- Triniobiumoctabromide, Nb3Br8, revisited
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A facile route to single crystals of Nb3Br8 by the reaction of NbBr5 with the wall of the niobium reaction vessel at 800 °C is reported. The crystal structure (a = 707.87(5), c = 3895.7(6) pm, R3m, Z = 6) was determined from diffractometer data; the crystal data are compared with those obtained from film data in 1966 which were of already high precision. Triangular {Nb3} clusters with Nb-Nb distances of 288.6(2) pm are surrounded by 13 bromide ligands which bridge them to double layers, {Nb3}(μ3-Br4)i 1/1(μ 2-Br1)i (3/2)·2(μ1-Br2) a-a 6/2(μ1-Br3)a-a-a 3/3 that are stacked to a 12R structure.
- Habermehl, Katja,Meyer, Gerd
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- Studies on interactions in the NbBr5-Nb system
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For studying the thermal disproportionation and interaction processes of niobium bromides in the NbBr5-Nb system thermoanalytical and tensimetric methods were employed. The study revealed that the reduction of niobium pentabromide by metallic n
- Vlaskina,Izmailovich,Tsirelnikov
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- The preparation and properties of niobium(IV) compounds. I. Some niobium(IV) halides and their pyridine adducts
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Reaction of NbBr5 and niobium metal in a sealed tube under a temperature gradient from 410 to 350° gave NbBr4 in good yields. However, an increase in the higher temperature from 410 to 450° was sufficient to eliminate NbBr4 as a product and cause deposition of a lower bromide. The halides NbCl4 and NbBr4 are isomorphous solids of orthorhombic structure and lattice constants a = 8.12, b = 8.88, c = 6.84 A?. and a = 8.60, b = 9.31, c = 7.19 A?., respectively; both solids are diamagnetic over the range -195 to 25°. Formation of the tetrahalodi-(pyridine)-niobium(IV) complexes resulted from the reactions of the pure tetrahalides (Cl, Br, I) with pyridine at room temperature; at elevated temperatures a second form of NbBr4(py)2 crystallized from pyridine. Evidence bearing on the structure of the pyridine adducts was obtained from conductance, spectral, and magnetic susceptibility measurements. The complexes are paramagnetic and exhibit moments much lower than the spin-only value for one magnetic electron; the spectra of solutions in pyridine show intense bands in the visible region which have been attributed to charge transfer transitions.
- McCarley, Robert E.,Torp, Bruce A.
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- Crystal structure and physical properties of RbNBr11
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RbNb4Br11 was obtained by a solid state reaction of niobium powder, NbBr5 and RbBr in a sealed niobium tube at 500 °C. It crystallizes in the orthorhombic space group Pmma with a = 1699.5(1), b = 726.7(1), c = 694.5(1) pm, F= 857.6(1)-106 pm3, Z = 2 and is isotypic with CsNb4Br11. Four niobium atoms build a cluster in the shape of a rhombus with bonding distances of 295 pm (Nb1-Nb2) and 304 pm (Nb2-Nb2), respectively. The structure consists of [{Nb4}Br 6iBr10/2a-a]- cluster complex anions that are interconnected by two common edges and two faces to the next cluster complexes, thus forming a 2D undulated layer structure. The Rb+ ion is coordinated by 12 Br- ions in the shape of an anticuboctahedron. Electronic structure calculations indicate the presence of a band gap of approximately 0.33 eV. This is experimentally confirmed by an electrical conductivity measurement revealing a slightly higher gap of 0.46 eV.
- Habermehl, Katja,Kleinke, Holger,Meyer, Gerd
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- 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
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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).
- Nowak, Izabela,Page, Elizabeth M.,Rice, David A.,Richardson, Alan D.,French, Richard J.,Hedberg, Kenneth,Ogden, J. Steven
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p. 1296 - 1305
(2008/10/08)
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- Scanning Tunneling and Atomic Force Microscopy Study of Layered Transition Metal Halides Nb3X8 (X=Cl, Br, I)
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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.
- Magonov, S. N.,Zoennchen, P.,Rotter, H.,Cantow, H.-J.,Thiele, G.,et al.
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p. 2495 - 2503
(2007/10/02)
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- Heavier Halides of Early Transition Elements by Halide-exchange Reactions. Crystal and Molecular Structure of2
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The decahalogenodimetalates of zirconium(IV) as their triphenylmethyl deivatives have been obtained by the reaction of M(BH4)4 with the appropriate Ph3CX or by addition of Ph3CX to MX4.The crystal and molecular structure of2 h
- Calderazzo, Fausto,Pallavicini, Piersandro,Pampaloni, Guido,Zanazzi, Pier Francesco
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p. 2743 - 2746
(2007/10/02)
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- β-NbBr5, a New Modification of Niobium Pentabromide
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While trying to react NbBr5 with sulfur in a closed tube, crystals of the new modification β-NbBr5 were obtained.Its X-ray diffraction patterns have sharp reflexions and diffuse streaks showing the presence of a one-dimensional disorder.From the sharp reflexions alone, a statistically averaged sub-structure results; it has the space group Ccmm and the lattice constants a0 = 644, b0 = 1867 and c0 = 615 pm.Taking into account the diffuse streaks, the true structure was deduced; its lattice constants are a = 2a0, c = c0, b indefinite due to the disorder. β-NbBr5 is isostructural to tantalum pentaiodide.It consists of layers of (NbBr5)2 molecules that are stacked with displacement faults in the direction of b.The bromine atoms have a hexagonal close-packing arrangement. - Keywords: Niobium Pentabromide, Crystal Structure, Stacking Faults
- Mueller, Ulrich,Klingelhoefer, Paul
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p. 559 - 561
(2007/10/02)
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- 93Nb nuclear quadrupole resonance in orthorhombic phase of niobium pentabromide
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The 93Nb NQR has been investigated in one phase of NbBr 5 which was identified to be orthorhombic by the X-ray analysis. The resonance frequencies have been measured between 4.2 K and 423 K, its melting point. The coupling constant showed a positive temperature dependence up to melting point. The temperature dependence of the coupling constant is compared between NbBr5 and NbCl5 from the view point of π-bond character.
- Okubo, Noriaki,Abe, Yoshihito
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p. 1347 - 1348
(2008/10/08)
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- Preparations, Properties, and Crystal and Molecular Structures of the Cyanomethane Adducts of Niobium(IV) Chloride and Di-μ-sulphido-bis
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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 .
- Benton, A. John,Drew, Michael G. B.,Hobson, Richard J.,Rice, David A.
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p. 1304 - 1309
(2007/10/02)
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- Reactivity of transition metal fluorides. III. Higher fluorides of vanadium, niobium, and tantalum
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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.
- Canterford,O'Donnell
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p. 1442 - 1446
(2008/10/08)
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