Synthesis of crown-containing and related hetarylphenylacetylenes and acetylenyl dyes

New 15(18)-crown-5(6)-containing and model methoxy-substituted 1-hetaryl-2-phenylacetylenes of the 4-pyridine and 2-benzothiazole series were synthesized using the addition of bromine to the ethylene fragment of the corresponding styrylheterocycles followed by dehydrobromination under the action of potassium tert-butoxide. The quaternization of the pyridylphenylacetylenes afforded new acetylenyl dyes. The structures of five synthesized compounds were determined by X-ray diffraction analysis.     

Spectral properties of protonated naphthylpyridine in the presence of cyclodexrins

Electronic absorption and fluorescence spectroscopy showed that the addition of 2-hydroxypropyl cyclodextrin derivatives (HP-α-CD, HP-β-CD, and HP-γ-CD) to an aqueous solution of 4-(2-naphthyl)pyridinium perchlorate (2) results in its partial deprotonation and formation of an inclusion complex of 4-(2-naphthyl)pyridine (1) with the cavitand. The stoichiometry and stability of the inclusion complexes of compounds 1 and 2 and 1-methyl-4-(2-naphthyl)-pyridinium perchlorate (3) with cyclodextrins and their hydroxypropyl derivatives (logK = = 1.5–2.7) were studied by ¹H NMR titration. Cyclodextrins with the neutral form 1 form more stable complexes than with ionic compounds 2 and 3. The protonation of the nitrogen atom of compound 2 in aqueous solutions can occur in both the ground and excited states, and the fluorescence spectrum exhibits only the band of the protonated form. Quantum chemical simulation of the deprotonation/protonation processes in an aqueous solution of compound 2 in the absence and presence of HP-β-CD was performed. A tendency for shifting the acid-base equilibrium towards the formation of deprotonated form 1 is observed upon the addition of 2-hydroxypropyl cyclodextrin derivatives to the solution.     

Magnetic properties of GdxLa1−x CoSi

The magnetic properties and crystal structure of Gd_xLa_1−x CoSi compounds (x=0, 0.25, 0.5, 0.65, 0.8, 1) are investigated. The anisotropy of the magnetic properties are analyzed for a GdCoSi single crystal. The temperature dependences of the magnetic susceptibility and the tetragonal lattice parameters of GdCoSi are characterized by anomalies in the vicinity of the magnetic phase transition temperatures, 166 K and 300 K. The Néel temperatures, the effective magnetic moments, and the paramagnetic Curie temperatures of these compounds decrease as gadolinium is replaced by lanthanum. The compound LaCoSi is a Pauli paramagnet. The results are discussed on the basis of a model that takes into account the presence of positive and negative exchange interactions and the itinerant magnetism of the cobalt sublattice. Fiz. Tverd. Tela (St. Petersburg) 39, 1270–1274 (July 1997)     

Influence of oxygen partial pressure on properties 12zsolid solutions

The annealing of YBa₂Cu_zO_7−δcompounds (2.5 ≤ z ≤ 3.5) in oxygen flow (at temperature of synthesis and following fast cooling) leads to: (i) a reduction in homogeneity range; (ii) decreasing of copper content influence on superconducting properties of samples; (iii) considerable decreasing of ΔT_cvalue as a result of cation and anion vacancies order.     

Structure and superconducting properties of Bi2Ba2−xMxCuO6+δ

The effect of oxygen nonstoichiometry and barium cation substitution on the structure and superconducting properties of Bi₂Ba_2−xM_xCuO_{6 +δ}(M = Sr, Ru, Rh, Pd, In, Sb or Pb;xchanged from 0 to 0.2) were studied. The cation-substituted samples annealed in oxygen flow contain a superconducting phase withT_c^initnear 95 K.     

Transport properties of Mg2 X 0.4Sn0.6 solid solutions (X = Si, Ge) with p-type conductivity

The transport properties of Mg₂ X _0.4Sn_0.6 (X = Si, Ge) solid solutions are investigated. It is shown that these materials can be rendered p-type with a hole concentration of up to 4 × 10¹⁹ cm^?3. The Hall coefficient, thermopower, and electrical conductivity are measured over a wide temperature range. The mobility of holes in these solid solutions is less than that of electrons by a factor of 2 for Mg₂Si_0.4Sn_0.6 and by a factor of 1.5 for Mg₂Ge_0.4Sn_0.6. Solid solutions in the Mg₂Ge-Mg₂Sn system appear more promising for thermoelectric applications.     

Kinetic properties of p-Mg2SixSn1 ? x solid solutions for x < 0.4

The results of a study of Mg₂Si _x Sn_{1 − x} solid solutions (x = 0.25, 0.3, 0.35, 0.4) are reported. The measurements performed cover the Seebeck coefficient, electrical conductivity and the Hall coefficient over broad ranges of temperatures (80–700 K) and carrier concentrations (10¹⁸ to 6 × 10²⁰ cm⁻³). These measurements were used to derive the band structure parameters (band gap, hole mobility, hole effective mass). The effective mass of holes was found to grow strongly with an increase in their concentration.