- Preparation and crystal structure of new one-dimensional Ta selenide: [Ta(Se2)2]2TaBr6
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Compound [Ta(Se2)2]2TaBr6 was prepared from elements by high temperature (450°C) stoichiometric reaction in high yield. The structure has been determined by single crystal X-ray diffraction. It contains infinite positively charged chains Ta(Se2)2. . . separated by octahedral TaBr6- anions. The slightly alternating Ta-Ta distances within the chains [3.182(2)-3.234(2) A] show a considerable degree of metal-metal interaction along the chain.
- Sokolov, Maxim,Imoto, Hideo,Saito, Taro,Fedorov, Vladimir
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- Synthesis and structure of Ta4S9Br8. An emergent family of early transition metal chalcogenide clusters
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Single crystals of Ta4S9Br8 are obtained by heating Ta, S, and Br2 at 400°C in a 4.0:9.0:4.0 molar ratio in a 44% yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(μ4-S)(μ-S2) 4Br8]. The tantalum atoms form a square with long Ta...Ta distances (3.30 A), with four S2 ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding. IR and Raman spectral studies with the use of 34S allow to identify characteristic vibrations S-S (537 cm -1) and Ta4-μ4-S (407 cm-1). The compound is soluble in CH3CN, giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT calculations. ESI-MS spectra of the solutions show formation of {[Ta 4S9Br8]Br}- associates.
- Sokolov, Maxim N.,Gushchin, Artem L.,Abramov, Pavel A.,Virovets, Alexandr V.,Peresypkina, Eugenia V.,Kozlova, Svetlana G.,Kolesov, Boris A.,Vicent, Cristian,Fedin, Vladimir P.
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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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- Chemistry of polynuclear metal halides. I. Preparation of the polynuclear tantalum halides Ta6X14
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The anhydrous halides (Ta6X12)X2 (X = Br, I) have been produced in good yields by the reduction of the tantalum(V) halides with aluminum foil in a temperature gradient according to the reaction 18TaX5(g,l) + 16Al(s) = 3(Ta6X12)X2(s) + 16AlX3(g,l). Final products having atom ratios X/Ta smaller than the calculated 2.33 were shown to contain some tantalum metal. A lower tantalum chloride mixture was prepared by the same procedure, but evidence indicated the principal phase present was TaCl2.5 (Ta6Cl15). However, good yields of the ion Ta6Cl122+ could be obtained in solution from the anhydrous solids. Reflectance spectra of the anhydrous solids and absorption spectra of aqueous solutions were determined. The spectra were found to exhibit bands very characteristic of the Ta6X122+ structure.
- Kuhn, Phyllis J.,McCarley, Robert E.
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- The preparation of tantalum(IV) bromide, tantalum(IV) iodide, and pyridine adducts of the tantalum(IV) halides
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The necessary conditions for preparation of TaBr4 and TaI4 by reduction of the pentahalides with tantalum or aluminum metal in a sealed tube under a controlled temperature gradient have been demonstrated. An unusual, but more fruitful synthesis of TaI4 was devised from the reduction of TaI5 with pyridine. X-Ray powder patterns of diamagnetic, isomorphous TaCl4 and TaBr4 were indexed on an orthorhombic unit cell of dimensions a = 8.10, b = 8.92, c = 6.80 ?. and a = 8.58, b = 9.30, c = 7.21 ?., respectively. The compounds TaCl4(C5H5N)2 and TaBr4(C5H5N)2 were prepared by the reaction of pyridine with the respective tetrahalides at room temperature. Unusually low magnetic moments of 0.69 and 0.43 B.M. were found for the chloride- and bromide-pyridine adducts, respectively.
- McCarley,Boatman
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- Thermochemistry of lower bromides of tantalum
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The standard enthalpy of formation of tantalum(IV) bromide has been determined by solution calorimetry: ΔH0f(TaBr4(c) 298 K) = -125.6+-0.5 kcal mol-1.Experimental estimates of the enthalpies of formation of tantalum(III) b
- Westland, Alan D.
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p. 938 - 941
(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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- The equilibrium phase diagrams for the tantalum-tantalum bromide and tantalum-tantalum iodide systems
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The tantalum-tantalum bromide and the essential features of the tantalum-tantalum iodide system have been elucidated. In the bromide system four phases of composition lower than TaBr5 were established, viz., TaBr4, TaBr2.5, TaBr2.5, and TaBr2.33. By comparison the iodide system is very simple as evidenced by only the two lower phases TaI4 and TaI2.33. In the bromide system a eutectic occurs at 267° and the composition TaBr4.87. The TaBr4 melts incongruently at 392° to form liquid of composition near TaBr4.85 and the next lower solid TaBr2.83. Equilibrations of TaBr4 at a series of temperatures above 400° established that TaBr2.83 melts incongruently within the interval 447-453° to form bromine-rich liquid and the phase TaBr2.5. Similarly it was determined that TaBr2.5 melts incongruently to form TaBr2.33 in the interval 671-680°. Exact location of the melting temperatures for the bromides with Br/Ta 2.33 was the lowest phase in the system was established by equilibrations of the higher halides with tantalum at temperatures up to 750°; a melting point for TaBr2.33 was not observed. In the iodide system the melting point of TaI5 occurred at 382°, with a eutectic at 365° and the composition TaI4.87. Decomposition of TaI4 into iodine-rich liquid and TaI2.33 occurred in the interval 395-402° at a very low rate. Equilibrations of TaI2.33 and Ta up to 815° provided no evidence for any new phases. Both TaBr2.33 and TaI2.33 provide aqueous solutions of the ions Ta6Br122+ and Ta6I122+. Hence these compounds are formulated correctly as (Ta6Br12)Br2 and (Ta6I12)I2. The chemical properties and stoichiometry of the phases TaBr2.5 and TaBr2.83 suggest that they should be formulated as (Ta6Br12)Br3 and (Ta6Br12)Br5, respectively.
- McCarley, Robert E.,Boatman, James C.
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p. 1486 - 1491
(2008/10/08)
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