Some thermodynamic aspects of nitrides in materials science

The energies of combustion in fluorine of gallium nitride and indium nitride in wurzite crystalline structure have been measured in a two-compartment calorimetric bomb, and new standard molar enthalpies of formation have been calculated: Δ_fH_m⁰(GaN(cr) 298.15 K)= –(163.7±4.2) kJ mol^–1 and Δ_fH_m⁰(InN(cr) 298.15 K)= –(146.5±4.6) kJ mol^–1 . Comparison with the recommended values of the Δ_fH_m⁰ nitrides from the literature is also presented.     

Syntheses and structures of six compounds in the A2LiMS4 (A=K, Rb, Cs; M=V, Nb, Ta) family

Six new compounds in the A₂LiMS₄ (A=K, Rb, Cs; M=V, Nb, Ta) family, namely K₂LiVS₄, Rb₂LiVS₄, Cs₂LiVS₄, Rb₂LiNbS₄, Cs₂LiNbS₄, and Rb₂LiTaS₄, have been synthesized by the reactions of the elements in Li₂S/S/A₂S₃ (A=K, Rb, Cs) fluxes at 773 K. The A and M atoms play a role in the coordination environment of the Li atoms, leading to different crystal structures. Coordination numbers of Li atoms are five in K₂LiVS₄, four in A₂LiVS₄ (A=Rb, Cs) and Cs₂LiNbS₄, and both four and five in Rb₂LiMS₄ (M=Nb, Ta). The A₂LiVS₄ (A=Rb, Cs) structure comprises one-dimensional chains of tetrahedra. The Rb₂LiMS₄ (M=Nb, Ta) structure is composed of two-dimensional layers. The Cs₂LiNbS₄ structure contains one-dimensional chains that are related to the Rb₂LiMS₄ layers. The K₂LiVS₄ structure contains a different kind of layer.     

Synthesis, crystal structures and ionic conductivities of Bi14P4O31 and Bi50V4O85. Two members of the series Bi18−4mM4mO27+4m (M=P, V) related to the fluorite-type structure

The two hitherto unknown compounds Bi₁₄P₄O₃₁ and Bi₅₀V₄O₈₅ were prepared by the direct solid-state reaction of Bi₂O₃ and (NH₄)H₂PO₄ or V₂O₅, respectively. Bi₁₄P₄O₃₁ crystallizes in a C-centred monoclinic symmetry (C2/c space group) with the unit-cell parameters: , , and β=93.63(1)° (Z=16). The symmetry of Bi₅₀V₄O₈₅ is also monoclinic (I2/m space group) with lattice parameters of , , and β=90.14(1)° (Z=2). Both structures correspond to a fluorite-type superstructure where the Bi and P or V atoms are ordered in the framework. An idealized structural model is proposed where the structures result of the stacking of mixed atomic layers of composition [Bi₁₄M₄O₃₁] and [Bi₁₈O₂₇] respectively. This new family can be formulated Bi_18−4mM_4mO_27+4m with M=P, V and where the parameter m (0?m?1) represents the ratio of the number of [Bi₁₄M₄O₃₁] layers to the total number of layers in the sequence. Bi₁₄P₄O₃₁ corresponds to m=1 when Bi₅₀V₈O₈₅ corresponds to m=1/3. In this last case, the structural sequence is simply one [Bi₁₄V₄O₃₁] layer to two [Bi₁₈O₂₇] layers. As predicted by the proposed structural building principle, Bi₁₄P₄O₃₁ is not a good ionic conductor. The conductivity at 650 °C is 4 orders of magnitude lower from those found in Bi₄₆M₈O₈₉ (M=P, V) (m=2/3) and Bi₅₀V₄O₈₅ (m=1/3).     

甲状腺机能亢进症头发锌、硒、钒、锂、锗5种微量元素的动态变化

测定了２４例甲亢治疗前后及３０例健康对照的头发锌、硒、钒、锂及锗的含量，发现未治疗的甲亢头发锌、硒、钒、锂及锗含量较对照组低，Ｚｎ、Ｓｅ、Ｌｉ、Ｇｅ，Ｐ＜０．００１，Ｖ，Ｐ＜０．０１．甲亢经６～１２周抗甲亢药物治疗后．头发中５种元素均较治疗前上升（Ｐ＜０．００１），且头发钒和锂含量治疗后已达到对照组水平，Ｖ，Ｐ＞０．２，Ｌｉ，Ｐ＞０．１，而头发锌、晒及锗含量治疗后仍低于对照组（Ｐ＜０　．００１）．结论：甲亢头发锌、硒、钒、锂及锗含量降低．经６～１２周抗甲亢治疗可使头发钒及锂含量恢复正常水平，而其余３种元素则可能需要更长时间的抗甲亢治疗才能恢复至正常水平。     

Quantum chemical studies on electrophilic addition

The geometries of the 2-aminoethyl cation and the isomeric protonated aziridine have been optimized using ab initio molecular orbital calculations employing the split-valence shell 4-31G basis set. The protonated aziridine is computed to be the more stable ion by 46.5 kcal/mole (4-31G level) and 44.9 kcal/mole (double-zeta basis set). The profile to interconversion is found to have a barrier of less than 15 kcal/mole (relative to the 2-aminoethyl cation) and this profile is compared with those computed for the similar ions XCH₂CH ₂ ⁺ where X=OH, F, SH and Cl.     

Crystal structure and single crystal EPR of (NH_4)_2(15-crown-5)_3[Cu(mnt)_2] and (NH_4)_2(benzo-15-crown-5)_4[Cu(mnt)_2]·0.5H_2O

The X-ray crystal structures of (NH4)2(15-crown-5)3[Cu(mnt)2] (1) and (NH4)2(benzo-15-crown-5)4- [Cu(mnt)2]·0.5H2O (2) were determined. Two single crystals are composed of distinct structures of ammonium-crown ether supramolecular cation and [Cu(mnt)2]2? anion. The triple-decker dication in complex 1 and a sandwich dimmer in complex 2 were observed. X-Band EPR studies on the single crystals of both complex 1 and complex 2 have been carried out at room temperature, which revealed that complex 2 showed a perfect hyperfine structure of Cu whereas that of complex 1 could not be observed. The principal values and direction cosines of the principal axes of the g and A tensors were computed by a least-squares fitting procedure. The spin density of Cu(II) was estimated according to the principal values of the A tensors and compared well with the results calculated based on DFT method.     

Electrochemistry of vanadium-doped tetragonal and monoclinic ZrO2 attached to graphite/polyester composite electrodes

The electrochemistry of monoclinic and tetragonal vanadium-doped zirconias (VZrO₂), prepared from gel precursors with vanadium loadings ranging from 0.5 to 15 mol%, has been studied using abrasive-conditioned graphite/polyester composite electrodes immersed in aqueous HCl and HClO₄ solutions. Isolated vanadium centers form a solid solution in the zirconia lattice with a solubility limit close to 5 mol%. Above 5 mol%, finely dispersed V₂O₅ is formed. Vanadium centers located at the boundary sites of the zirconia lattice display successive one-electron transfer processes near to +0.25 and +0.10 V vs. SCE, whereas finely dispersed V₂O₅ yields three successive reduction processes at +0.46, +0.30, and +0.16 V vs. SCE. Electrochemical data indicate the presence of both V⁵⁺ and V⁴⁺ centers in the lattice of monoclinic and tetragonal zirconias, the V⁵⁺/V⁴⁺ ratio decreasing as the vanadium loading increases. Electronic Publication     

Reactions of salicylaldehyde with tris(pentaf luorophenyl)silanes and secondary amines

Reactions of tris(pentafluorophenyl)silanes RSi(C₆F₅)₃ with salicylaldehyde and secondary amines were studied. The reactions afforded α-pentafluorophenyl-substituted amines. Silanes RSi(C₆F₅)₃ (R = Me, Ph, C₆F₅, CH₂CH=CH₂, and CH=CH₂) were found to be efficient reagents for transfer of the C₆F₅ group to the iminium cation generated from salicylaldehyde and amine. However, tris(pentafluorophenyl)phenylethynyl-and tris(pentafluorophenyl)silanes were not able to serve as a source of a fluorinated substituent because of competitive transfer of acetylenide fragment or hydride. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 498–503, March, 2006.     

阳离子交换树脂的有机催化进展

综述了聚苯乙烯型磺酸树脂、全氟磺酸树脂Nafion及崭新的Nafion／siO_2复 合催化剂在有机合成中应用的最新进展．     

Surface cavities produced by high‐dose nitrogen ion implantation into silicon

Nitrogen ion implantation (24 keV, 4.6 × 10¹⁷ cm^?2) into (100) a p‐type silicon wafer material and a subsequent electron beam annealing at 1100 °C for 15 s under high vacuum conditions leads to the formation of an uneven surface in the implanted region caused by nitrogen bubbles beneath the surface. Annealing at 1200 °C for 300 s results in surface cavities with a mean diameter of 350 nm and a surface coverage of 3–4% and an average depth of ～60 nm. Nuclear reaction analysis reveals that the nitrogen concentration in the as‐implanted state exceeds 57 at%, the value of stoichiometric Si₃N₄. Annealing at 1100 °C for 15 s slightly reduces the nitrogen peak concentration, whereas annealing at 1200 °C for 300 s induces a significant alteration to the shape of the nitrogen depth profile coupled with the lowering of the concentration close to the stoichiometry of Si₃N₄. The results present a new method of producing sub‐micrometre cavities embedded in a thin silicon nitride film on wafer silicon which may lead to novel micro‐electronic and biotechnology applications. Copyright © 2007 John Wiley & Sons, Ltd.