Niobium complexes applications

Niobium, tris(diethyldilhiocarbamato)oxy-stereochemistry, 1,82 structure, 1, 83 Niobium, tris(oxa ato)oxy-stereochcmistry, 1, 82 Niobium, tris(phcnylcncdirhio)-structure, 1, 63 Niobium alanate, 3, 685 Niobium complexes alkyl alkoxy reactions, 2, 358 amides, 2,164 properties, 2, 168 synthesis, 2, 165 applications, 6,1014 carbamicacid, 2, 450 clusters, 3, 672,673,675 hexamethylbenzene ligands, 3, 669 cyanides synthesis, 2, 9 p-dinitrogen, 3, 418 fluoro... 

Doye s group [81] showed that a dinuclear titanium-sulfonamidate complex (Scheme 21), with a tetrahedral sulfur in the ligand backbone, can be used for intermo-lecular hydroaminoalkylation as well. This system gives mixtures of branched and linear products, although to date there has been no mechanistic rationale provided for the reduced regioselectivity of group 4 metal complexes in this transformation. There has been one report by Zi s group [44] that describes axially chiral bis(sulfonamidate) tantalum and niobium complexes for application as precatalysts for hydroamination and hydroaminoalkylation. Unfortunately, these complexes did not show any reactivity for either of these reactions. 

The route shown in Fig. 9.12 is one which has been operated commercially in the U.K. on a fairly small scale, quite successfully. As in the case of niobium, it is convenient to use the crude ferro alloy as feed to the chlorination stage. The chloride purification stages lead to pure vanadium trichloride, which is reduced with magnesium in a manner similar to that employed for titanium, zirconium or hafnium. Some of the complexities, applicable in the latter processes owing to the volatile nature of the chlorides, are absent with vanadium. The vanadium metal sponge has some properties in common with the other metal sponges. 

Since niobates and tantalates belong to the octahedral ferroelectric family, fluorine-oxygen substitution has a particular importance in managing ferroelectric properties. Thus, the variation in the Curie temperature of such compounds with the fluorine-oxygen substitution rate depends strongly on the crystalline network, the ferroelectric type and the mutual orientation of the spontaneous polarization vector, metal displacement direction and covalent bond orientation [47]. Hence, complex tantalum and niobium fluoride compounds seem to have potential also as new materials for modem electronic and optical applications. 

Since the fluorination enables to separate components of complex oxide compounds containing tantalum and niobium, it seems that it is applicable for... 

Although the elements tantalum and niobium were discovered more than 200 years ago in the form of oxides, the true beginning of the chemistry of tantalum and niobium was the discovery and investigation of complex fluorotantalates and fluoroniobates of alkali metals. Application of complex fluoride compounds enabled the separation of tantalum and niobium and in fact initiated the development of the industrial production of the metals and their compounds. 

Applications of heteroligand complexes in the analytical chemistry of niobium and tantalum. S. V. Elinson, Russ. Chem. Rev. (Engl. Transl.), 1975,44, 707-717 (131). 

The chapters for niobium and tantalum in COMC (1982) and COMC (1995) provide an in-depth discussion concerning complexes of these metals as well as their applications to catalysis.172 173 Alkylcyclopentadienyl complexes of niobium and tantalum have also been reviewed.1 Similarly to vanadium (Section 10.09.4.1.2), the... 

Niobium oxide (niobia) is an active catalyst, and can be used as a support for metal nanoparticles or oxides, and it can serve as a promoter in some reactions ([43 5] and references therein). Catalytic applications of niobia include the Fischer-Tropsch synthesis, oxidative dehydrogenation of alkanes, and oxidative coupling of methane. Studies on high-surface-area niobium oxides are complicated by a high degree of complexity because several stable structures (NbO, NbO and Nb O ) exist and the resulting surfaces of high-surface-area niobium oxides are not simple truncations of bulk niobia structures. This is even more so for supported metal oxides when two-dimensional thin films of niobium oxide partially cover a support oxide (Al Oj, SiOj, ZrOj, TiOj, [43]). Nb Oj was also used as a support for V, Cr, Re, Mo, and W oxide overlayers [45, 46]. 

Among the pentavalent elements, the most important are niobium and tantalum. Niobium is an excellent material for surface treatment of steel materials for chemical industry due to its high hardness and corrosion-resistance in wet acidic conditions. Nowadays, niobium is also used for the preparation of superconductor tapes and it is used in other branches of industry, for instance in nuclear technology and metallurgy. Tantalum is also of similar importance. For these applications, it is necessary to prepare high purity metal. Molten salt electrolysis, as an alternative process to classical thermal reduction, provides niobium and tantalum with required quality. In order to optimize these processes, it is necessary to know details of both complex formation and redox chemistry of the species present in the melts. 

The crucial problem in niobium deposition in molten salts is the presence of oxygen in the electrolyte, because it is extremely difficult to prepare a melt free of 0 ions, especially in the case of industrial applications. It was formerly assumed that the presence of ions might decrease the quality of Nb coatings or prevent the formation of Nb coatings completely. Therefore a great part of the research efforts was concentrated on the influence of ions on the reduction mechanism of Nb and the formation of niobium oxofluoro-complexes in the melt. 

In addition to their applications in organic synthesis, all of the niobium halide complexes described here serve as convenient precursors to a variety of known coordination complexes of niobium(III) and (IV) as well as organo-metallic compounds. ... 

Niobium pentoxide, Nb20s, acts as a smoke retarder for poly(vinyl chloride) but is less effective than V2O5. Tantalum pentoxide is even more limited and is unlikely to find application. Phosphinate complexes of tantalum have been used as fillers for special purpose high temperature laminates. They are polymeric species of the stoichiometry [Ta(0PPh20)2(0H)3] . ... 

---