[en] Polymeric nitrogen is a promising candidate for a high-energy-density material. Synthesis of energetic compounds with high chemical stability under ambient conditions is still a challenging problem. Here we report a theoretical study on yttrium nitrides by first principles calculations combined with an effective crystal structure search method. It is found that many yttrium nitrides with high nitrogen content can be formed under relatively moderate pressures. The results indicate that the nitrogen-rich YN₅ and YN₈ compounds are recoverable as metastable high-energy materials under ambient conditions, and can release enormous energies (2.51 kJ·g⁻¹ and 3.18 kJ·g⁻¹) while decomposing to molecular nitrogen and YN. Our findings enrich the family of transition metal nitrides, and open avenues for design and synthesis of novel high-energy-density materials. (paper)

[en] Alloy nitrides (U, Zr), (U, Ce), and (U, Y) were prepared and exposed to vacuum at temperatures to 1700⁰C and compared with pure UN. Weight loss data and physical observations showed that the alloy samples were more stable than UN. In weight loss, (U, Zr)N was 3 times as stable as UN at 1600⁰C for 100 h at 0.000002 torr (0.000266n/sq.m.). (U.S.)

No abstract available

No abstract available

[en] A possibility of the O→C_sp 1,4-migration of the R₃Si group in silyl ethers of terminal acetylenic alcohols upon treatment with organolithium reagents (RLi) was studied. In the case of 3-trimethylsilyloxypropyne, depending on the nature of RLi, the heterolysis of the Si—O bond occurs either by the action of acetylide formed as a result of deprotonation with the formation of 3-trimethylsilylprop-2-yn-1-ol trimethylsilyl ether, or by the action of the metalation agent with the formation of propargyl alcohol. The realization of the O→C_sp 1,4-migration of the Me₃Si group requires the use of mild organolithium reagents (lithium hexamethyldisilazanide and diisopropylamide). Silyl ethers having steric hindrance at the carbon atom bonded to the reaction center or around the silicon atom do not react with the studied organolithium reagents.

[en] Microstructure and phase composition of yttrium of various purity were studied by metallography and X-ray phase analysis. The investigation technique and characteristics of impurity phases are presented: YN, I₂O₃, YOF. The conclusion is made that the metallography method makes it possible to detect and identify impurity phases in commercial yttrium

[en] The very large enhancement of the Curie temperature in the novel ferromagnetic nitride Y₂Fe₁₇N₃ results from the obvious change of the electronic structure compared with that of its paternal compound Y₂Fe₁₇. Their electronic structures in both spin-polarized and non-spin-polarized states are calculated in the local spin-density functional approximation. From the band structure obtained by us, the Curie temperature of these compounds is calculated by including the effects of both the Stoner excitation and the spin fluctuation on the basis of the theory of Mohn and Wohlfarth without any adjustable parameters. The calculated enhancement of the Curie temperature for the nitride Y₂Fe₁₇N₃ is in good agreement with the measurement. Our results concerning the enhancement of the Curie temperature T_C for this ferromagnet upon nitrogenation suggest that the spin fluctuation is an important factor for this class of compounds, while the Stoner excitation must be involved in the calculation as well. (author)

[en] Study of the intramolecular cyclization of [3-(4-bromo(or methyl)phenylprop-2-yn-1-yl](3-phenylprop-2-en-1-yl)ammonium bromides has shown that the presence of a bromine atom or methyl group in the para position of the aromatic ring inhibits the process. 6-Bromo(or methyl)-4-phenyl-2,3,3a,4-tetrahydro-1H-benzo[f]isoindol-2-ium bromides undergo cleavage in aqueous alkaline medium at both N²-C³ and C¹-N² bonds, whereas cleavage of 6-methyl-4-phenyl-1,3,3a,4-tetrahydrospiro[benzo[f]isoindole-2,4′-morpholin]-2-ium bromide follows only the latter path. An accessible method has been developed for the synthesis of 6-bromo(or methyl)-4-phenyl-2,3,3a,4-tetrahydro-1H-benzo[f]isoindol-2-ium bromides, isomeric N-[7-bromo-2(3)-methyl-1-phenylnaphthalen-3(2)-ylmethyl]piperidines and -morpholines, and their 7-methyl-substituted analogs.

[en] Decomposition pressure-temperature relations have been determined experimentally for YN and Usub(1-x)Ysub(x)N (x = 0.25, 0.5, 0.75). These results agree well with theoretical equation: log psub(N₂)[Usub(1-x)Ysub(x)N] = (1 - x) log psub(N₂)[UN] + x log psub(N₂)[YN], which may be derived from thermodynamic considerations of the decomposition reaction of Usub(1-x)Ysub(x)N based on the reaction: Usub(1-x)Ysub(x)N(s) = Usub(1-x)Ysub(x)(1) + 1/2 N₂(g). Statistical thermodynamic calculations based on the linearity of the isotherms in the log psub(N₂)[Usub(1-x)Ysub(x)N] vs. YN mole fraction show that the interaction between U and N and that between Y and N in Usub(1-x)Ysub(x)N may be attractive, having the same order of magnitude. (Auth.)

[en] The catalytic properties of lanthanide amide, imide and nitride prepared by the use of liquid ammonia solutions of lanthanide metals (Ln=Eu and Yb) were studied for catalytic hydrogenation. The reaction of Eu or Yb metal solutions in liquid ammonia with silica yielded SiO₂-grafted lanthanide amide in the divalent state. The divalent amide showed catalytic activity for the selective hydrogenation of dienes and benzene. It was found that partial hydrogenation of benzene occurred with a very high selectivity for cyclohexene. Amides of calcium, strontium and barium were examined similarly in connection with catalytic studies on divalent amides. Imide and nitride, into which the lanthanide (Ln/AC) deposited by impregnation of active carbon (AC) with liquid ammonia solutions of lanthanide metals were converted thermally, were studied catalytically. It was concluded that imide or imide-like species generated during the thermal degradation of lanthanide amide to nitride were very active in the hydrogenation of ethene. Lanthanide nitride was virtually inactive, but the nitride highly dispersed on active carbon was activated when subjected to evacuation treatment above about 1000 K. (orig.)