Effect of Barium Codoping on Superconductivity in SrxBi2Se3

JETP Letters - A structural reason for superconductivity in a Cu-, Sr-, or Nb-atom-doped Bi2Se3 topological insulator is still unclear. To understand this reason, a codoping approach has been...     

Nucleophilic addition of bifunctional sulfimidosulfides to platinum(<Emphasis Type="SmallCaps">IV</Emphasis>)-coordinated nitriles

Reactions of the platinum(IV) nitrile complexes [PtCl₄(RCN)₂] (R = Me, CH₂Ph, Ph) with 1,2- and 1,4-PhS(=NH)C₆H₄SPh in CH₂Cl₂ afforded addition products of sulfimides and coordinated nitriles, viz., the [PtCl₄{NH=C(R)N=S(Ph)(C₆H₄SPh)}₂] complexes. The latter were isolated in 75—90% yields and characterized by elemental analysis, positive-ion FAB mass spectrometry, IR spectroscopy, and ¹H and ¹³C¹H NMR spectroscopy. The temperature dependence of the ¹H NMR spectra of the model [PtCl₄{NH=C(R)N=SPh₂}₂] complexes (R = Me, Et) in CD₂Cl₂ studied in a temperature range from +40 to -70 °C demonstrated that E—Z isomerization of the ligands is a dynamic process in a range from +40 to -10 °C. The activation free energy of this process was calculated.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1618–1622, August, 2004.     

New analogs of D-homoequilenine with substituents in the D ring

Stereoselectivity of reaction with Raney nickel of D-homoestra-1,3,5(10),8,14-pentaenes containing one or two methyl groups in position 16 was investigated. The reaction direction is governed by the orientation of the substituent at C^17a. The signals in the ¹H and ¹³C NMR spectra of four synthesized compounds were completely assigned. Criteria for evaluation of the character of rings junction in analogs of D-homoequilenine were suggested. 16,16-Dimethyl-3-methoxy-D-homo-13α-estra-1,3,5(10),6,8-pentaen-17a-one was subjected to X-ray diffraction analysis.     

H, C NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5-endo,6-exo,8,9,9,10,10-octachloro-2-bornene and their DFT/GIAO C chemical shifts

The ¹H and ¹³C NMR chemical shifts for six toxaphene congeners: 2-exo,3-endo,6-exo,8,9,10-hexachloro- (1), 2-exo,3-endo,5-exo,9,9,10,10-heptachloro- (2), 2-exo,3-endo,6-exo,8,9,10,10-heptachloro- (3), 2-exo,3-endo,5-exo,6-endo,8,9,10-heptachloro- (4), 2-exo,3-endo,5-exo,6-endo,8,9,9,10-octachlorobornane (5) and 2,5-endo,6-exo,8,9,9,10,10-octachloro-2-bornene (6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) ¹H,¹H correlation spectroscopy (COSY), PFG ¹H,¹³C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG ¹H,¹³C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers (6a,6b) were elucidated by ab initio MO method and single point DFT/GIAO calculations for ¹³C chemical shifts. Theoretical calculations proved that the single crystal structure of 6 corresponds its most stable conformer in solution.     

Synthesis of Substituted Methyl Pyridazine-4-carboxylates via Cycloaddition of Diazomethane to 2,3-Disubstituted 2-Cyclopropenecarboxylic Acids

A three-step procedure has been developed for the synthesis of 3,5-disubstituted methyl pyridazine-4-carboxylates from accessible 2,3-disubstituted 2-cyclopropenecarboxylates. In the first step, cyclopropene derivatives react with diazomethane to give adducts having 2,3-diazabicyclo[3.1.1]hex-2-ene structure. The regio- and stereoselectivity of the cycloaddition has been determined. The second step is isomerization of the bicyclic adducts into 1,4-dihydropyridazine derivatives by the action of sodium methoxide. Finally, oxidation with potassium permanganate yields the target pyridazine-4-carboxylates.     

Study of the reaction of fluoroalkyl β-ketoesters with methylhydrazine by1H and19F NMR spectroscopy

Conclusions By¹H and¹⁹F NMR spectroscopy it was shown that reaction of fluoroalkyl -ketoesters with methylhydrazine in deuteromethanol at –30 to 30C involves intermediate formation of the -ketoester salts with methylhydrazine and 3,5-dioxypyrazolidines which successively split off methanol and H₂O with formation of 3-oxypyrazolines and pyrazol-5-ones, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 399–402, February, 1988.     

Oxidative addition of N-aminophthalimide to 2-alkenyl-1,3,4-oxadiazoles. Synthesis of aziridinyloxadiazoles

Oxidation of N-aminophthalimide with lead tetraacetate in the presence of 2-[(E)-2-arylethenyl]-5-phenyl-1,3,4-oxadiazoles gives the corresponding 2-(3-aryl-1-phthalimidoaziridin-2-yl)-5-phenyl-1,3,4-oxadiazoles. From 2-phenyl-5-[(1E,3E)-4-phenylbuta-1,3-dien-1-yl]-1,3,4-oxadiazole only the addition product at both C=C bonds was obtained, while in the reaction with 2,5-bis[(E)-2-phenylethenyl]-1,3,4-oxadiazole both mono- and bis-adducts were isolated.     

Ammonia-sensing properties of acridine immobilized in SiO2 sol-gel films

The spectral and luminescent properties of acridine in SiO₂ films synthesized by the sol-gel method using acid hydrolysis of tetraethoxysilane are studied. It is shown that acridine in films exists in protonated form. Ammonia-gas-sensing properties of films doped with acridine are studied by the fluorescence response (decrease in the intensity) of the protonated form. The possibility of multiple use of a sample without a noticeable decrease in its sensitivity is demonstrated. It is shown that the fluorescence response to a maximal permissible concentration of ammonia in the gas mixture with argon is 6–8%.     

Synthesis of 2-aryl(hetaryl)-1-hydroxyimidazoles by the reaction of aliphatic 1,2-hydroxylamino oximes with aromatic and heteroaromatic aldehydes

A reaction of aliphatic 1,2-hydroxylamino oximes bearing the hydroxylamino group at the secondary carbon atom with aromatic and heteroaromatic aldehydes in acetic acid leads to the corresponding 1-hydroxy-2-aryl(hetaryl)-4,5-dialkylimidazoles in high yields. α-Aryl(hetaryl)-nitrones initially formed by the condensation of 1,2-hydroxylamino oximes with aldehydes are quantitatively converted to the corresponding imidazoles.