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141.
Lin Peng Liang-Liang Wang Jian-Fei Bai Li-Na Jia Qing-Chuan Yang Qing-Chun HuangXiao-Ying Xu Li-Xin Wang 《Tetrahedron letters》2011,52(11):1157-1160
Cinchona alkaloids were first successfully reported to promote enantioselective Phospho-Aldol reaction of diphenyl phosphite to a variety of N-alkylated isatin derivatives in good to excellent yields (up to 99%) and moderate to good enantioselectivities (up to 73% ee) almost in no time. 相似文献
142.
Prof. Dr. Werner Uhl 《Angewandte Chemie (International ed. in English)》1993,32(10):1386-1397
In the attempt to synthesize compounds with aluminum in a low oxidation state and an Al Al bond, by the reduction of alkylaluminum halides with alkali metals, analogous to a Wurtz coupling, in general the deposition of elemental aluminum and the formation of the corresponding trialkylaluminum compounds is observed. Thus, tetrasubstituted dialuminum compounds R2Al AlR2, apart from a few poorly characterized examples, were for a long time considered part of an unverified class of substances. Only with the sterically very highly shielded tetrakis[bis(trimethylsilyl)methyl]dialuminum did we achieve the synthesis of the first completely characterized organoelement compound with unlimited stability, which shows aluminum in the oxidation state + II and has an Al Al bond. In the meantime, corresponding compounds for the elements gallium and indium have been obtained. With the simple access to tetrasubstituted dimetal compounds, a fascinating new research area has opened for preparative chemistry, in which the particular interest will naturally lie in the reactive properties of the metal-metal bond. 相似文献
143.
144.
Ga^3+的新萃取体系的界面特性和胶团化作用研究 总被引:1,自引:0,他引:1
研究了Ga~(3+)协萃体系(Ga~(3+)-D_2EHPA-H_2MPA-正十二烷-H_2SO_4)的界面吸附和胶团形成热力学,发现该萃取体系中[H_2MPA]影响D_2EHPA和H_2MPA的界面吸附性质。在中、高[H_2MPA]范围内D_2EHPA与H_2MPA的界面吸附行为相反,D_2EHPA的存在也影响H_2MPA的界面吸附行为。研究了界面张力与各因素关系的数学模型,并获得某些胶团形成和界面吸附特性的物化参数。 相似文献
145.
Jens Hartig Andreas Schnepf L. Jos de Jongh David Bono Hansgeorg Schnöckel Prof. Dr. 《无机化学与普通化学杂志》2007,633(1):63-76
Towards the Understanding of the Unexpected Properties of the Metalloid Cluster Compound [Ga84(N(SiMe3)2)20][Li6Br2(THF)20]·2Toluol In several short communications we have recently reported on the electrical and superconducting properties of the crystalline title compound 1 which contains anionic Ga84R20‐moieties. Here we present a collection of these results, complemented and interpreted by using DFT‐calculations on model clusters (Ga84(NH2)20?). These calculations allow a) a first insight into the dynamics of the Ga84‐moieties (e.g. a rotation of the central Ga2‐dumbbell) and thus an explanation of the temperature‐dependent Ga‐NMR‐spectra described recently, and b) estimations on the lattice energy of 1 and its resulting unexpected energetic stabilization compared to metallic gallium. A possible contribution of the cations in the electrical conduction mechanism of 1 can also be made feasible with model calculations. The basis for all the results presented is to be found in the “perfect” arrangement of nanoscopic Ga84‐clusters in the crystal. This theoretically predicted condition for superconductivity in a “chain” of identical metal cluster molecules is a requirement which can hardly be realized by means of physical fabrication methods. Therefore, on the one hand the results presented here make for some disillusionment in the field of nanoscience, but on the other hand, especially in the field of synthetic chemistry, they present rewarding challenges for fundamental work in the future. 相似文献
146.
Shinichi Kikkawa Kazuteru Nagasaka Mark Bailey Yoshinari Miyamoto 《Journal of solid state chemistry》2007,180(7):1984-1989
Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga0.89□0.11) (N0.66O0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750-850 °C. Approximately, 10 at% Li+ was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga3+ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li2Ga3NO4, was also obtained with Li2CN2 impurity using similar preparations from a mixture of Li/Ga?1. The crystal structure was isostructural with h-GaN, and was refined as P63mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li2CN2 impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO2. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm. 相似文献
147.
以三乙二醇为表面配体,利用沉淀法制备了β-Ga_2O_3∶Cr~(3+)近红外(NIR)长余辉纳米颗粒.考察了反应条件对β-Ga_2O_3∶Cr~(3+)的发光性能和晶体结构的影响,并初步探讨了其NIR余辉发光机理.结果表明,当溶液的p H值为7,煅烧温度为700℃时,可获得高纯度的β-Ga_2O_3∶Cr~(3+)纳米颗粒,其平均粒径为30 nm,最大余辉发射波长可调控为750 nm,NIR余辉发光时间长于384 h.本方法得到的β-Ga_2O_3∶Cr~(3+)长余辉纳米颗粒不仅尺寸小,而且NIR余辉时间长,发射波长可调控,在低背景噪音的深组织活体成像中具有潜在的应用前景. 相似文献
148.
Controlled potential coulometric (CPC) studies were carried out for developing a method to determine gallium at milligram levels, in the mixed supporting electrolyte medium (4 M NaClO4 + 0.5 M NaSCN), employing stirring mercury as a working electrode. Investigations for optimization of working electrode potentials, quantity of charge, level of background current and electrolysis time for achieving quantitative reduction of Ga(III) to Ga and its oxidation back to Ga(III), were undertaken. Effect of gallium content and interference of zinc in of gallium determination were also studied. The developed methodology was employed for the determination of gallium in pure Ga as well as in synthetic U + Ga mixture solutions. Accuracy and precision values of better than 0.5% were obtained at 1-2 mg levels. 相似文献
149.
Synthesis,Single Crystal Growth and Crystal Structure of Ta7Cu10Ga34 – a 8 × 4 × 2 Super Structure of CsCl
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Single crystals of Ta7Cu10Ga34 were grown from the elements in a Cu/Ga melt. Ta7Cu10Ga34 represents the first ternary compound of the system Ta/Cu/Ga. The crystal structure (Cmmm, oC102, Z = 2, a = 23.803(1), b = 12.2087(4), c = 5.7487(2) Å, 1291 refl. 78 parameters, R1 = 0.037, wR2 = 0.070). The crystal structure is characterized by rods of pentagonal prisms MGa10, which are alternatingly occupied by Ta and Cu. Four of these rods are connected to columns running in direction (001). These columns are linked by cubic units TaGa8, CuGa8, and GaGa8. According to the characteristic structural elements and the size of the unit cell Ta7Cu10Ga34 represents a 8 × 4 × 2 super structure of CsCl or bcc. With respect to the underlying CsCl structure the formula can be written as [Ta7Cu10Ga2□13]Ga32, i.e. a cubic primitive packing of 32 Ga atoms with Ta, Cu, and Ga in cubic voids and 13 vacancies. The pentagonal‐prismatic coordination of Ta and Cu can formally be obtained from the cubic primitive packing of Ga atoms by a 45° rotation of a part of the Ga8 cubes. There is a close similarity to the binary compounds Ta8Ga41 and Ta2–xGa5+x. The first one is also related to a CsCl‐like structure, the latter one contains rods of pentagonal prisms, which form the same columns. There are also relations to the ternaries V2Cu3Ga8 and V11Cu9Ga46, whose cubic structures are more or less complex variants of CsCl. 相似文献
150.
Synthesis and Characterization of GaIII,YIII, and LuIII Complexes with Etifenin and Analogues 下载免费PDF全文
Michel Pfeifer‐Leeg Gergely Szabó Zsolt Baranyai Tobias Niksch Wolfgang Weigand Martin Freesmeyer 《无机化学与普通化学杂志》2016,642(6):486-491
Complexes of etifenin ( 1a ), disofenin ( 1b ), and mebrofenin ( 1c ) with GaIII, YIII, and LuIII were synthesized and characterized by NMR spectroscopy and UV/Vis spectroscopy. Stability and protonation constants of the complexes of 1a were determined by potentiometry and distribution diagrams were calculated. It was shown that the YIII and LuIII species are most stable as bis chelates at higher pH, whereas the GaIII complex degrades at pH < 4.5. 相似文献