C-PhosphorylatedN 2-2-thiazolylformamidines

C-Phosphorylation of 2-thiazolylformamidines by phosphorus tribromide was studied. It was shown that the 1,3-diazabut-1-enyl (formamidine) substituent can be used as both an activating and protective group. 5-Phosphorylated thiazoles containing either a formamidine fragment or an amino group were obtained. Some properties of the compounds synthesized were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1353–1359, July, 1999.     

Some aspects of reflection crystal optics

The general case of light reflection from a crystal of arbitrary symmetry in the weak anisotropy approximation has been considered. The dependence of the components of reflection matrix for a crystal with an arbitrary dielectric tensor is obtained for the case of small anisotropic corrections. The measurement of the reflection matrix components and the possibilities of subsequently determining the dielectric tensor components in measurements at different crystal orientations with the application of an ellipsometric experiment are analyzed. It is shown how the method proposed can be used to determine the characteristics of uniaxial and biaxial crystals at an arbitrary orientation of optical axes.     

Arenesulfenylation of 1,3-azoles with renesulfenyl chlorides

Institute of Organic Chemistry, Ukrainian Academy of Sciences, Kiev 252094. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1292–1293, September, 1994. Original article submitted August 5, 1994.     

“Nonmagnetic” (antiferromagnetic) magnetic polaron

It is shown that, within deep narrow quantum potential wells in systems based on semimagnetic semiconductors containing Mn²⁺ ions, both magnitude and sign of the exchange interaction between electrons in the conduction band and in the d-shell of a magnetic ion depend significantly on the spatial position of this ion. This situation allows magnetic polarons with zero magnetic moment to appear, for which the localized-electron-induced spatial distribution of polarization of the surrounding magnetic ions exhibits an antiferromagnetic character. The possibility of experimental detection of these “nonmagnetic” magnetic polarons is considered.     

Thermal Behaviour of Ammonium Oxofluorotitanates(IV)

The thermal behaviour of ammonium oxofluorotitanates (NH₄)₃TiOF₅, (NH₄)₂TiOF₄ and NH₄TiOF₃ was investigated by thermoanalytical, X-ray and IR spectroscopic methods. The first decomposition stages under quasi-isobaric conditions are characterized by the formation of (NH₄)₂TiF₆ and ammonium oxofluorotitanate with the less content of ammonium and fluorine than in the initial compound. The decomposition process is accompanied by the Ti(IV) reducing due to ammonia evolved. The new ammonium oxofluorotitanate of high volatility was isolated and characterized. Ammonium-containing non-stoichiometric titanium oxyfluorides are the final products of thermal decomposition of ammonium oxofluorotitanates.This revised version was published online in November 2005 with corrections to the Cover Date.     

LiBaAlF6 and the crystal chemistry of LiAIIBIIIF6 phases

Lithium barium hexafluoroaluminate (LBAF), LiBaAlF₆, is a new member of the large family of compounds of formula LiA^IIB^IIIF₆. These materials display a variety of structures depending on the sizes of the A and B cations. LiBaAlF₆, which is isomorphous with LiBaCoF₆, belongs to the monoclinic P2₁/c subset and has a three‐dimensional network structure consisting of distorted LiF₄³⁻ tetrahedra corner‐sharing with AlF₆³⁻ octahedra and BaF₁₂ polyhedra. All of the atoms reside on general positions. An analysis of the ionic radii of the A cations versus formula volumes for the known members of the family yields a structure map that reasonably segregates the compounds by space group. The data obtained are thus suitable for predicting new isomorphic crystal structures.     

Formation of a nuclear spin polaron under optical orientation in GaAs-type semiconductors

A theory is developed for the formation of a nuclear spin polaron under optical cooling of nuclear spins in the vicinity of donor centers. It is shown that the polaron does not form above a certain limiting nuclear-spin temperature. For a shallow donor in GaAs, this temperature is about 10⁻⁷ K. The formation of a nuclear spin polaron should manifest itself in an anomalous increase of the spin relaxation time of the total spin of its component nuclei. Fiz. Tverd. Tela (St. Petersburg) 40, 1018–1021 (June 1998)