Structural Investigation of Guest-to-Host and Ligand-Ligand Interactions in Werner Clathrates of [Ni(4-Etpy)4(NCS)2]⋅ nG Type (G = Naphthalene Derivatives). The Crystal Structure of [Ni(4-Etpy)4(NCS)2]⋅1-Methylnaphthalene

The stoichiometry and spectral properties of [Ni(4-Etpy)4(NCS)2]nG clathrates have been studied where n = 2 for G = 1-BrN (N = naphthalene), n = 1 or 2 for G = 1-MeN, and n = 0.5 for 2-MeN and 2-BrN. The complexes under study show electronic absorption spectra typical of an octahedral environment of the Ni(II) central atom. The differences found in IR spectra for the (CN) and (Ni–-NNCS) vibrations are discussed. The crystal structure of [Ni(4-Etpy)4(NCS)2]1-MeN was determined by X-ray diffraction and refined to R = 0.0586. Discrete non-centrosymmetric [Ni(4-Etpy)4(NCS)2] molecules form layers of a host structure and the space between the layers is occupied by 1-MeN. The relationship between interatomic distances in the host complex of similar clathrates are discussed.     

Thermochemical Properties of Neutral Complexes in Layer Silicates I. [Ni(4-Etpy)4(NCS)2] complex in montmorillonite and pillared montmorillonites

The stoichiometry of thermal decomposition and enthalpy and structural changes were studied for the compounds formed by penetration of [Ni(4-Etpy)4(NCS)2] (I) into Ca-montmorillonite (II) or Cr-, Zr- and Al-pillared analogues (III, IV and V, respectively). The mass fractions of complex I in II, III, IV or V are different. It was found for all studied compounds that the release of L (L=4-Etpy) is a three-step process (-2L, -1L, -1L), and differences occurred in enthalpy changes (δH in kJ per mole of I) corresponding to the individual processes. These differences and the changes in diffraction and spectral properties of the species formed after intercalation are assumed to have their roots in different intramolecular guest-host interactions in the studied compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Broom-like and flower-like heterostructures of silver molybdate through pH controlled self assembly

Silver molybdate microrods are self-assembled into micron sized, broom-like and flower-like structures. Our investigations indicate that through a simple hydrothermal process, large scale production of such structure is possible. Using ammonium molybdate and silver nitrate solutions as precursors, we were able to show that the self assembled architectures were dependent on the pH of the starting precursor material. To understand the formation and destructions of the flower-like morphology, a systematic broad range (from acidic to basic) of pH-controlled experiments were performed and its influence on the structure/microstructure of synthesized materials was investigated. Scanning electron microscopy studies revealed that the morphology and microstructure of the products varied significantly by changing pH values from 3 to 8 during mixing of the reactants. pH = 3 and 4 resulted in the self assembly of monoclinic Ag₂(Mo₂O₇) microrods into broom-like structures, whereas pH = 5 resulted into the flower-like morphology of mixed phase of monoclinic and triclinic Ag₂Mo₂O₇. We also found that increasing the pH after a certain threshold value (for example pH > 6) resulted in total collapse of the flower-like morphology. Further increase of the pH to 7 and 8 resulted, the formation of microparticles of Ag₂MoO₄. A tentative scheme based on the pH-driven evolution of the self-assembly has been given to explain the formation of the observed heterostructures. Preliminary electrical characterization of thin films of the flower-like structures rendered non-linear current–voltage (I–V) responses. We also observed a strong hysteresis in the I–V responses of the flower-like structures developed under high bias conditions.     

Anomalous behaviour of LaMnO3 with small structure distortions in magnetic phase transitions range

The magnetic field effect on conductivity and intensity of the magnetic neutron diffraction reflections as well as magnetization of lanthanum manganite with different crystal lattice distortions in the ferromagnetic-paramagnetic transitions range are investigated. It is shown that in the investigated samples near the paramagnetic-ferromagnetic transition temperature at H = 0 there exists a relatively wide transition range where the magnetic ordering occurs with a relatively small external magnetic field applied.     

Debye-Waller Factors and Elastic Constants for Beryllium Oxide at Temperatures between 10 and 720 K (I). Anisotropy of Inoic Mean-Square Displacements

The Debye-Waller factors and the mean-square dynamics displacements of the Be and O ions in beryllium oxide are obtained from X-ray diffraction powder data over the temperature range from 10 to 720 K for different crystallographic directions. The observed anisotropy of these mean-square displacements is discussed.     

Elementary components of buildup curve for F1 -centers in KCl at room temperature

The buildup kinetics of F₁ centers in KCl is studied. The dosage dependence of their densities contains two stages, a rapid stage and a slow stage. The rapid stage consists of two elementary components of the form (1-exp). The slow stage contains two linear components. A passage from the first to the second stage occurs sharply with a “deflection.” It is shown that this passage can be described by taking into account track effects.     

Growth of black holes at the centers of galaxies: Absorption of stars and activity of galactic nuclei

We study the influence of supermassive black holes on the distribution of stars at the centers of galaxies. We analyze relaxation processes associated with encounters between stars and their absorption by black holes. For an isothermal distribution of stars, we obtain the growth law and estimate the current masses of black holes. The tidal disruption of stars near black holes is considered as a possible cause of the activity of galactic nuclei.     

Singularities of angular spectral characteristics of the radiation of an electron moving along the ARC of a circle

A detailed analysis is given of the angular distribution and low-frequency domain of the radiation spectrum of an electron moving over a circular arc.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 72–76, July, 1982.