- Process for the preparation of high-purity zirconium, hafnium, tantalum and niobium alkoxides
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A novel process for the preparation of high-purity zirconium, hafnium, tantalum and niobium alkoxides (alcoholates), novel tantalum and niobium compounds and a process for their preparation are provided. The process comprises the steps of mixing crude metal alkoxides M(OR)x having a halogen impurity of at least 0.05 wt. %, with an alcohol ROH, in which R is a C1-C12-alkyl radical, and subsequently or simultaneously metering in an excess of ammonia, based on the amount of mononuclear or polynuclear halogen-containing metal alkoxides.
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- Synthesis and structural study of polynuclear lithium oxoethoxo tantalates
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LiTa9O13(OEt)20·2EtOH (I) is a side product of the electrochemical synthesis of Ta(OEt)5 carried out using LiCl as a supporting electrolyte. This product crystallizes in a minor yield upon the storage of crude liquid Ta(OEt)5. Treatment of I with a hot ethanol solution of LiOEt yields Li8Ta8O 14(OEt)20·12EtOH (II). The structures of I and II have been determined using X-ray crystallography. Molecule I, LiTa 9H(μ3-O)4(μ-O)9(μ-OEt) 6(OEt)15(EtOH), is located on a threefold axis that passes through the lithium atom, which coordinates one disordered solvation ethanol molecule and three μ3-oxo groups belonging to the [Ta 6O6(OR)15] ring fragment made of six octahedra. The next layer is formed by the [Ta3O7(OR)6] fragment made of three octahedra linked to the previous fragment through six μ-oxo ligands. In molecule II, Li8Ta8H 8(μ4-O)2(μ3-O) 8(μ-O)4(μ3-OEt)2(μ-OEt) 10(OEt)16·4EtOH, one can distinguish two groups of four [TaO6] octahedra that form [Ta4] tetrahedra sharing two vertices represented by μ4-oxo groups. Four Li atoms are located between the [Ta4] tetrahedra thus forming a interlayer comprising two distorted [LiO4] tetrahedra and two distorted [LiO5] tetragonal pyramids. The other four tetrahedrally coordinated Li atoms are located on the periphery of the molecule and are linked through [O(OR)] edges with Ta atoms. Each Ta atom coordinates three terminal OR groups and one μ-OR group. Four solvation ethanol molecules are hydrogen-bonded with the terminal OR groups at Ta atoms.
- Starikova,Turova,Cheboukov,Yanovsky
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p. 1156 - 1162
(2008/10/08)
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- Heterometal Alkoxides of Tantalum: Lithium, Magnesium, and Barium Alkoxotantalates
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The formation of bimetal alkoxides of tantalum with Li, Mg, and Ba was studied by constructing solubility diagrams for the M(OR)n-Ta(OR)5-ROH (M = Li, Mg, Ba; R = Me, Et, i-Pr, n-Bu) systems at 200C. LiTa(OR)6 (R = Mc, Et, n-Bu), BaTa2(OPr-i)12 . 2i-PrOH, and MgTa2(OR)12 . 2ROH (R=Et, i-Pr) complexes were found to exist in the crystalline state. Their crystallization branches are located in the Ta(OR)5-rich regions relative to compositions of the complexes. Crystalline alkoxotantalates do not form in the systems involving Mg(OMe)2, Ba(OEt)2, and Mg(OBu-n)2. However, the location of the solubility curves of MII(OR)2 suggests the formation of MII : Ta = 1 : 2 complexes in solution, and this was confirmed by electrical conductivity and viscosity measurements on isomolar series of solutions. No complexes form between barium and tantalum butoxides. Fragments of MIITa2(OR)12 (R=Me, Et, i-Pr) and [LiTa(OR)6]2 molecules were detected massspectrometrically (the latter result from the oligomerization of polymeric chains existing in the solid phase). Long-term storage in alcoholic solutions causes the decomposition of the alkoxotantalates yielding crystalline LiTa9O13(OEt)20 · 2ROH, [LiTaO(OEt)4(EtOH)]2, [BaTaO(OMe)5(MeOH)2.5]4, [BaTaO(OEt)5(EtOH)1.5]4, and [MgTaO(OBu-n)5(n-BuOH)]4 oxoalkoxotantalates. The solvate LiOPr-i · 2i-PrOH and its behavior in i-PrOH were described for the first time.
- Tchebukov,Turova,Korolev,Belokon'
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p. 1498 - 1508
(2008/10/08)
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