Electronic structure and Chemical bonding in Sr4Nb17O26

The electronic structure of oxoniobate Sr₄Nb₁₇O₂₆ is studied by the linear muffintin orbital (LMTO) method. It is shown that the highenergy conduction band consists of the Nb4d states and the hybridized valence band is formed by the Nb4d and O2p states. The band structure of this compound is characterized by superposition of the bands of the 2p states of perovskite oxygen atoms and the 4d states of monoxide niobium atoms. The degree of oxidation of the perovskite and monoxide niobium atoms is +5 and +2.56, respectively. Chemical bonding is analyzed using the electron localization function and model Hückel calculations. The niobiumoxygen bond is shown to be the strongest. The Fermi level is localized in the vicinity of the bottom of the niobium antibonding state band, which explains the existence of Sr_4−xNb₁₇O₂₆ in the homogeneity region corresponding to 0 < x < 0.3. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 771–780, September–October, 1998. This work was supported by RFFR grant No. 96-03-32015a.     

Oxidation of organic sulfides with atmospheric oxygen in the presence of phthalocyanine complexes as catalysts

Catalytic oxidation of a mixture of low-molecular-weight sulfides with atmospheric oxygen was studied. The catalytic activity of poly(cobalt phthalocyanine) in this process is higher than that of monomeric cobalt phthalocyanine.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Optical properties of the Cr<Subscript>5</Subscript>S<Subscript>6</Subscript> single crystal

Results of the investigation of optical density spectra of Cr₅S₆ single crystals in the infrared region have been presented. A comparative analysis of the temperature dependences of the magnetization and the light absorption has been performed. Physical mechanisms to explain the specific features of the spectral and temperature dependences of the optical density have been proposed.     

Synthesis of (1′S*,2R*,3R*)- and (1′S*,2R*,3S*)-N-arylsulfonyl-2-(1′-halogenethyl)-3-methylindolines and their selective toxicity against SH-SY5Y cell line

N-tosyl-2- and N-tosyl-4-halogen-substituted derivatives of 2-(1-methylbut-2-en-1-yl)aniline were synthesized and their molecular iodine-mediated cyclization was investigated. The cyclization upon interaction of N-tosyl-6-methyl-2-(1-methylbut-2-en-1-yl)aniline with molecular iodine in methyl tert-butyl ether or acetonitrile was studied, as well as the interaction of this sulfonamide with N-bromosucinimide in dichloromethane. Synthesized (2R*,3R*)- and (2R*,3S*)-N-arylsulfonyl-2-(1-halogenoethyl)-3-methylindoline derivatives showed cytotoxic activity against HEK293 cells, SH-SY5Y, Jurkat, and HepG2 cell lines. The compounds (2R*,3S*)-N-arylsulfonyl-7-bromo-2-(1-halogenoethyl)-3-methylindoline cis- 4a , stereoisomeric (2R*,3R*)-trans- 4h and (2R*,3S*)-N-tosyl-7-chloro-2-(1-halogenoethyl)-3-methylindoline cis- 4h demonstrated selective toxicity against SH-SY5Y cell line (IC₅₀ ≈ 3 ÷ 5 μM), and did not affect HEK293, Jurkat, and HepG2 cells.     

Hall effect in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> crystals

A study of the temperature dependences of the ordinary and anomalous Hall coefficients and of the Hall mobility of carriers in single crystals of the ferromagnetic manganites La_1?xSr_xMnO₃ (x=0.15, 0.20, 0.25) was carried out in the temperature interval from 85 to 400 K. The nature of the carriers and the conduction mechanisms in these compounds are discussed.     

Floating zone growth and compositional inhomogeneity study of La0.75Y0.05Sr0.2MnO3 single crystals

Single crystals of La_0.75Y_0.05Sr_0.2 MnO₃ have been grown by the floating zone technique. The yttrium distribution in the radial and axial directions in the crystals was studied for different growth rates. The sample grown at high rate showed inhomogeneity in the yttrium content in the growth direction, while the sample grown at relatively low rate was homogeneous in the growth direction, but demonstrated compositional separation between the Y-poor central part and Y-enriched peripheral part in the perpendicular plane. The compositional separation led to magnetic inhomogeneity.     

Kinetic, optical, and elastic properties of La0.60Eu0.07Sr0.33MnO3

An experimental study is reported of the temperature dependences of the electrical resistivity and magnetoresistance, thermal and magnetothermal EMF, the Hall effect, optical reflectance, sound velocity, and internal friction of polycrystalline lanthanum manganite La_0.60Eu_0.07Sr_0.33MnO₃ carried out within the 77–430-K temperature range. Substitution of a small amount of europium for lanthanum has been found to result in a considerable decrease in the resistivity and a change in the behavior of its temperature dependence. Four characteristic temperatures at which special features are observed in the above properties have been identified. The discussion of the conduction mechanisms involved is based on the concept of mobility edge motion.     

Effect of doping by boron,carbon, and nitrogen atoms on the magnetic and photocatalytic properties of anatase

The effect of doping of titanium dioxide with the anatase structure by boron, carbon, and nitrogen atoms on the magnetic and optical properties and the electronic spectrum of this compound has been investigated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) band-structure method in the local spin density approximation explicitly including Coulomb correlations (LSDA + U) in combination with the semiempirical extended Hückel theory (EHT) method. The LSDA + U calculations of the electronic structure, the imaginary part of the dielectric function, the total magnetic moments, and the magnetic moments at the impurity atoms have been carried out. The diagrams of the molecular orbitals of the clusters Ti₃ X (X = B, C, N) have been calculated and the pseudo-space images of the molecular orbitals of the clusters have been constructed. The effect of doping on the nature and origin of photocatalytic activity in the visible spectral range and the specific features of the generation of ferromagnetic interactions in doped anatase have been discussed based on the analysis of the obtained data. It has been shown that, in the sequence TiO_{2 ? y} N _y → TiO_{2 ? y} C _y → TiO_{2 ? y} B _y (y = 1/16), the photocatalytic activity can increase with the generation of electronic excitations with the participation of impurity bands. The calculated magnetic moments for boron and nitrogen atoms are equal to 1 μ_B, whereas the impurity carbon atoms are nonmagnetic.     

The effect of crystal lattice distortions on the electronic band structure and optical properties of the N,V- and N,Na-doped anatase

The crystal structure, energy band structure and optical absorption of the N,V-doped and N,Na-doped anatase are studied by means of the first-principle pseudo-potential plane wave and linear muffin-tin orbitals methods. We show that the nitrogen and vanadium atoms have a tendency to form covalently bonded pairs. The crystal lattice distortions associated with doping essentially affect the optical absorption. With doping the impurity bands emerge in the band gap of the host anatase, however, a noticeable increase of optical absorption takes place at the energy only above 3 eV. Possible impact of this effect on the photocatalytic activity of the doped anatase is outlined.