Progress in Niobium and Tantalum coordination chemistry
About: This article is published in Coordination Chemistry Reviews.The article was published on 1992-03-01. It has received 25 citations till now. The article focuses on the topics: Coordination complex & Tantalum.
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TL;DR: Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered in this paper.
320 citations
TL;DR: These measurements reveal that the (93)Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the Nb(V) positions, with C(Q) values in the 0 to >80 MHz range being measured; similarly, the delta(iso) and Omega values are also sensitive to structural disposition.
Abstract: A variable B0 field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high-precision measurement of 93Nb NMR interaction parameters such as the isotropic chemical shift (δiso), quadrupole coupling constant and asymmetry parameter (CQ and ηQ), chemical shift span/anisotropy and skew/asymmetry (Ω/Δδ and κ/ηδ) and Euler angles (α, β, γ) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR-CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from NbV in most oxo environments, this study emphasises that a thorough variable B0 approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (−1/2↔+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these 93Nb broadline data. These measurements reveal that the 93Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the NbV positions, with CQ values in the 0 to >80 MHz range being measured; similarly, the δiso (covering an approximately 250 ppm range) and Ω values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the NbO bond angles and distances defining the immediate NbV oxo environment is complicated by longer-range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the 93Nb NMR interaction parameters generated here are the all-electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR-CASTEP DFT approaches, which account for the short- and long-range symmetries, periodicities and interaction-potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure.
55 citations
TL;DR: In this article, the precursors to the dialkyl carbamates of niobium and tantalum have been obtained, which are suggested to be dinuclear with bridging carbamato groups, a metal-metal bond and axially co-ordinated hexamethylbenzene.
Abstract: The mononuclear compounds M(O2CNR2)n(M = Nb or Ta, R = Et, n= 5; M = Nb, R = Et or Pri, n= 4) have been prepared by treating the corresponding metal chlorides or their adducts, i.e.[NbCl4(thf)2](thf = tetrahydrofuran), with CO2–NHR2 in toluene. The molecular structures of Ta(O2CNEt2)5 and Nb(O2CNEt2)4 have been solved by X-ray diffraction methods. The tantalum atom is eight-co-ordinated, being surrounded by three bi- and two mono-dentate diethylcarbamato groups, in a slightly distorted square-antiprismatic arrangement. The niobium compound consists of mononuclear units, where the niobium atom is dodecahedrally co-ordinated to eight oxygen atoms of four bidentate diethylcarbamate ligands. The reaction of [NbCl3(dme)](dme = 1,2-dimethoxyethane) with CO2–NHR2(R = Et or Pri) gave the corresponding dialkylcarbamates; on the basis of spectroscopic and magnetic data these niobium(III) derivatives are suggested to be dinuclear with bridging and terminal carbamato groups. Improved yields of [M2(η6-C6Me6)2Cl4](M = Nb or Ta), which are the precursors to the dialkylcarbamates of niobium(II) and tantalum(II), have been obtained. The [M2(η6-C6Me6)2Cl4]–CO2–NHPr2i system (M = Nb or Ta) in toluene gave metal(II) dialkylcarbamato complexes of analytical composition M(η6-C6Me6)(O2CNPr2i)2: these substantially diamagnetic compounds are suggested to be dinuclear with bridging carbamato groups, a metal–metal bond and axially co-ordinated hexamethylbenzene.
28 citations
TL;DR: In this paper, the authors used the rotating disk electrode methodology for characterization of the ORR and high-angle annular dark-field scanning transmission electron microscopy with high-resolution energy-dispersive X-ray spectroscopy (EDS) capabilities.
Abstract: The Pt activity for the oxygen reduction reaction (ORR) is improved when Pt nanoparticles are supported on nanoscale layers of tantalum oxyphosphate (nominally, TaOPO4) on Vulcan carbon (VC) and heated at high temperature (660 °C) in reducing conditions. We attempt to explain the increased activity of the Pt-TaOPO4/VC “HT” by comparison to other less-active electrocatalysts comprising Pt on tantalum oxide (Pt-Ta2O5/VC) and Pt-TaOPO4/VC heated to 200 °C in air. Our toolbox for this analysis contains the rotating disk electrode methodology for characterization of the ORR and high-angle annular dark-field scanning transmission electron microscopy with high-resolution energy-dispersive X-ray spectroscopy (EDS) capabilities. The adsorption of molecular species on the Pt and Ta is determined from the Δμ XANES (X-ray absorption near-edge structure) adsorbate isolation technique of X-ray absorption spectroscopy (XAS) data for electrocatalsyts in situ, whereby H and OH adsorption products from water activation can...
24 citations
TL;DR: H2SO4 was found to be the best candidate for Zr leaching from the eudialyte as mentioned in this paper, and the resulting sulfuric leach solution consisted of Zr(IV, Nb(V), Hf(IV), Al(III), and Fe(III).
Abstract: H2SO4 was ensured to be the best candidate for Zr leaching from the eudialyte. The resulting sulfuric leach solution consisted of Zr(IV), Nb(V), Hf(IV), Al(III), and Fe(III). It was found that ordi ...
17 citations
Cites background from "Progress in Niobium and Tantalum co..."
...According to the literature [25,26], basic zirconium sulfate can be obtained when zirconium chloride solution is mixed with sulfuric acid solution at a set temperature (60–90 C) and pH (1....
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References
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TL;DR: The ternary chalcogenides Ta/sub 2/NiS/sub 5/ (D/ sub 2h//sup 17/Cmcm; a = 3.415 (1), b = 12.496 (1) and c = 15.641 (4) A;..beta.. = 90.097 (4), c =15.146 (3), c=15.637 (3).
Abstract: Two new ternary chalcogenides have been prepared and characterized. Both Ta/sub 2/NiS/sub 5/ (D/sub 2h//sup 17/-Cmcm; a = 3.415 (1), b = 12.146 (3), c = 15.097 (4) A) and Ta/sub 2/NiSe/sub 5/ (C/sub 2h//sup 6/-C2/c; a = 3.496 (1), b = 12.829 (3), c = 15,641 (4) A; ..beta.. = 90.53 (1)/sup 0/) crystallize as layered structures with four formula units per cell. These layers contain octahedral tantalum atoms and tetrahedral nickel atoms each coordinated by chalcogen atoms. These polyhedra join via shared edges to form zigzag chains along the c axis. Electrical conductivity and magnetic susceptibility measurements show these materials to be diamagnetic semiconductors. The description of the structures as Ta/sup 4 +/Ni/sup 2 +/Q/sup 2 -/ (Q = S, Se) with pairing of nickel and tantalum electrons is consistent with these physical properties. 21 references, 4 figures, 6 tables.
124 citations
TL;DR: In this paper, the lattice constants of the new compounds have been determined by powder X-ray diffraction, and the unit cells are tetragonal with a axes that are unchanged with variation of the intercalated amine.
116 citations
TL;DR: The gas phase reactions of Nb{sup +} with small alkanes and alkenes are reported in this article, which indicate a strong preference for C-H insertion, and reaction products indicate 1,3-hydrogen migration when β-hydrogens are not present.
Abstract: The gas-phase reactions of Nb{sup +} with small alkanes and alkenes are reported Nb{sup +} sequentially activates C-H bonds in ethene six times to produce NbC{sub 2n}H{sub 2n}{sup +} (n = 1-6) The C{sub 2}H{sub 2} ligands in this reaction couple via migratory insertion of the acetylene units Ethane sequentially reacts with Nb{sup +} five times Ligand coupling is proposed for these reactions as well Comparison of NbC{sub 4}H{sub 6}{sup +} produced from isobutane, n-butane, and ethane indicates the presence of at least two isomeric forms NbC{sub 4}H{sub 4}{sup +} ions produced from ethene, cyclobutane, and 1-butene produced similar CID spectra, supporting the presence of one structure Excited Nb{sup +} produced by direct laser desorption reacts with methane to produce NbCH{sub 2}{sup +} and NbCH{sub 3}{sup +}, but collisional cooling with argon quenches the reaction Primary reactions indicate a strong preference for C-H insertion, and reaction products indicate 1,3-hydrogen migration when {beta}-hydrogens are not present The reactions with alkanes are compared to those with Ta{sup +}, which reacts with CH{sub 4} four times to produce TaC{sub 4}H{sub 8}{sup +} Ta{sup +} and Nb{sup +}, which react similarly, are by far the most reactive metal ions toward C-H bond activation reportedmore » to date CID spectra of the products form the Nb{sup +} reactions indicate that the extensive dehydrogenation reactions occur via ligand coupling and, for larger alkanes (C{sub 5} and C{sub 6}), dehydrocyclization For example, Nb{sup +} undergoes a novel dehydrocyclization reaction with pentane to generate Nb(Cp){sup +} (Cp = cyclopentadienyl) Nb{sup +} reacts with cyclopentane to generate Nb(Cp){sub 2}{sup +} as a second product 34 refs, 3 figs, 2 tabs« less
109 citations
TL;DR: In this paper, the authors examined the electrical, magnetic and structural properties of Ta2NiS5/Ta2NiSe5 and showed that the properties are more consistent with the materials being small band gap semiconductors.
Abstract: The compounds Ta2NiS5 and Ta2NiSe5 have a novel layered structure: within the layers are rows of tantalum atoms separated by rows of nickel atoms. The lower dimensional structure of these compounds as well as the expected d1 non-bonding electron configuration of the tantalum atom leads to the expectation that classical charge density wave behavior would be observed in their properties. An examination of the electrical, magnetic and structural properties shows that this is not the case; rather, the properties are more consistent with the materials being small band gap semiconductors. Further, both compounds show structural phase transitions: in Ta2NiS5 a first-order transition occurs at 28 K and in Ta2NiSe5 a second-order transition occurs at 328 K. The latter transition is shown by electron microscopy to be martensitic-like.
100 citations
TL;DR: In this paper, a new anionic complex {[Nb6Cl12]Cl6}4− was presented, which contains the regular octahedral Nb6 cluster (dNb−Nb = 2.915 A).
Abstract: K4Nb6Cl18 last sich in kristalliner Form durch Erhitzen von Nb6Cl14 mit KCl oder einfacher aus KCl, Nb3Cl8 und Nb darstellen. Die Verbindung wird durch ihr chemisches, thermisches und optisches Verhalten charakterisiert. K4Nb6Cl18 kristallisiert monoklin in der Raumgruppe C—C 2/m (a0 = 9,97; b0 = 16,51; c0 = 9,47 A β = 115°). Die Struktur wurde durch optische Nachbildung der FOURIER. Transformierten und rechnerisch ausgefuhrte Verfeinerung bestimmt. Neuartig ist das Auftreten des anionischen Komplexes {[Nb6Cl12]Cl6}4−. Die darin enthaltene oktaedrische Nb6−=Gruppe ist regular (dNb−Nb = 2,915A K4Nb6Cl18) zeigt schwachen, von der Temperatur unabhangigen Paramagnetismus.
Crystalline K4Nb6Cl18 can be prepared by heating KCl/Nb6Cl14 or KCl/Nb3Cl8/Nb mixtures. The compound is characterized by its chemical, thermal and optical behaviour. It forms monoclinic crystals of space group C 2/m (C) (a0 = 9.97; b0 = 16.51; c0 = 9.47 A β = 115°). The structure found by optical synthesis of the FOURIER transform was refined by computational methods. This investigation showed a new anionic complex {[Nb6Cl12]Cl6}4− to be present, which contains the regular octahedral Nb6 cluster (dNb−Nb = 2.915 A). K1Nb6Cl18 posesses faint, temperature independent paramagnetism.
96 citations