Crystal Structure and Electron Density Distribution in Niobium Carbide

In this paper the bonding properties, e. g. the charge distribution between the atoms and the deformation of niobium carbide densities have been studied. The crystal studied had the composition NbC_0.98. Careful and redundant data collection (74 unique reflections out of 2087 reflections measured) gave the basis for a detailed study. IAM models (independent atom model), high order and multipole refinements were made resulting in R values of R = 0.4% and R = 0.07%. In the corresponding deformation density maps electron accumulations between the niobium atoms were detected, but no bonding to the carbon atoms.     

NbCl5 a multifunctional reagent for the synthesis of new halogenated aminoquinoline compounds through innovative one-pot reaction and the acidochromism effect

This paper describes an original one-pot way to synthesize nine new halogenated aminoquinoline derivatives using reactions conducted by niobium pentachloride. Subsequently, we describe an efficient and selective reduction reaction of nitroquinolines using niobium pentachloride and zinc, producing important compounds in the organic synthesis.The results showed that it is an important tool to synthesize these compounds, besides being time- and resources-saving and generating good yields. A quick study of acidochromism was performed.     

Isolation and single crystal study of [Nb2(μ-OMe)2(OiPr)8]. Can alcohol interchange provide the homoleptic niobium isopropoxide?

Niobium isopropoxide, Nb(OⁱPr)₅, is an attractive precursor of simple and complex niobium oxides in sol-gel technology. This compound cannot, unfortunately, be obtained by alcohol interchange starting from linear chain homologues such as Nb(OMe)₅ or Nb(OEt)₅. The equilibrium in the latter reaction favours formation of mixed-ligand complexes, [Nb₂(OR)₂(OⁱPr)₈], R = Me, Et. In particular, [Nb₂(OMe)₂(OPrⁱ)₈] (1) has been isolated in high yield from repeated treatment of Nb₂(OMe)₁₀ with excess of isopropanol. The X-ray single crystal study reveals a dinuclear structure containing a pair of edge-sharing octahedra with methoxide ligands in the bridging position. Infrared (IR) and mass spectroscopy (MS) studies confirmed the incomplete ligand substitution. The ¹H-NMR spectra suggest equilibrium between different molecular forms in solution. Solvothermal interaction of 1 with La chips in toluene/isopropanol media results in formation of a mixture of LaNb₂(OⁱPr)₁₃ and La₂Nb₄(μ₄−O)₄(OH)₂(μ−OⁱPr)₈(OⁱPr)₈ (2). Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorised users.     

A new molecular precursor route for the synthesis of Bi-Y, Y-Nb and Bi-doped Y-Nb oxides at moderate temperatures

Yttrium-based multimetallic oxides containing bismuth and/or niobium were prepared by a method starting from pre-isolated stable water-soluble precursors which are complexes with the ethylenediaminetetraacetate ligand (edta). The cubic Bi_1−xY_xO_1.5 (x=0.22, 0.25 and 0.3) and Y₃NbO₇ oxides were obtained in a pure form in a range of moderate temperatures (600-650 °C). This preparation method also allowed to stabilize at room temperature, without quenching, the tetragonal YNbO₄ oxide in a distorted form (T′-phase) by calcining the precursor at 800 °C. When heated up to 1000 °C, this metastable T′-phase transforms into the metastable “high-temperature” T oxide, which converts on cooling down to room temperature into the thermodynamically stable monoclinic M oxide. Doping the YNbO₄ oxide with Bi³⁺ cations (0.5% and 1% Bi with respect to total Bi+Y amount) led at 800 °C to a mixture of the T′-phase and the thermodynamically stable monoclinic one. At 900 °C, the almost pure monoclinic structure was obtained.     

Nb-Ta, Nb-Mo and Nb-V oxides prepared from hybrid organic-inorganic precursors

New hybrid organic-inorganic materials based on group 5 elements and a well-defined polymeric matrix have been prepared and used as precursors for Nb-Ta and Nb-Mo mixed oxides. In this non-conventional but easily accessible route to multimetallic oxides, a copolymer of N,N-diallyl-N-hexylamine and maleic acid was synthesised and used as matrix to stabilise inorganic species generated in solution from (NH₄)₆Mo₇O₂₄·4H₂O, NH₄VO₃, (gu)₃[Nb(O₂)₄] and (gu)₃[Ta(O₂)₄]. Solid-state studies indicate that the homogeneity of the blends can be kept up to about 0.5 mol Nb^V and Ta^V and 0.25 mol V^V per mol of repeat units of the copolymer. The calcination conditions of these homogeneous hybrid precursors were optimised to produce Nb-Mo, Nb-Ta and Nb-V oxides. While the thermal treatment of the Nb-V hybrid blends led only to a mixture of different phases, the characterisation of the final phases by X-ray diffraction (XRD) proved the formation of pure Nb₂Mo₃O₁₄ and showed that Nb-Ta oxides could be synthesised as single phases corresponding to a continuous series of solid solutions.     

偶氮氯膦mA-铌与牛血清白蛋白结合反应及其应用

用分光光度法研究了偶氮氯膦-mA-铌配合物与牛血清白蛋白(BSA)结合反应体系.在pH3.0的磷酸氢二钠-柠檬酸缓冲溶液(Mcllvaine)中,随着BSA量的增加,偶氮氯膦mA-铌配合物在542 nm波长处吸收峰也随着减小.据此建立了以偶氮氯膦mA-铌配合物为光谱探针,光度法测定蛋白质的新方法.牛血清白蛋白量在0～60 mg/L范围内与体系的褪色程度呈良好的线性关系,其相关系数为r=0.9996,摩尔吸光系数为ε542=3.3×105 L·mol-1·cm-1.方法应用于人血清蛋白的测定.     

Synthesen und Kristallstrukturen neuer chalkogenido‐verbrückter Niob‐Kupfer‐Cluster

Syntheses and Crystal Structures of Novel Chalcogenido‐bridged Niobium Copper Clusters In the presence of tertiary phosphines, the reaction of NbCl₅ and Copper(I) salts with Se(SiMe₃)₂ (E = S, Se) affords the new chalcogenido‐bridged niobium‐copper cluster compounds ( 1 ) and [NbCu₄Se₄Cl (PPh₃)₄] ( 2 ). Using E(R)SiMe₃ (E = S, Se, R = Ph, ⁿPr) instead of the bisilylated selenium species leads to the compounds [NbCu₂(SPh)₆(PMe₃)₂] ( 3 ), [NbCu₂(SPh)₆(PⁿPr₃)₂] ( 4 ), [NbCu₂(SePh)₆(PMe₃)₂] ( 5 ), [NbCu₂(SePh)₆(PⁿPr₃)₂] ( 6 ), [NbCu₂(SePh)₆(PⁱPr₃)₂] ( 7 ), [NbCu₂(SePh)₆(P^tBu₃)₂] ( 8 ), [NbCu₂(SePh)₆(PⁱPr₂Me)₂] ( 9 ), [NbCu₂(SePh)₆(PPhEt₂)₂] ( 10 ), [Nb₂Cu₂(SⁿPr)₈(PⁿPr₃)₂Cl₂] ( 11 ) and [Nb₂Cu₆(SⁿPr)₁₂(PⁱPr₃)₂Cl₄]·2 CH₃CN ( 12 ·2 CH₃CN). By reacting Cu^I salts and NbCl₅ with the monosilylated selenides Se(^tBu)SiMe₃ and Se(ⁱPr)SiMe₃ which have a weak Se–C bond the products [Nb₂Cu₆Se₆(PⁱPr₃)₆Cl₄] ( 13 ), [Nb₂Cu₄Se₂(SeⁱPr)₆(PⁿPr₃)₄Cl₂] ( 14 ) and [Nb₂Cu₆Se₂(SeⁱPr)₁₀(PEt₂Me)₂Cl₂]·DME ( 15 ) are formed which contain selenide as well as alkylselenolate ligands. The molecular structures of all of these new compounds were determined by single crystal X‐ray diffraction measurements.     

An extended open framework based on disordered [Nb6Cl9O3(CN)6] cluster units: Synthesis and crystal structure of Cs3Mn[Nb6Cl9O3(CN)6]0.6H2O

The synthesis and crystal structure of Cs₃Mn[Nb₆Cl₉O₃(CN)₆]0.6H₂O are described in this work. It crystallizes in the cubic system (space group Fm-3m; a=15.708(5) Å) and is characterized by a static orientational disorder of the [Nb₆Cl₉O₃(CN)₆]⁵⁻ cluster units. It results in a framework structurally related to that encountered in the well known Prussian Blue family prepared for different hexacyanometallates. The charge of the framework is compensated by cesium cations that are located in the tetrahedral cavities of the c.f.c. lattice of units along with water molecules. We will evidence the features that act in the crystallization of solid state compounds built up from ordered or disordered units as well as the influence of orientational disorder on interatomic distances obtained from single-crystal X-ray diffraction investigations.     

用冠醚和硫氰酸钾萃取光度法测定钢铁中微量铌

报道了用双(苯并-18-冠-6)和硫氰酸钾试剂萃取光度测定钢铁中的微量铌,方法的选择性好,灵敏度高,ε_(400nm)=3.85×10~4L·mol~(-1)·cm~(-1),铌在1～20μg/25ml范围内有较好的线性关系,线性回归方程A=0.936C(mg·ml~(-1))-1.425×10~(-3)。     

Deactivation of Pd particles supported on Nb2O5/Cu3Au(1 0 0): SFG and TPD studies from UHV to 100 mbar

Structural changes that occur on Pd-Nb₂O₅/Cu₃Au(1 0 0) model catalysts upon thermal annealing were followed by sum frequency generation (SFG) and temperature-programmed desorption (TPD) using CO as probe molecule. SFG experiments were performed both under ultrahigh vacuum and mbar pressure. Heating the catalyst to temperatures above 300 K lead to an irreversible 50% decrease in the CO adsorption capacity and modified the remaining adsorption sites. Alterations of the phase between resonant and non-resonant SFG signals upon annealing indicate a change in the electronic structure of the surface, which excludes Pd sintering or migration of Nb₂O₅ over Pd particles to cause the observed effect and rather suggests the formation of “mixed Pd-NbO_x” sites. The same changes in surface properties also occur during CO hydrogenation at 1 bar and high temperature, pointing to an involvement of “mixed Pd-NbO_x” sites in catalytic reactions.