Tantalum compounds synthesis

We then studied group 5 metals, especially tantalum-for which the laboratory already had great experience. Because of the studied reaction, alkyl or hydride-type compounds such as those developed in the laboratory could not be employed. Consequently, we became interested in alkoxo-type derivatives, either synthesized by reaction of the grafted complex with an alcohol or obtained by direct synthesis starting from an alkoxy-tantalum compound grafted on silica. In all cases, resulting complexes have been characterized by surface organometallic chemistry techniques, especially EXAFS and solid-state NMR (ID and 2D with C-labeled compounds). Indeed various compounds bonded by one, two or three surface bonds have been prepared and characterized. 

Tantalum Nitrides. Tantalum nitride [12033-62-4] TaN, is produced by direct synthesis of the elements at 1100°C. Very pure TaN has been produced by spontaneous reaction of lithium amide, L1NH2, and TaCl ( )- The compound is often added to cermets in 3—18 wt %. Ta N [12033-94-2] is used as a red pigment in plastics and paints (78). 

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... 

The synthesis of tantalum and niobium fluoride compounds is, above all, related to the fluorination of metals or oxides. Table 3 presents a thermodynamic analysis of fluorination processes at ambient temperature as performed by Rakov [51, 52]. It is obvious that the fluorination of both metals and oxides of niobium and tantalum can take place even at low temperatures, whereas fluorination using ammonium fluoride and ammonium hydrofluoride can be performed only at higher temperatures. 

Synthesis of the compounds from such HF solutions is performed by adding soluble fluoride compounds to the tantalum or niobium solution or by recrystallization of prepared fluoride compounds from water or HF solutions of different concentrations. In the first case, the composition of the compounds obtained depends on the ratio between Ta/Nb and the added metal and on the initial concentration of the HF used, whereas in the second case, it depends only on the HF concentration. 

Potassium-containing tantalum and niobium fluoride compounds can be precipitated from HF solutions as described previously (see Fig. 3 and 4). Ritchie and Mitra [59] described the synthesis of K.2TaF7 in an HF solution, based on the following interaction (5), using TaCl5 as a precursor ... 

Attempts to obtain fluoride compounds of niobium and tantalum with alkali earth and some transitional metals were made as early as one hundred years ago, but synthesis and identification methods were described only at later times. 

The results available on the synthesis of niobium and tantalum fluoride compounds from aqueous solutions are in good correlation with the concept of... 

Another anhydrous solvent that is frequently used for the synthesis of tantalum and niobium fluoride compounds is bromine trifluoride, BrF3. At ambient temperature, bromine trifluoride is light yellow liquid characterized by a boiling point of 126°C, a melting point of 9°C and a density of 2.84 g/cm3 at melting temperature. 

The most universal method for the synthesis of tantalum and niobium fluoride compounds is based on direct interaction between their pentafluorides, TaF5 or NbFs, and fluorides of other metals. Some physical-chemical properties of these compounds are presented in Table 8 [71, 72]. 

Niobium dioxyfluoride, Nb02F, and tantalum dioxyfluoride, Ta02F, can be successfully used as precursors for the synthesis of many oxyfluoride compounds of niobium and tantalum. Systematic investigations performed on MeC>2F - M2CO3 systems, in which Me = Nb or Ta and M = alkali metal, provided necessary information on optimal synthesis procedures and imparted some conformity on the mechanism of the chemical interaction between the components. 

Hydrofluoride synthesis is based on the simultaneous fluorination by ammonium hydrofluoride of niobium or tantalum oxides with other metals compounds (oxides, halides, carbonates etc.) [105]. Table 13 presents some properties of ammonium hydrofluoride, NH4HF2 [51, 71]. Ammonium hydrofluoride is similar to anhydrous HF in its reactivity, but possesses some indisputable advantages. The cost of ammonium hydrofluoride is relatively low, it can be dried and handled easily, recycled from gaseous components, and its processing requires no special equipment. 

Since hydrofluoride synthesis is based on thermal treatment at relatively high temperatures, the possibility of obtaining certain fluorotantalates can be predicted according to thermal stability of the compounds. In the case of compounds whose crystal structure is made up of an octahedral complex of ions, the most important parameter is the anion-cation ratio. Therefore, it is very important to take in to account the ionic radius of the second cation in relation to the ionic radius of tantalum. Large cations, are not included in the... 

For a long period of time, molten salts containing niobium and tantalum were widely used for the production by electrolysis of metals and alloys. This situation initiated intensive investigations into the electrochemical processes that take place in molten fluorides containing dissolved tantalum and niobium in the form of complex fluoride compounds. Well-developed sodium reduction processes currently used are also based on molten salt media. In addition, molten salts are a suitable reagent media for the synthesis of various compounds, in the form of both single crystals and powdered material. The mechanisms of the chemical interactions and the compositions of the compounds depend on the structure of the melt. 

The first alkali metal-niobium-arsenic compounds were synthesized by accident while attempting the synthesis of alkali-metal main-group arsenides at relatively high temperature. It turns out that niobium and tantalum containers react readily... 

However, over the past decade, advances in, and in particular the availability of sophisticated instrumentation, and in the understanding of the instrumental techniques and the hosts and guests to which they are applied, mean that this need no longer be the case. A recent example in which a gamut of carefully chosen techniques, including such basic but essential measurements as elemental analyses, has led to the same precise characterization of surface species as has been the mainstay of molecular compounds is the study of the synthesis, characterization and reactivity of tantalum hydrides on silica, and their involvement in the dissociation of dinitrogen [203]. 

Ni and Co or of oxophilic metals, for example. Re, is still poorly studied the surface-mediated synthesis of bimetallic carbonyl clusters is limited to a few examples the surface-mediated synthesis of metal compounds without carbonyl ligands has just begun with the silica-mediated synthesis of [RhH2(PMe3)4] by treatment of bis (allyl) rhodium with PMe3 followed by H2 [121] the silica-mediated synthesis of tantalum clusters has been investigated recently but the products were not extracted from the surface-for example, treatment of silica physisorbed Ta(CH2Ph)5 in H2 at 523 K for 20 h led to tri-tantalum clusters, as shown by EXAFS spectroscopy [122]. 

Compounds containing niobium or tantalum in negative formal oxidation states -I and -III are mainly metal carbonyl anions. Although these are organometallic derivatives, the report of efficient procedures for the synthesis of [M(CO)6] since the review of Labinger8 merits mention, as it can be anticipated that these highly reduced and reactive species will be important precursors of a large variety of new coordination compounds and metal clusters. 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

Although the number of tetrafluorides reported is as large as the number of di- and trifluorides (see Table III), this group of compounds is the least well characterized structurally of the transition metal fluorides. The synthesis of most of the expected tetrafluorides has been reported, with examples from titanium to manganese in the first, from zirconium to palladium (except for technetium) in the second, and from hafnium to platinum (except for tantalum) in the third series. Many of them have been little studied and, in general, they have not proved amenable to crystallographic structural analysis. 

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