Stable Isomers of Sila - and Germadodecahedrane. a Semiempirical (Am1) Investigation of the Structure of 4/6 and 4/5/6 Ring Containing E20 (E=SI, GE) Systems

AMI molecular orbital calculations with full geometry optimisation of 4/6, 5/5 and 4/5/6 isomers of E₂₀ (E=Si, Ge) show a clear preference of germanium to be accommodated in four membered rings and to achieve coordination numbers greater than 3 (V A). as a consequence, unlike C₂₀ or Si₂₀, the dodecahedral form of Ge₂₀ was not localised on the potential surface, instead an opened structure derived from an octagermaprismane (IV B) can be predicted. Notable kinetic stabilisation in the (SiR)₂₀ systems is suggested by the HOMO-LUMO differences.     

Possible C20 Isomers Containing 4/6 Rings. As Ami Investigation of the Stability of Three 4/6 Cages and of Their Hydrogenated Analogues

Semiempirical AM1 calculations on isomers (I-III) of C₂₀ constructed from six and four-membered rings reveal high enthalpies of formation compared to the dodecahedral or the planar cyclic isomers. Hydrogenation of I-III however reduces greatly their enthalpies of formation and increase the HOMO-LUMO differences making such species interesting targets for synthesis.     

Facile synthesis of 1-(N-butyl-1,8-naphthalimide-4′-yl)-3-(4-methoxyl-phenyl)-5-phenyl-pyrazoline/polyaniline core-shell nanofibers and polyaniline nanotubes

1-(N-butyl-1,8-naphthalimide-4′-yl)-3-(4-methoxyl-phenyl)-5-phenyl-pyrazoline (BMPP)/polyaniline core-shell nanofibers were synthesized by in situ chemical oxidative polymerization of aniline using BMPP nanofibers as template. BMPP/polyaniline core-shell nanofibers exhibited uniform fibrilliar morphology and possessed BMPP nanofiber core and polyaniline shell, which existed in the form of nanoparticles. BMPP nanofibers were fabricated by the modified reprecipitation method with water as poor solvent. After BMPP/polyaniline core-shell nanofibers were washed with ethanol as good solvent to remove BMPP cores, polyaniline nanotubes with netlike structures were obtained. The molecular structures of BMPP/polyaniline nanocables were characterized by Fourier transform infrared spectroscopy and UV-vis spectroscopy, respectively. The core/shell structures of BMPP and polyaniline endowed BMPP/polyaniline core-shell nanofibers good electrochemical properties in comparison with BMPP nanofibers.     

XRD and optical microscopic studies of Co(III) complexes containing 5-cyano-6-(4-pyridyl)-2-thiouracil, thymine and adenine bases

Multifunctional ligand 5-cyano-6-(-4-pyridyl)-2-thiouracil (L) was prepared and allowed to react withtrans [Co(en)₂Cl₂]⁺Cl^‡ resulting into [Co(en)₂LCl]²⁺.2Cl^- which upon further reaction with equimolar ratio of ligand [L] gave the complex [Co(en)₂L₂]³⁺.3Cl⁻. These metal complexes were then separately reacted with thymine and adenine bases. Complexes thus prepared after characterization by their elemental analysis, FAB mass and spectral (IR,¹ HNMR, UV-visible) data were studied for their powder X-ray diffraction and optical microscopic characteristics.     

Infrared and Raman Investigations of the Charge Ordering Phenomena in the Monoclinic Salts κ-(BEDT-TTF)4[M(CN)6][N(C2H5)4]·2H2O (M = CoIII, FeIII)

The monoclinic crystals of κ-phase charge-transfer salts formed by BEDT-TTF with Co(CN)₆ or Fe(CN)₆ anions undergo a phase transition at T = 150 K. Temperature dependences of FT-NIR Raman spectra and IR reflectance spectra were studied. We show that the phase transition is related to a charge ordering and there exist charge fluctuations above 150 K.     

PMN-PT弛豫铁电固溶体的定向凝固组织与结晶习性

研究了(1-x)Pb(Mg1／3Nb2／3)O3-xPbTiO3(简称PMN—PT或PMNT)系铁电固溶体在坩埚下降法定向凝固过程中的结晶与晶粒生长习性．结果表明，随着坩埚下降速度的加快和PbTiO3含量的降低，陶瓷晶粒的择优生长方向由[111]逐渐向[110]转变．     

Magnetocaloric effect of (ErxR1−x)Co2 (R = Ho, Dy) for magnetic refrigeration between 20 and 80 K

Two series of RCo₂ compounds, (Er_xHo_1−x)Co₂ and (Er_yDy_1−y)Co₂, were investigated as magnetic refrigerants for hydrogen liquefaction. A large magnetocaloric effect (MCE) was observed just above the Curie temperature (T_c) of these compounds which both undergo a first-order magnetic transition. The isothermal entropy change ΔS and the adiabatic temperature change ΔT_ad of these compounds were larger than those of other Laves-phase materials such as RAl₂ and RNi₂. However, the temperature range of the large MCE for these compounds was limited. It has been shown that T_c increases almost linearly against the de Gennes factor, and can be controlled by changing the concentration of the rare earth elements while maintaining a first-order transition. By measuring the magnetization and heat capacity, we obtained temperature entropy (T–S) diagrams, which are essential for analyzing the magnetic refrigeration cycle. Both series of compounds showed high potential for use in a regenerative thermal cycle, especially as a combination of several compositions to cover a wide temperature range.     

CaTiO3对(1-x)ZnAl2O4-xMg2TiO4(x=0.21)微波介质陶瓷结构和性能的影响

利用常规固相法制备了ZnAl₂O₄-Mg₂TiO₄-CaTiO₃陶瓷, 研究了CaTiO₃对其相成分、微观组织结构和微波介电性能的影响规律. 结果表明, CaTiO3能有效地改善(1-x)ZnAl₂O₄-xMg₂TiO₄(x=0.21)材料的烧结性能, 使其致密化温度降低150℃. ZnAl₂O₄-Mg₂TiO₄-CaTiO₃陶瓷体系中包括ZnAl₂O₄基尖晶石相、CaTiO₃、MgTi₂O₅和Zn₂Ti₃O₈相, 当烧结温度高于1400℃时, Zn₂Ti₃O₈相消失. 随着CaTiO₃含量的增加, 体系中CaTiO₃相含量增加而MgTi₂O₅相含量减少, 且CaTiO₃具有显著地调节谐振频率温度系数的作用. 当在(1-x)ZnAl₂O₄-xMg₂TiO₄(x=0.21)体系中掺入6mol%的CaTiO₃添加剂时, 经1400℃烧结后能获得温度稳定性好的微波介质陶瓷材料, 其微波介电性能为：ε_r=11.8, Q·f=88080GHz, τ_f=-7.8×10^－6/℃.     

聚乳酸／纳米二氧化硅复合材料分子量的影响因素

以丙交酯和改性后的纳米二氧化硅为原料,在催化剂作用下,用原位聚合法制备了聚乳酸纳米二氧化硅复合材料。讨论了催化剂的种类和用量、反应时间、反应温度、纳米二氧化硅的用量等因素对复合材料分子量的影响。结果表明,最优的反应条件为:采用辛酸亚锡为催化剂,催化剂用量和二氧化硅用量分别为丙交酯用量的0.25%(质量分数,下同)和5%,在140℃油浴中,氮气保护下反应72 h,可得到重均分子量为1.5091×105的聚乳酸纳米二氧化硅复合材料。     

Synthesis and crystal structure of [3,5-(CH3O)2C6H3NH3]4P4O12·4H2O

The chemical preparation and crystal structure are given for a new organic-cation cyclotetraphosphate. This compound is triclinic P-1 with the following unit cell parameters: a=7.857(1) Å, b=8.877(2) Å, c=17.271(3) Å, α=93.94(1)°, β=101.75(2)°, γ=103.72(1)° V=1137.0(4) Å³, Z=1 and ρ_cal=1.467 g cm⁻³. The crystal structure has been determined and refined to R=0.037, using 6291 independent reflections. The atomic arrangement can be described by inorganic layers parallel to the (0 0 1) planes, between which the organic entities are located.     

Crystal structure and characterization of [2,5-(CH3O)2C6H3NH3]4P4O12·2H2O

The preparation, crystal structure, TG–DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH₃O)₂C₆H₃NH₃]₄P₄O₁₂·2H₂O. This new compound is triclinic P with unit cell dimensions: a = 7.438(5) Å, b = 11.841(7) Å, c = 12.354(4) Å,  = 96.61(4)°, β = 98.35(4)°, γ = 102.60(6)°, Z = 1 and V = 1038.0(1) Å³. Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P₄O₁₂ ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds.     

Morphological, structural, optical and dielectric properties of 91SiO2:4Li2O:4Nb2O5:1Dy2O3 (% mole) glass prepared by sol–gel

We report on the structural, morphological and optical characterization of glass and glass–ceramic samples, with nominal composition of 91SiO₂:4Li₂O:4Nb₂O₅:1Dy₂O₃ (% mole). The samples were heated treated in air in the temperature range between 500 °C and 800 °C. The glass–ceramics samples start to crystallize at temperatures above 600 °C and besides the SiO₂ and LiNbO₃ crystalline phases, sub micron DyNbO₄ precipitates were identified by X-ray diffraction and scanning electron microscopy for temperatures above 750 °C. Using Raman spectroscopy was possible to identify the vibration modes assigned to the crystalline phases detected by the XRD analysis. Also, the performed Photoluminescence Spectroscopy analysis suggest that the optical activation of Dy³⁺ ions in the glass and glass–ceramics hosts was found to be dependent of the heat treatment temperature. Intraconfigurational transitions between the ⁴F_9/2 and ⁶H_{J(=15/2, 13/2)} multiplets of Dy³⁺ ions were only observed for samples without the presence of the DyNbO₄ crystalline phase. Moreover, for samples heat treated between 500 °C and 700 °C the intensity ratio of the ⁴F_9/2⁶H_13/2 and ⁴F_9/2⁶H_15/2 transitions of the lanthanide ion changes, suggesting different ion environments which are dependent on the thermal annealing temperature. The dielectric measurements revealed that ε′ value depends mainly in the number of network modifier ions and the relaxation phenomenon observed at frequencies above 10 kHz, in all samples, can be assigned to the increase of the volume ratio between the LiNbO₃ particles and the glass network.