Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

Terminal bis-acetylenes derived from 1,2-bis(1<Emphasis Type="Italic">H</Emphasis>-tetrazol-5-yl)ethane

The N(1)—N(1), N(2)—N(2), and N(1)—N(2) regioisomers of 1,2-bis[(prop-2-yn-1-yl)-1H-tetrazol-5-yl]ethane were first synthesized by alkylation of 1,2-bis(1H-tetrazol-5-yl)ethane with propargyl bromide. The peculiarities of the crystal structure of 1,2-bis[1-(prop-2-yn-1-yl)-1H-tetrazol-5-yl]ethane were evaluated by X-ray diffraction analysis. This compound is readily underwent Cu-catalyzed [3+2] cycloaddition with p-tolyl azide, p-nitrophenyl azide, and benzyl azide to give heterocyclic assembles bearing 1,2,3-triazole and tetrazole cycles. Catalyst-free [3+2] cycloadditions of 1,2-bis[1-(prop-2-yn-1-yl)-1H-tetrazol-5-yl]ethane and the mixtures of the N(1)—N(1), N(2)—N(2), N(1)—N(2) regioisomers with poly(glycidyl azide) oligomers resulted in 1,2,3-triazole cycles and crosslinking of the polymer chains.     

Synthesis of bis(polyfluoroalkyl)-1,3,5-triketones

A preparative procedure was developed for the synthesis of polyfluoroalkyl-1,3,5-triketones by condensation of acetone or fluorinated methyl -diketones with methyl perfluorocarboxylates in the presence of LiH. In the case of CF₃ substituents, the formation of triketone was accompanied by the formation of its cyclic hydrate, viz., of dihydroxytetrahydropyranone.     

Synthesis and Tautomeric Equilibrium of Polyfluoroacyl-Containing 1,5-Benzodiazepines

The reaction of bis(polyfluoroalkyl)-containing 1,3,5-triketones with o-phenylenediamine yielded 2-polyfluoroacylmethylene-4-polyfluoroalkyl-1,3- or 1,5-dihydro-1,5-benzodiazepines. The tautomeric equilibrium of the obtained benzodiazepines in CDCl₃, CD₃CN, DMSO, and DMF solution was studied.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

Heterospin complexes of fluorinated dinuclear Cu<Superscript>II</Superscript> and Mn<Superscript>II</Superscript> triketonates with nitroxides

Dinuclear heterospin complexes of Cu^II and Mn^II 1,1,1,7,7,7-hexafluoroheptane-2,4,6-trionates ([Cu₂L₂] and [Mn₂L₂], respectively) with nitronyl nitroxides 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide 1-oxyls (NIT-R, R = H, Me, Et, m-C₅H₄N, m-NCC₆H₄, p-NCC₆H₄, PzMe) and the diradical NIT-Pz-(CH₂)₄-Pz-NIT (Pz is 1,4-pyrazolylene) were synthesized and structurally characterized. In the complexes under study, the CuII atom tends to have the square-pyramidal coordination environment, and the MnII atom is in an octahedral environment. The magnetochemical investigation of the compounds in the temperature range of 2–300 K showed that the antiferromagnetic exchange coupling dominates in the [Cu₂L₂] molecules, whereas this coupling in [Mn₂L₂] is manifested in the experimental plot μ_eff(T) at T < 100 K. The magnetic properties of the heterospin complexes of [Cu₂L₂] with NIT-R are also determined by the intramatrix antiferromagnetic exchange coupling. For the complexes of [Mn₂L₂] with NIT-R, the coordination mode of the nitroxide plays a decisive role.     

Unusual transformations of lithium enolate of ethyl 4,4,4-trifluoro-3-oxobutanoate

The present paper describes unusual reactions of lithium enolate of ethyl 4,4,4-trifluoro-3-oxobutanoate with ammonium acetate and 1-aminonaphthalene. These reactions produce 4-amino-2,6-bis(trifluoromethyl)pyridine and 4-trifluoromethyl-2-[(Z)-1,1,1-trifluoroprop-1-en-2-ol-1-yl]benzo[h]quinoline, respectively. The reaction of 1,1,7,7,7-hexafluoroheptane-2,4,6-trione hydrate with 1-naphthylamine gives a mixture of 4-trifluoromethyl-2-[(Z)-1,1,1-trifluoroprop-1-en-2-ol-1-yl]benzo[h]quinoline and N,N??-bis(naphth-1-yl)-2,6-bis(trifluoromethyl)pyridine-4(1H)-imine, respectively.