Synthesis and characterization of dinuclear niobium(IV), niobium(III) and tantalum(III) chloride complexes with strongly basic phosphanes: PCy3 and P(Bu-t)3

Summary The reactions between niobium and tantalum pentachlorides and tri-t-butylphosphane and tricyclohexylphosphane under various reducing conditions (magnesium turnings, amalgamated magnesium or sodium naphthalenide) were investigated. The products are highly dependent on the experimental conditions. Niobium(IV) adducts: Nb₂Cl₈[P(Bu-t)₃]₂ and Nb₂Cl₈(PCy₃)₄ were obtained with magnesium turnings, while reduction to Ta₂Cl₆(PCy₃)₃ occurred under similar conditions with tantalum. Ligand exchanges from NbCl₄(THF)₂ also yielded niobium(IV) adducts Nb₂Cl₈(PR₃)₃. The formation of the first soluble diamagnetic niobium(IV) adducts appears to be favored by the strong basicity of PCy₃ and P(Bu-t)₃. However, these crowded niobium(IV) complexes are unstable both in the solid and in solution with respect to niobium(III). Derivatives in oxidation state 3: M₂Cl₆(PCy₃)₃ (M=Nb or Ta), Ta₂Cl₆[P(Bu-t)₃]₃ and Nb₂Cl₆[P(Bu-t)₃]₂ were formed more efficiently with amalgamated magnesium or with sodium naphthalenide. Activation of dinitrogen under mild conditions (normal pressure, room temperature) was observed during the reduction process with magnesium, for both tantalum and niobium; an unstable adduct, Nb₂Cl₆[P(Bu-t)₃]₃N₂, could be isolated. All products were characterized by elemental analysis, magnetic susceptibility measurements and i.r. spectroscopy; their molecular structure is discussed in terms of the¹H and³¹P n.m.r. data.     

Dissolution of niobium and tantalum matrix and their separation from trace elements by means of extraction with diantipyrylmethanes

Summary The separation of niobium and tantalum as matrices from other elements that appear as trace impurities was systematically examined by extraction with diantipyrylmethane and hexyl-diantipyrylmethane. The decomposition of the matrices in the HF/HNO₃ mixture was optimised by using the smallest possible quantities of nitric acid, because the presence of nitric acid hindered the efficiency of the separation. For the same reason the elimination of nitric acid from the sample solution by evaporation and also by decomposition with formic acid and urea was examined.Also taken into account in the examination was the behaviour of the trace elements to be determined during the decomposition of the samples and the removal of nitric acid. Arsenic, selenium and noble metals proved to be critical trace elements for which special measures are needed.The separation was undertaken under both static and dynamic conditions. For the elements Ag, Be, Cd, Co, Cr, Cu, Fe, Hf, Ir, K, La, Mo, Mn, Na, Ni, Se, Sc, Sn, Pa, V, W, Y, Zn and Zr, the separation yields are between 93% and 100% whereas in the case of the elements As, Au, Pd, Pt, Re and Sb a significant co-extraction takes place.

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Auflösung von Niob- und Tantalmatrix und ihre Abtrennung von Spurenelementen durch Extraktion mit Diantipyrylmethanen

Zusammenfassung Die Abtrennung von Niob und Tantal als Matrices von anderen als Spurenverunreinigungen vorkommenden Elementen durch Extraktion mit Diantipyrylmethan und Hexyl-Diantipyrylmethan aus HF-Medium wurde systematisch untersucht. Da die Anwesenheit von Salpetersäure die Effizienz dieses Trennverfahrens hemmt, wurde der Aufschluß der Matrices im HF/HNO₃-Gemisch optimiert und die Eliminierung von HNO₃ aus der Probelösung durch Eindampfen sowie durch Zersetzung mit Ameisensäure und Harnstoff überprüft.Mit einbezogen in diese Untersuchung wurde das Verhalten der zu bestimmenden Spurenelemente während des Aufschlusses und der Zersetzung von HNO₃. Arsen, Selen und die Edelmetalle haben sich dabei als kritische Spurenelemente erwiesen, für deren fehlerfreie Erfassung spezielle Maßnahmen erforderlich sind.Die Abtrennung wurde sowohl unter statischen als auch unter dynamischen Bedingungen vorgenommen.Bei den Elementen Ag, Be, Cd, Co, Cr, Cu, Fe, Hf, Ir, K, La, Mo, Mn, Na, Ni, Se, Sc, Sn, Pa, V, W, Y, Zn und Zr kann die Trennung mit einer Ausbeute zwischen 93 und 100% erreicht werden, während die Elemente As, Au, Pd, Pt, Re und Sb stark mitextrahiert werden.

     

Analysis of alloys of titanium,niobium and tantalum by ion exchange

A procedure for the analysis of alloys of titanium, niobium and tantalum is described. After dissolution the metals are separated by ion exchange in hydrochloric-hydrofluoric acid media. Finally the metals are determined spectrophotometrically,     

The determination of zirconium in its binary alloys with niobium and tantalum

A procedure is presented for the determination of zirconium in the presence of niobium or tantalum. The bulk of the niobium or tantalum is first removed by extracting with hexone from a 10M hyclrofluoric acid, 6M sulphuric acid solution of the sample. The zirconium is then. separated from any unextractcd earth, acid element by precipitation with ammonium hydroxide followed by the addition of hydrogen peroxide. Under these conditions, both the niobium and tantalum form soluble peroxy complexes whereas the zirconium is completely precipitated from solution. After the separation of the precipitate by filtration, it is re-dissolved in hydrochloric acid and the zirconium concentration is finally determined by titration with ethylenediaminetetraacetic acid.     

Furan derivatives of group IV elements (review)

Published data and the results of personal investigations on the methods of synthesis, chemical and physical properties, and biological activity of the furan derivatives of silicon, germanium, tin, lead, titanium, and zirconium are summarized.Latvian Institute of Organic Synthesis, Riga, Latvia, Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1690, December, 1995 Original article submitted June 3, 1995.     

Identification of phosphate anions in niobium and tantalum phosphates by means of infra-red spectra

Some niobium and tantalum phosphates have been prepared and their infra-red spectra have been recorded and compared with those of reference substances. It has been possible to identify P0₄^-3, P₂O₇^-4 and possibly P₃O10^-5 groups in different samples of niobium and tantalum phosphates.     

Nuclear magnetic resonance spectra of furan derivatives of IV B group elements (review)

Electronic and steric effects in furan derivatives were studied by the method of ¹H, ¹³C, ¹⁷O, and ²⁹Si NMR spectroscopy. The characteristic features of the influence of substituents on the screening and spin-spin interaction of ring nuclei in -substituted derivatives of furan in the presence of a second -substituent have been noted.Dedicated to Prof. A. R. Katritsky on his 65th birthday.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 879–890, July, 1993.     

Separation of niobium and tantalum by extraction chromatography with bis(2-ethylhexyl)phosphoric acid

A novel method is developed for the reversed-phase extractive chromatographic separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid. Niobium is extracted from 1-10M hydrochloric acid and can be stripped with 3M sulphuric acid containing 2% hydrogen peroxide. Tantalum is extracted from 0.1-2M hydrochloric acid and can be stripped with 0.1M hydrochloric acid containing 2M tartaric acid. It is possible to separate niobium and tantalum, in different ratios, from multicomponent mixtures.     

On the stabilization of niobium(V) solutions by zirconium(IV) and hafnium(IV)

Niobium cannot be separated from zirconium or hafnium when these elements occur together in solution with common anions such as chloride and sulphate. This is ascribed to the co-polymerization of niobium(V) and the hydrolysed ionic species of zirconium(IV) and hafnium(IV) to form colloidal particles. In hydrochloric acid the particles are positively charged, whereas in sulphate solution the Zr-and Hf-sulphate complexes confer a negative charge. The two cases are considered separately.     

Benzoyl hydrazone derivatives of niobium(V) and tantalum(V) ethoxides

Summary Niobium(V) and tantalum(V) pentaethoxides react with monofunctional benzoyl hydrazones (BHy) in refluxing benzene to give products of the type, M(OEt)_5–n(BHy)_n (where M=Nb or Ta and n=1, 2 or 3). The complexes have been characterised on the basis of elemental analysis, spectral (i.r. and n.m.r.) and molecular weight data.     

Novel poly(methimazolyl)borate complexes of niobium(V) and tantalum(V)

The reactions of [MCl4(eta-C5H5)](M = Nb, Ta) with Ph3Sn{HB(mt)3} (mt = methimazolyl) provide structurally characterised complexes of the new chlorobis(methimazolyl)borate ligand, [MCl3(eta-C5H5){kappa2-S,S'-HClB(mt)2}].     

Determination of niobium and tantalum in some ores and special alloys by inductively coupled plasma atomic emission spectrometry

A fast analytical method for the determination of niobium and tantalum in ores and special alloys by inductively coupled plasma atomic emission spectrometry has been developed. Optimum conditions for the determination of both metals in the plasma were worked out and possible interferences were studied before attempting the determination in the real samples. Ores are dissolved in a mixture of HCl, HF and H₃PO₄ acids while for the special alloy a HCl+H₂O₂ mixture is used. The resulting solutions are diluted to the mark with tartaric acid before their final direct nebulization into the plasma. Other elements present did not interfere in the determination of Nb or Ta at concentration levels similar to those found in the analyzed samples. The results obtained determining niobium and tantalum in pyrochlore and special alloys by the proposed procedure are in good agreement with the certified values.     

Tast polarographic determination of Thorium(IV) by means of substitution reduction of Bismuth(III)-ethylenediaminetetraacetate chelate

Summary Thorium(IV) facilitates the reduction of bismuth(III)-ethylenediaminetetraacetate chelate in weakly acidic medium and gives a new wave at a more positive potential, because the EDTA anion liberated by the reduction will be caught immediately by thorium(IV) ion. The height of the substitution reduction wave is proportional to the concentration of thorium(IV) between 0.1 and 0.6 mM. Properties of the wave and the electrode process were investigated.

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Tast-Polarographische Bestimmung von Thorium(IV) mit Hilfe der Substitutionsreduktion des Wismut(III)-Äthylendiamintetraacetat-Chelats

Zusammenfassung Thorium(IV) erleichtert die Reduktion des Wismut(III)-ÄDTE-Chelats in schwach sauerem Medium und gibt eine neue Welle bei positiverem Potential, da das durch die Reduktion freigesetzte ÄDTE-Anion vom Thorium(IV)-Ion sofort ergriffen wird. Die Höhe der Substitutionsreduktionswelle ist zwischen 0,1 und 0,6 mM der Thorium(IV)-Konzentration proportional. Eigenschaften der Welle und der Elektrodenvorgang wurden untersucht.

     

Analytical applications of infra-red spectroscopy : The behaviour of the oxinates of niobium,tantalum and associated elements

The behaviour of the oxinates of niobium, tantalum and associated metals in the infra-red region was studied and a method developed for the determination of niobium and tantalum. Vanadium caused no interference, but other heavy metals, such as molybdenum, manganese and cobalt, which interfered were removed by preliminary treatment when the method was applied to the determination of niobium and tantalum in steels.     

Separation of trace elements,In(III), Sn(IV), Sb(V) and Te(IV) by adsorption on activated carbon and graphite

Adsorption behaviour of trace elements, In(III), Sn(IV), Sb(V) and Te(IV) on activated carbon and graphite powder was studied. Adsorption characteristics of the ions enabled the separation of In(III)–Sn(IV), Sn(IV)–Sb(V) and Sb(V)–Te(IV) pairs. Applications to practical separation, milking of^113mIn from¹¹³Sn, removal of tin impurity from¹¹⁹Sb, and milking of¹¹⁹Sb from^119mTe, are presented.     

The separation of niobium from tantalum by extraction with tributyl phosphate and determination of niobium as the thiocyanate complex

A method is proposed for the rapid extraction and separation of microgram amounts of niobium(V). The niobium is extracted quantitatively by 100 % TBP from 7.7-9.4 M (initial) hydrochloric acid and determined spectrophotometrically as the thiocyanate in TBP-acetophenone solution. Beer's Law is obeyed at 430 mmu over the range 0.8-9.0 mug ml . The system is stable for 72 hr. Caesium, calcium, strontium, barium, aluminium, titanium(IV), zirconium(IV), cerium(TV), fluoride, thiocyanate and oxalate do not interfere (1 mg). Niobium(V) can be determined in a niobium(V)-tantalum(V) mixture. The method is accurate and reproducible to within +/-2%.     

Formation of aquatic Th(IV) colloids and stabilization by interaction with Cm(III)/Eu(III)

The present investigation is to ascertain under what conditions actinide ions undergo aggregation via oxo-bridging to form stable colloidal species. Eu and Th are taken for this purpose as trivalent and tetravalent actinide homologue ions, respectively. For verification of the effects of impurities in chemicals on the actinide colloid generation, pH is adjusted either by a conventional acid-base titration or by coulometry without addition of NaOH. The colloid generation is monitored by highly sensitive laser-induced breakdown detection in varying pH from 3 to 7, first in dilute Eu and Th solutions separately and then in a mixture of both, all in 0.5 M HCl/NaCl. The formation of stable colloids is observed particularly in a mixed solution of Eu and Th, suggesting that aggregation via mutual oxo-bridging of trivalent and tetravalent metal ions results in surface polarization, leading to stable hydrophilic particles of 20-30 nm in diameter. When Eu is replaced by Cm in the mixed solution in favor of the high fluorescence intensity of the latter, the chemical speciation is determined on colloid-borne Cm by time-resolved laser fluorescence spectroscopy. Two different colloid-borne Cm species, oxo-bridged with Th, are identified: a minor amount at 598.0 nm (denoted as Cm-Th(1)) and a major amount at 604.8 nm (Cm-Th(2)). The former is found as a transitional state, which converts to the latter with increasing pH and prevails at pH > 5.5. Both colloid-borne species (Cm-Th) are distinctively different from hydrolyzed Cm or its carbonate complexes with respect to their fluorescence peak positions and lifetimes. In conclusion, a mixed oxo-bridging of trivalent and tetravalent actinides elicits the generation of stable colloids, whereas individual ions in their pure state form colloids under oversaturation at near neutral pH only as a transitional state for precipitation.