10026-12-7Relevant articles and documents
Reactivity of transition metal fluorides. III. Higher fluorides of vanadium, niobium, and tantalum
Canterford,O'Donnell
, p. 1442 - 1446 (1966)
A series of oxidation-reduction and halogen-exchange reactions has been used to compare the chemical reactivities of the pentafluorides of vanadium, niobium, and tantalum. Vanadium pentafluoride is extremely reactive and its reaction pattern with many reagents is extremely complex, depending largely on relative proportions of reagents and other experimental conditions. The pentafluorides of niobium and tantalum are very much less reactive than that of vanadium and are similar to each other. There is some evidence that of the two, the niobium compound is slightly more reactive. The reactivities of these three pentafluorides are discussed in terms of their physical properties and in relation to the higher fluorides of neighboring transition elements.
Chlorination of niobium and tantalum ore
Gonzalez,Gennari,Bohe?,Del C. Ruiz,Rivarola,Pasquevich
, p. 61 - 69 (1998)
The reaction of chlorine with columbite concentrate, a niobium and tantalum ore, was studied by thermogravimetry between 300° and 950°C. Nonisothermal and isothermal measurements were performed. Morphological evolution of solid reactants and elemental composition of particles were analyzed by SEM and EDXS, respectively. The growth of crystals, high in Ta and Nb content, was observed. The Ta content in remaining samples was greater as the chlorination temperature increased. A scheme of the reaction mechanism is proposed.
Electrochemical and spectroscopic studies of the chloro and oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts
Von Barner,Bjerrum
, p. 9847 - 9851 (2005)
The equilibrium constant for the chloro complex formation of Nb(V) NbCl6-?NbCl5+Cl- (i) in NaCl-AlCl3 melts at 175°C was found to be pKi = 2.86(5). The oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl 3 melts at 175°C could be explained by the following equilibria: MOCl4-?MOCl3+Cl- (ii) MOCl 3?MOCl2++Cl- (iii) where M = Nb and Ta. The equilibrium constants determined by potentiometric measurements with chlorine-chloride electrodes were, for M = Nb, pKii, = 2.21(4) and pKiii = 3.95(5) and, for M = Ta, pKii = 2.743(15) and pKiii = 4.521(13). NbCl6- has two bands in the UV-vis region, a strong one at 34.7 × 103 cm-1 and a weaker one at 41.6 × 103 cm-1. The MOCl 4- complexes showed in the case of Nb(V) absorption bands at 32.7 and 42.9 × 103 cm-1 and in the case of Ta(V) at 38.6 and 48.1 × 103 cm-1.
Scanning Tunneling and Atomic Force Microscopy Study of Layered Transition Metal Halides Nb3X8 (X=Cl, Br, I)
Magonov, S. N.,Zoennchen, P.,Rotter, H.,Cantow, H.-J.,Thiele, G.,et al.
, p. 2495 - 2503 (1993)
Niobium halides Nb3X8 (X=Cl, Br, I) are made up of layers of composition Nb3X8, and the two surfaces (A and B) of their individual Nb3X8 layers are not equivalent an atomic corrugations.The surfaces of these halides were examined by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) to obtain atomic resolution images.For a given surfaces, AFM images differ significantly from STM images, and the resolution of the STM images depends on the tunneling conditions.The observed AFM and STM images were analyzed by calculating the total electron density distribution, ρ(rO), and the partial electron density distribution, ρ(rO, ef), for the two surfaces of single Nb3X8 (X=Cl, Br, I) layers.Our work shows that the AFM and STM images are well dscribed by the ρ(rO) and ρ(rO, ef) plots, respectively.A combined use of AFM and STM is useful in characterizing the surfaces of layered materials, and calculations of ρ(rO) and ρ(rO, ef) plots are indispensable in interpreting their AFM and STM images.
Preparations, Properties, and Crystal and Molecular Structures of the Cyanomethane Adducts of Niobium(IV) Chloride and Di-μ-sulphido-bis
Benton, A. John,Drew, Michael G. B.,Hobson, Richard J.,Rice, David A.
, p. 1304 - 1309 (1981)
The cyanomethane adduct of NbCl4 analyses for NbCl4*3CH3CN (1).A crystal-structure determination of this species shows that it contains cis octahedral and a solvent CH3CN molecule.The unique bond lengths are Nb-N 2.220(13) Angstroem and Nb-Cl 2.328(2),2.343(6), and 2.349(4) Angstroem.The crystals of (1) are orthorhombic with unit-cell dimensions a=10.437(11), b=13.883(12), c=9.828(9) Angstroem, Z=4, and space group Pnma.A total of 729 reflections above background have been collected on a diffractometer and refined to R 0.051.When the cyanomethane adducts of NbX4 (X=Cl or Br) are treated with Sb2S3 in cyanomethane, adducts of NbX2S (X=Cl or Br) are formed.The products contain 2> in which there is a ring.The crystal structures of two compounds, (2) and (3), containing the 2> dimeric unit have been determined.In (2) there are two molecules of occluded CH3CN for each dimer while (3) has one.Both (2) and (3) are triclinic with space group P, with (2) having a=9.031(7), b=9.367(6), c=8.360(8) Angstroem, α=108.72(9), β=94.93(7), γ=105.70(8) degree, Z=1 and (3) having a=14.965(18), b=8.838(17), c=9.543(23) Angstroem, α=112.42(18), β=84.39(28), γ=103.65(21) degree, z=2.For (2), 1434, and for (3), 1530, independent reflections above background have been collected on a diffractometer and refined to R 0.056 and 0.050 respectively.The dimer configurations in (2) and (3) are identical.The niobium atoms are in a pseudo-octahedral enviroment consisting of two cis sulphur, two trans chlorine , and two cis nitrogen atoms .In addition, in each dimer there is a Nb-Nb single bond .
Chalcogenide-halides of niobium (V). 1. Gas-phase structures of NbOBr3, NbSBr3, and NbSCl3. 2. Matrix infrared spectra and vibrational force fields of NbOBr3, NbSBr3, NbSCl3, and NbOCl3
Nowak, Izabela,Page, Elizabeth M.,Rice, David A.,Richardson, Alan D.,French, Richard J.,Hedberg, Kenneth,Ogden, J. Steven
, p. 1296 - 1305 (2003)
The molecular structures of NbOBr3, NbSCl3, and NbSBr3 have been determined by gas-phase electron diffraction (GED) at nozzle-tip temperatures of 250 °C, taking into account the possible presence of NbOCl3 as a contaminant in the NbSCl3 sample and NbOBr3 in the NbSBr3 sample. The experimental data are consistent with trigonal-pyramidal molecules having C3v symmetry. Infrared spectra of molecules trapped in argon or nitrogen matrices were recorded and exhibit the characteristic fundamental stretching modes for C3v species. Well resolved isotopic fine structure (35Cl and 37Cl) was observed for NbSCl3, and for NbOCl3 which occurred as an impurity in the NbSCl3 spectra. Quantum mechanical calculations of the structures and vibrational frequencies of the four YNbX3 molecules (Y = O, S; X = Cl, Br) were carried out at several levels of theory, most importantly B3LYP DFT with either the Stuttgart RSC ECP or Hay-Wadt (n + 1) ECP VDZ basis set for Nb and the 6-311G* basis set for the nonmetal atoms. Theoretical values for the bond lengths are 0.01-0.04 A longer than the experimental ones of type ra, in accord with general experience, but the bond angles with theoretical minus experimental differences of only 1.0-1.5° are notably accurate. Symmetrized force fields were also calculated. The experimental bond lengths (rg/A) and angles (∠α/deg) with estimated 2σ uncertainties from GED are as follows. NbOBr3: r(Nb=O) = 1.694(7), r(Nb - Br) = 2.429(2), ∠(O=Nb - Br) = 107.3(5), ∠(Br - Nb - Br) = 111.5(5). NbSBr3: r(Nb=S) = 2.134(10) r(Nb - Br) = 2.408(4), ∠(S=Nb - Br) = 106.6(7), ∠ (Br - Nb - Br) = 112.2(6). NbSCl3: r(Nb=S) = 2.120(10), r(Nb - Cl) = 2.271(6), ∠(S=Nb - Cl) = 107.8(12), ∠(Cl - Nb - Cl) = 111.1(11).
Chemistry of polynuclear metal halides. II. Preparation of polynuclear niobium chloride and bromide
Fleming, Peter B.,Mueller, Leta A.,McCarley, Robert E.
, p. 1 - 4 (1967)
Improved preparations leading to the compounds Nb6X14·8H2O (X = Cl, Br) are described. High yields of Nb6Cl122+ were obtained by the high-temperature reaction of KCl and Nb3Cl8 which proceeds via 14KCl + 5Nb3Cl8 = 2K4Nb6Cl18 + 3K2-NbCl6. Extraction of this reaction mixture with water provides a convenient route to Nb6Cl14·8H2O. The attempted formation of Nb6Cl14 via direct reduction of NbCl5 with aluminum was unsuccessful. However, aluminum reduction of NbBr5 provided an unidentified anhydrous product from which yields of up to 35% Nb6Br122+ were extracted. Equilibration reactions involving niobium and Nb3Br8 at temperatures up to 975° gave no evidence for phases having Br: Nb 6Cl122+ and Nb6Br122+ are given. Copyright 1967 by the American Chemical Society.
Model-free kinetics applied to regeneration of coked alumina
Fernandes Jr.,Araújo,Madruga,Nicolini
, p. 63 - 69 (2002)
Thermogravimetry is proposed for studying the alumina catalyst regeneration deactivated by coke, after being used in the transformation of styrene in a fixed bed continuous flow reactor. The model-free kinetic approach has been applied to data for thermal oxidation of carbonaceous deposits on the catalyst. The activation energy (E) was calculated as a function of conversion (α) and temperature (T), by using Vyazovkin model-free kinetic method, allowing to estimate time required to remove coke for a given temperature.
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
Schleifer, Michaela,Busch, Jochen,Albert, Barbara,Gruehn, Reginald
, p. 2299 - 2306 (2008/10/08)
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) A, c = 19.86(6) A). 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.
Process for the preparation of metal nitride coatings from single source precursors and precursors suitable therefor
-
, (2008/06/13)
Metal nitride coatings are deposited effectively by the decomposition of single source metal imido-amido-amine precursors prepared by the reaction of a pentavalent metal halide with a primary amine or hydrazine. With hydrazine-derived precursors, TaN coatings may be deposited at temperatures as low as 400 degrees Celcius or lower.
