Substitution features in the isomorphous replacement series for metal-organic compounds (NbxTa1−x)4O2(OMe)14(ReO4)2, x=0.7, 0.5, 0.3—Single-source precursors of complex oxides with organized porosity

Trimetallic oxoalkoxide complexes (Nb_0.7Ta_0.3)₄O₂(OMe)₁₄(ReO₄)₂ (I), (Nb_0.3Ta_0.7)₄O₂(OMe)₁₄(ReO₄)₂ (II) and (Nb_0.5Ta_0.5)₄O₂(OMe)₁₄(ReO₄)₂ (III) were obtained by the interaction of rhenium heptoxide (VII) Re₂O₇ with niobium and tantalum alkoxides M₂(OMe)₁₀ (M=Nb, Ta) in toluene. The centrosymmetric molecules (I)-(III) can be considered as a product of condensation of two M₂(OMe)₉(OReO₃) molecules with the formation of two oxo-bridges. The specific feature of the structure is the uneven distribution of metal atoms in the crystallographic positions, where one symmetry-independent position, connected via μ-O with a perrhenate ReO₄⁻ group, is predominantly occupied by niobium atoms, while the other one connected via alkoxide groups has a higher tantalum content. The distribution of Nb and Ta in the structure is truly even only for compound III. The niobium and tantalum content is varied to a different extent for I (less) and for II (more), which is apparently due to small differences in the sizes of these two cations, resulting in preferences for packing of different molecules in the structures. Thermal decomposition of (Nb_1−xTa_x)₄O₂(OMe)₁₄(ReO₄)₂ (x=0.3, 0.5, 0.7) in air leads to the formation of crystalline species of solid solutions based on tantalum and niobium oxides displaying semi-ordered pores with the size of 100−250 nm. In the dry nitrogen atmosphere, the decomposition leads to the amorphous complex oxides containing rhenium, niobium and tantalum.     

Trichloro- and triisopropoxy-niobium(V) and tantalum(V) bis -( O,O ′-alkylene dithiophosphates): synthesis and characterization

Trichloro- and triisopropoxy-niobium(V) and tantalum(V) alkylene dithiophosphates, (M = Nb(V) or Ta(V); G =–CHMeCHMe–,–CMe₂CMe₂–,–CH₂CMe₂CH₂–,–CH₂CEt₂CH₂–or–CMe₂CH₂CHMe–and X = Cl or OPrⁱ) have been synthesized by reaction of metal(V) chloride, MCl₅, or triisopropoxymetal(V) dichloride, (PrⁱO)₃MCl₂, with the sodium salts of O,O′-alkylene dithiophosphoric acids, in 1 : 2 molar ratio in THF under anhydrous conditions. These pink-purple or light-yellow compounds are viscous, semi-solid or solid, hydrolyzable and soluble in common organic solvents. These compounds have been characterized by elemental analyses, molecular weight determinations and spectral studies like IR and heteronuclear NMR (¹H, ¹³C and ³¹P), which indicated a bidentate mode of chelation of dithio ligands, leading to a pentagonal bipyramidal geometry around the niobium(V) or tantalum(V) centers.     

钽在无水乙醇中的腐蚀

采用动电位极化、循环伏安、交流阻抗和扫描电镜等技术研究了钽在四乙基氯化铵（TEA）乙醇溶液中的腐蚀行为．在循环伏安曲线的扫描初期,电极表面因存在一薄层氧化物膜而使得电流密度缓慢增加．后来钝化膜因受到氯离子的攻击而被击穿,即点蚀．扫描电镜图很好地显示出蚀孔的生长过程．点蚀电位随着TEA浓度的增加而下降,随着水含量的增加而上升．在所研究的温度范围内,电化学反应的活化能为36kJ／mol．所有电极电位下的交流阻抗图谱都包含两个时间常数,钝化膜电阻和电荷传递电阻均随电极电位的增加而下降．     

Controlled deposition of covalently bonded tantalum oxide on carbon supports by solvent evaporation sol-gel process

A simple strategy for covalently attaching Ta₂O₅ particles onto functionalized graphitic carbon supports has been developed to fabricate hybrid nanocomposites. In this process, tantalum ethoxide was directly reacted with functional groups on the carbon surface to form covalent bonding, which caused the carbonyl stretches of the carbon supports to be blue-shifted to 50-70 cm⁻¹ after Ta₂O₅ particle deposition. Homogeneously deposited Ta₂O₅ particles on the carbon supports have been studied by X-ray diffraction (XRD), FT-IR spectroscopy, scanning electron microscopy (SEM), and transmission electron microscope (TEM).     

高能通量脉冲电子束作用下钽靶破坏初步研究

 使用Monte-Carlo程序MCNP在2维情况下模拟得到了高能通量脉冲电子束在钽金属靶中的能量沉积。根据能量沉积的模拟结果以及实验后靶上穿孔的大小和形貌,提出了电子束对不同结构钽金属靶破坏的物理机制。由于能量沉积的差异,1 mm实心靶中的热激波在一定时间内沿径向和轴向持续对靶材进行压缩,而在叠靶中这种压缩效果并不明显,因此实验后1 mm实心靶上穿孔的大小几乎是叠靶上的两倍。根据理论模型分析得到的靶材熔融喷射和层裂现象与实验结果相吻合。     

Niob- und Tantal-Komplexe des N-metallierten Hexamethylimidophosphorsäuretriamids und des Tris-tert-butyliminophosphorans

Niobium and Tantalum Complexes of N-Metalated Hexamethyl Imidophosphorus Acid Trisamide and Tris-tert-butyl Iminophosphorane Sterically most demanding phosphorane iminato ligands [N=PR₃]^– (R = ^tBu, NMe₂) with pronounced π-basic character are used for the stabilization of π-acidic d⁰ metal centers. In this respect the reaction of niobium and tantalum oxo chlorides MOCl₃ (M = Nb, Ta) with Me₃SiN=P(NMe₂)₃ leads to selective formation of (Me₃Si)₂O and [M{NP(NMe₂)₃}₂Cl₃] (M = Nb 1 , Ta 2 ). By reaction of the metal pentachlorides with the N-lithiated ligands the hitherto unknown tris-substituted derivatives [M(NPR₃)₃Cl₂] (M = Nb: R = ^tBu 3 , NMe₂ 4 ; M = Ta: R = ^tBu 5 , NMe₂ 6 ) are obtained. [Ta(NP^tBu₃)₃Cl₂] ( 5 ) was characterized by an X-ray crystal structure analysis. The tantalum center is trigonal-bipyramidally coordinated by three equatorial phosphorane iminato and two axial chloro ligands. The high temperature ³¹P-NMR spectrum of [Nb{NP(NMe₂)₃}₃Cl₂] ( 4 ) allows the observation of a decett, characterized by ²J(Nb–P) = 279 Hz.     

Organometallic Niobium and Tantalum Complexes with Primary Phosphine Ligands: Syntheses and Molecular Structures of [Cp*MCl4(PH2R)] (M = Nb,Ta; Cp* = C5Me5;R = But,Ad, Cy,Ph, 2, 4, 6‐Me3C6H2 (Mes))

The reaction of [Cp*MCl₄] (M = Nb, Ta; Cp* = C₅Me₅) with PH₂R in toluene at room temperature gives the primary phosphine complexes [Cp*MCl₄(PH₂R)] [Cp* = C₅Me₅; M = Nb: R = Bu^t ( 1a ), Ad ( 2a ), Cy ( 3a ), Ph ( 4a ), 2, 4, 6‐Me₃C₆H₂ (Mes) ( 5a ); M = Ta: R = Bu^t ( 1b ), Ad ( 2b ), Cy ( 3b ), Ph ( 4b ), Mes ( 5b )] in high yield. 1—5 were characterized spectroscopically (NMR, IR, MS) and by crystal structure determinations. The starting material [Cp*TaCl₄] is monomeric in the solid state, as shown by crystal structure determination.     

Preparation and Crystal Structure of Li4[TaN3]

The new lithium nitridotantalate(V), Li₄[TaN₃], was prepared by reaction of Li₁₅[CrN₄]₂N with the wall of a welded Ta ampoule in the presence of metallic Li at 1470 K. Li₄[TaN₃] forms colourless single crystals (platelets, space group Ibca, No. 73, a = 491.85(4) pm, b = 973.59(6) pm, c = 1415.0(1) pm, Z = 8, R1 = 0.0288). The crystal structure is described as Li₂O superstructure with ordered occupation of the tetrahedral sites by Li and Ta. The resulting arrangement leads to infinite chains [TaN₂N_2/2^4—] running along [100].     

Preparation,Crystal Structure,Physical Properties,and Electronic Band Structure of TlTaS3

TlTaS₃ was prepared by applying a sequence of two melting processes with mixtures of Tl₂S, Ta, and S having different molar metal to sulphur ratios. TlTaS₃ crystallises in space group Pnma with a = 9.228(3)Å, b = 3.5030(6)Å, c = 14.209(3)Å, V = 459.3(2)ų, Z = 4. The structure is closely related to the NH₄CdCl₃‐type. Characteristic features of the structure are chains of edge‐sharing [Ta(+5)S₄S_2/2]₂ double octahedra running along [010]. These columns are linked by Tl⁺ ions. The Tl⁺ ion is surrounded by eight S^2— anions to form a distorted bi‐capped trigonal prism. The Tl⁺ ions are shifted from the centre of the trigonal prism toward one of the rectangular faces. This is discussed in context with other isostructural compounds. TlTaS₃ is a semiconductor. The electronic structure is discussed on the base of band structure calculations performed within the framework of density functional theory.     

Determination of niobium(V) and tantalum(V) as 4-(2-pyridylazo)resorcinol–citrate ternary complexes in geological materials by ion-interaction reversed-phase high-performance liquid chromatography

A method for the simultaneous separation and determination of Nb(V) and Ta(V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and citrate was developed using ion-interaction reversed-phase high-performance liquid chromatography on a C₁₈ column. Method parameters, such as pre-column complex formation conditions and composition of the complexes were investigated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol–water (32:68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM citrate buffer at pH 6.5, with detection at 540 nm. A typical separation efficiency was 33 000 and 20 000 theoretical plates per metre for Nb(V) and Ta(V), respectively. The relative standard deviation of retention times for the Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0.28% and 1.36%, respectively. The detection limits (signal-to-noise ratio=3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtained for standard reference rock samples agreed well with certified values and results obtained by inductively coupled plasma MS.