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21.
Blanka Kubikova Miroslav Boca Marcelle Gaune-Escard 《Monatshefte für Chemie / Chemical Monthly》2008,139(6):587-590
The phase equilibria in the K2TaF7–TaF5 binary system were determined up to x
TaF5 = 0.5 by means of differential scanning calorimetry. XRD diffraction analysis of solidified mixtures was performed. Besides
the K2TaF7 and KTaF6 phases, the presence of a third phase was observed, as well. It was suggested that the last phase melts incongruently.
Correspondence: B. Kubikova, Institute of Inorganic Chemistry SAS, Dúbravská cesta 9, Bratislava, 845 36, Slovakia. 相似文献
22.
Christoph Riesinger Prof. Dr. Fabian Dielmann Robert Szlosek Dr. Alexander V. Virovets Prof. Dr. Manfred Scheer 《Angewandte Chemie (International ed. in English)》2023,62(16):e202218828
The thermolysis of Cp′′′Ta(CO)4 with white phosphorus (P4) gives access to [{Cp′′′Ta}2(μ,η2 : 2 : 2 : 2 : 1 : 1-P8)] ( A ), representing the first complex containing a cyclooctatetraene-like (COT) cyclo-P8 ligand. While ring sizes of n >6 have remained elusive for cyclo-Pn structural motifs, the choice of the transition metal, co-ligand and reaction conditions allowed the isolation of A . Reactivity investigations reveal its versatile coordination behaviour as well as its redox properties. Oxidation leads to dimerization to afford [{Cp′′′Ta}4(μ4,η2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1-P16)][TEF]2 ( 4 , TEF=[Al(OC{CF3}3)4]−). Reduction, however, leads to the fission of one P−P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand]2[{Cp′′′Ta}4(μ4,η2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1-P16)] ( 5 ), which features an unprecedented chain-type P16 ligand. Lastly, A serves as a P2 synthon, via ring contraction to the triple-decker complex [{Cp′′′Ta}2(μ,η6 : 6-P6)] ( B ). 相似文献
23.
建立了用电感耦合等离子体质谱仪(ICP-MS)测定高纯氧化钽中28种痕量杂质元素的方法。讨论了质谱干扰及接口效应,采用标准加入法消除基体效应。各元素的方法检出限为0.001~0.1μg/g,回收率为90%~115%,方法适用于纯度为99.999%的高纯氧化钽中痕量杂质元素的测定。 相似文献
24.
人体脏器中钼的石墨炉原子吸收测定方法的研究 总被引:2,自引:0,他引:2
本文讨论了用衬钽石管测定人体脏器中钼的方法。初钽管完全消除了形成稳定碳化物的影响,灵敏度较用普通石墨炉管提高约84倍,较用热解石墨管提高了一个数量级,完全消除 记忆效应,减少了钠、钾、铁等共存元素的干扰.方法简单、准确、快速。 相似文献
25.
On Polychalcogenides of Thallium with M2Q11 Groups as a Structural Building Block. I Preparation, Properties, X‐ray Diffractometry, and Spectroscopic Investigations of Tl4Nb2S11 and Tl4Ta2S11 The new ternary compounds Tl4Nb2S11 and Tl4Ta2S11 were prepared using Thallium polysulfide melts. Tl4M2S11 crystallises isotypically to K4Nb2S8.9Se2.1 in the triclinic space group P 1 with a = 7.806(2) Å, b = 8.866(2) Å, c = 13.121(3) Å, α = 72.72(2)°, β = 88.80(3)°, and γ = 85.86(2)° for M = Nb and a = 7.837(1) Å, b = 8.902(1) Å, c = 13.176(1) Å, α = 72.69(1)°, β = 88.74(1)°, and γ = 85.67(1)° for M = Ta. The interatomic distances as well as angles within the [M2S11]4– anions are similar to those of the previously reported data for analogous alkali metal polysulfides. Significant differences between Tl4M2S11 and A4M2S11 (A = K, Rb, Cs) are obvious for the shape of the polyhedra around the electropositive elements. The two title compounds melt congruently at 732 K (M = Nb) and 729 K (M = Ta). The optical band gaps were estimated as 1.26 eV for Tl4Nb2S11 and as 1.80 eV for the Tantalum compound. 相似文献
26.
Structural Investigations on the Oxidenitrides SrTaO2N, CaTaO2N and LaTaON2 by Neutron and X‐ray Powder Diffraction The crystal structures of the perovskite related oxidenitrides SrTaO2N, LaTaON2 and CaTaO2N have been determined with special regard to the structures of the respective anionic partial structure. The structure refinements were performed by individual Rietveld analyses of both X‐ray and neutron powder diffractograms and in addition by joint refinements in order to confirm the results. Both refinement methods yield consistent structure solutions. At least the first two compounds have fully ordered anionic sublattices. The crystal structure of SrTaO2N has been solved in the space group I4/mcm (a = 5.7049(3) Å, c = 8.0499(5) Å, Rp = 0.0706, Rwp = 0.0904, reflections: 70 (neutrons)/36 (X‐ray), R(F2)(n) = 0.147, R(F2)(X) = 0.0952), with an ordered anionic partial structure. LaTaON2 crystallizes monoclinic (C2/m, a = 8.0922(3) Å, b = 8.0603(2) Å, c = 5.7118(2) Å, β = 134.815(1)°, Rp = 0.0592, Rwp = 0.0766, reflections: 235(n)/113(X), R(F2)(n) = 0.0944, R(F2)(X) = 0.165) and also shows a totally ordered distribution of the anions. In the case of CaTaO2N (Pnma, a = 5.6239(3) Å, b = 7.8954(4) Å, c = 5.5473(3) Å, Rp = 0.0503, Rwp = 0.0656, reflections 206(n)/110(X), R(F2)(n) = 0.0985, R(F2)(X) = 0.0405) slightly unbalanced displacement parameters (neutron data, ordered O/N distribution model) hint at a partial exchange of oxygen and nitrogen. 相似文献
27.
Synthesis and Crystal Structure of U2Ta6O19, a New Compound with “Jahnberg‐Structure” and a Note to the First Oxide Chlorides in the Systems Th/Nb/O/Cl and Th/Zr(Hf)/Nb/O/Cl Black crystals of U2Ta6O19 with hexagonal shape were obtained (at T1) by chemical transport using HCl (p (HCl, 298 K) = 1 atm; silica tube) as transport agent in a temperature gradient (T2 → T1; 1000 °C → 950 °C) and using a mixture of UO2, Ta2O5, and HfO2 (or ZrO2) (1 : 2 : 2) as starting materials (at T2). For the structure determination the best result was achieved in space group P63/mcm (No. 193, a = 6.26(2) Å, c = 19.86(6) Å). U2Ta6O19 is isotypical to Th2Ta6O19. In the crystal structure each uranium atom is surrounded by oxygen atoms like a bi‐capped trigonal antiprism and tantalum atoms like a pentagonal bipyramid (CN = 7). Like the “Jahnberg Structures” both coordination polyhedra arrange themselves in separate layers (U–O‐polyhedra, in o‐, Ta–O‐polyhedra in p‐layers) so that in the direction of the c‐axis the sequence of layers is p‐p‐o. Using chemical transport it was possible to prepare the compounds Th12Nb16O63Cl2 and Th8M4Nb16O63Cl2 (M = Zr, Hf), which are the first quaternary and quinquinary examples in these systems. They crystallize isotypically. 相似文献
28.
The Metal‐rich Layer Structure of Ta6STe3 Ta6S1+xTe3–x was prepared from an appropriate mixture of 2 H–Ta1.3S2, TaTe2, and Ta in a fused tantalum tube at 1273 K within 3 d. The results of a X‐ray single crystal structure analysis for a phase near the Te‐rich limit of the homogeneity range are reported. Ta6S1.00Te3.00(1) crystallizes in the triclinic space group P1, a = 993.14(8) pm, b = 1032.18(8) pm, c = 1378.78(11) pm, α = 79.32(1)°, β = 81.36(1)°, γ = 85.74(1)°, Z = 6, Pearson symbol aP60, 6048 Io > 2σ (Io), 286 variables, wR2 = 0.067. The metal‐rich layer structure of Ta6STe3 comprises distorted icosahedral Ta13 clusters and related deltahedral cluster fragments complemented by chalcogen atoms. The centred clusters consist of 11, 12, 13, 14, or 16 atoms. They interpenetrate into lamellae in which the tantalum and chalcogen atoms are spatially segregated according to [Q–Ta3–Q]. The signature of the structure is a lenticular heptagonal antiprismatic Ta30 cluster which seems to be excised from the pentagonal antiprismatic columnar structure of Ta6S. The Ta30 clusters and distorted icosahedral Ta13 clusters are connected and fused into puckered layers. The rest of the tantalum valences are used for heteronuclear bonding. The chalcogen atoms having three to six next tantalum atoms coat the corrugated, tetrahedrally close‐packed layers. Ta6STe3 is a moderate metallic conductor (ρ293 K = 3 × 10–4 Ωcm) exhibiting typical temperature independent paramagnetic properties. 相似文献
29.
Matthias Conrad Frank Krumeich Bernd Harbrecht 《Angewandte Chemie (International ed. in English)》1998,37(10):1383-1386
Diffractograms with twelvefold rotational symmetry (depicted on the right) were obtained from the first quasicrystalline chalcogenide Ta1.6Te. This compound was prepared on a preparative scale by the reduction of TaTe2 with tantalum below 1870 K. This tantalum-rich telluride, which is the first stable dodecagonal phase, has enabled an in-depth investigation of this unusual state of ordering. 相似文献
30.