Four-Center Nodes: Supramolecular Synthons Based on Cyclic Halogen Bonding

The isocyanide trans-[PdBr₂(CNC₆H₄-4-X′)₂] (X′=Br, I) and nitrile trans-[PtX₂(NCC₆H₄-4-X′)₂] (X/X′=Cl/Cl, Cl/Br, Br/Cl, Br/Br) complexes exhibit similar structural motif in the solid state, which is determined by hitherto unreported four-center nodes formed by cyclic halogen bonding. Each node is built up by four Type II C−X′⋅⋅⋅X−M halogen-bonding contacts and include one Type I M−X⋅⋅⋅X−M interaction, thus giving the rhombic-like structure. These nodes serve as supramolecular synthons to form 2D layers or double chains of molecules linked by a halogen bond. Results of DFT calculations indicate that all contacts within the nodes are typical noncovalent interactions with the estimated strengths in the range 0.6–2.9 kcal mol⁻¹.     

Formation of Mesopores in USY Zeolites: A Case Revisited

Steaming of NH₄Y zeolite at 723 K and 873 K is accompanied by the formation of extra‐framework amorphous aluminosilicate and silica gel in addition to earlier observed extra‐framework aluminum species. Their occurrence is directly associated with the formation of mesopores. Bulk (intracrystalline) mesopores occur inside the crystallite nuclei and surface (intercrystalline) mesopores are located nearby the crystallite surface. Corrosion of the zeolite framework results in a loss of crystallinity and, consequently, decreased catalytic activity of the USY catalysts synthesized. Analysis of the reasons of mesopore formation may help to reduce these disadvantages.     

Physicochemical and Catalytic Properties of La1 – xCaxFeO3 – 0.5x Perovskites Prepared Using Mechanochemical Activation

The phase composition of La_{1 – x} Ca _x FeO_{3 – 0.5x} perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900° for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 ° decreased the calcium content of the samples down to x 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.     

Conjugate Elimination of Fluorine Atoms in Halophosphonates

Facile electrochemical elimination of fluorine on a mercury drop electrode in aqueous-ethanol solutions on the background of 0.1 M Bu₄NBF₄ (E _{1 / 2} 2.0 V against saturated calomel electrode) from diethyl chlorofluoromethyl- and diethyl dichlorofluoromethylphosphonates was observed. Under the same conditions, diethyl fluoromethylphosphonate is not reduced.     

Structural study of titanium doped vanadia and vanadium doped titania catalysts

The morphologies and structures of nanostructurally assembled V₂O₅ doped with Ti as well as of the inverse system, V-doped TiO₂, have been studied using transmission electron microscopy and Raman spectroscopy. The bulk structure of the Ti-doped vanadia particles was found to be crystallized in a rod-like shape and to have the phase composition of V₂O₅ with titanium atoms nonuniformly distributed over the surface. A coherent interface between supported V₂O₅ and TiO₂ particles was found to be the main structural peculiarity of the inverse system, V-doped TiO₂ (anatase). The vanadium atoms are partially exchanged for titanium atoms at the interface, which leads to a change in the bond lengths of V=O and V-O-Ti in comparison with those observed in the monolayer supported vanadia catalysts. Both materials showed good catalytic behavior in the reaction of selective reduction of NO by NH₃. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mirror Magnetic Field and Its Impact on Dark Matter Distribution in Galaxies

Journal of Experimental and Theoretical Physics - We obtain the value of the mirror magnetic field during different stages of cosmological evolution. We consider the magnetic field generation in...     

Combined Scheme of Reconstruction of the Particle Size Distribution Function Using Small-Angle Scattering Data

JETP Letters - To analyze polydisperse systems of nanoparticles, the particle size distribution function can be determined from small-angle X-ray and neutron scattering data using some algorithms....     

Bleaching of buckwheat straw and peel with potassium peroxoborate

The use of potassium peroxoborate for bleaching buckwheat production waste, straw and peal, both untreated and treated with water, mineral acids, sodium hydroxide, and organic solvents, is examined.     

Physicochemical and catalytic properties of La1-xCax FeO3-0.5x perovskites

The phase analysis of La_1-xCa_xFeO_3-0.5x perovskites prepared by a ceramic process from oxides is studied by X-ray diffraction and differential dissolution methods. Atx < 0.5, the system does not form a continuous series of homogeneous solid solutions and does not consist of the members of a homological series. Atx < 0.5, the system contains two phases and calcium ferrite nanoparticles located on the surface of lanthanum ferrite. Atx > 0.5, the formation of the structures of a brownmillerite-based homological series is found. The catalytic activity of perovskites depends nonmonotonically on thex value and reaches the maximum atx = 0.6.