations and the Boussinesq approximation are used for describing the fluid motion. The flows developing in the layer in the presence of a transverse temperature gradient are determined, the stability boundaries of these flows are found, and the supercritical motion regimes are studied. These investigations are carried out using the averaging method (in order to find the stability limits for high rotation velocities and vibration frequencies) and the Galerkin method.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 99–106, September–October, 1994.     

Investigation of the structural aspects in the formation of optical properties of the GeO2-Eu2O3-Ag nanosystem

The structural characteristics of the 95GeO₂-5Eu₂O₃, 94.9GeO₂-5Eu₂O₃-0.1Ag, and 99.9GeO₂-0.1Ag xerogels annealed in air at the temperature T _an = 850°C have been studied using X-ray diffraction and small-angle neutron scattering. It has been established that the significant change in the relative intensity of the ⁷ F ₀ → ⁵ L ₆ and ⁷ F ₀ → ⁵ H ₆ luminescence excitation bands of Eu³⁺ ions upon introduction of silver correlates with the decrease in the characteristic sizes of polydisperse clusters formed during annealing. The character of the changes in chemical bonds in the system due to the clustering and their role in the formation of optical properties have been analyzed.     

Niobium (V) peroxocomplexes as a catalyst of oxidation of methylphenylsulphide by hydroperoxide

The electrospray ionization-mass spectrometry (ESI-MS) method has been used for determination of the structure of niobium peroxocomplexes. The formation of mono- and bisperoxocomplexes has been established. These complexes contain Schiff bases and 8-quinolinol as ligands. Trisperoxocomplexes are formed when pyridine and 1,10-phenanthroline are used. Peroxocomplexes with Schiff bases as ligands has shown a high activity as catalysts in the methylphenylsulphide oxidation.     

Facile Transformation of the Hydroxy‐Substituted Oxathiacrown Ethers

9(12)‐Hydroxy‐dithia‐13(16)‐crown‐4(6)‐ethers have been prepared by the condensing an oligoethylene glycol dithiol with 2,3‐dibromo‐1‐propanol. Methods of oxidation, halogenation, amination, and esterification of the 9‐hydroxythiacrown ether, producing corresponding oxathiacrown ether derivatives in good yields, have been developed. Cyclic destruction has not been found in the studied reactions. The change of the oxathiamacrocyclic ring size in the course of the halogenation and amination reactions was revealed.     

Tunneling magnetoresistance of phase-separated manganites

A simple model of phase separation is used to study the magnetoresistance of manganites in the nonmetallic state. It is assumed that the phase separation corresponds to the emergence of small ferromagnetic metallic droplets (ferrons) in a nonconducting antiferromagnetic or paramagnetic medium, with the metallic phase concentration being far from the percolation threshold. The charge transfer is accomplished by way of electron jumps between droplets. The magnetoresistance in such a system is defined both by the variation of the volume of the metal phase and by the dependence of the probabilities of electron transitions on the magnitude of the magnetic field. It is demonstrated that, in the region of low magnetic fields, the magnetoresistance is quadratic with respect to the field and decreases with temperature by the T ^?n law, where n takes values from 1 to 5 depending on the correlation between the parameters. In the high-field limit, the magnetoresistance increases abruptly with the volume of the metal phase. The crossover of the field dependence from quadratic to a stronger one may be accompanied by the emergence of a platean in the magnetoresistance. The correlation between the obtained results and the available experimental data is discussed.