Tantalum halides

Tantalum halides, 24 334—335 Tantalum hydride, 13 627 Tantalum junctions, 23 870-871 Tantalum metal, 24 314... 

Reactions of Tantalum(V) Chloride and Bromide with Pyridine. Table IV summarizes the reactions of niobium (V) and tantalum(V) halides with pyridine. In contrast to the niobium (V) halides, the reactions of these tantalum halides and pyridine were rapid and complete within a few minutes, and gave no evidence of reduction of the tantalum. 

Niobium and tantalum halides form adducts with various nitrogen donor ligands including aliphatic and aromatic amines nitriles, Schiffs bases and imidazoles (Table 5). The reactions of MXS with pyridine and related ligands such as bipy or phen depend critically on the reaction conditions. With py at low temperature MX5 (X = Cl, Br) yielded 1 1 adducts that are rapidly reduced to [MX4(py)2] on increasing the temperature, with formation of l-(4-pyridyl)pyridinium halide. Similarly, bipy and phen reduced the metal in MeCN to oxidation state +IV and formed monoadducts of type [MX bipy)] at room temperature, while at 0°C the same reactions yielded [NbCls(bipy)(MeCN)] and [TaX5(bipy)(MeCN)J (X = C1 or Br). NbBrs and Tals formed [MX5(bipy)2], which were formulated as the eight-coordinate [MX4(bipy)2]X.1 Reduction of the metal can however be prevented, even at room temperature,... 

Within the (M6Xi2) + (X = Cl, Br q = 2-4) cluster halides, the only series that cover all three oxidation states are the tantalum halide hydrates and the haloanions [(MsXi Xg] -. The isolation of [(Ta6Cli2)Cl2(PR3)4](PF6) (n = 1, 2) led to the first complete series of group VA cluster stabilized by an organic ligand. 

Organometallic Niobium ) and Tantalum ) Compounds. Reports this year have concerned two main areas of interest the preparation of alkyl-niobium and tantalum halides and their reactions with donor ligands, and insertion reactions into methyl-metal bonds. The first examples of monomethyl niobium and tantalum compounds have been prepared by the low-temperature methylation of the appropriate halides... 

We were quite optimistic in the beginning as the second reduction process corresponds to the formation of a black deposit which was potentially the first electrochemical route to make thick tantalum layers. After having washed off all ionic liquid from the sample we were already a bit sceptical as the deposit was quite brittle and did not look metallic. The SEM pictures and the EDX analysis supported our scepticism and the elemental analysis showed an elemental Ta/Cl ratio of about 1/2. Thus, overall we have deposited a low oxidation state tantalum choride. Despite the initial disappointment we were still eager to obtain the metal and found some old literature from Cotton [122], in which he described subvalent clusters of molybdenum, tungsten and tantalum halides. In the case of tantalum the well-defined Ta6Cli22+ complex was described with an average oxidation number of 2.33 and thus with a Ta/Cl molar ratio very close to 1/2. Such clusters are depicted in Figure 4.15. 

In this chapter we would like to present some plating protocols for the electrodeposition of aluminum, lithium, tantalum and zinc from different ionic liquids. These recipes have been elaborated in our laboratories and should allow the beginner to perform his first electrodeposition experiments. For aluminum we give four different recipes in order to show that the ionic liquid itself can strongly influence the deposition of metals. In the case of tantalum the deposition of the metallic phase is not straightforward as, in unstirred solutions, the more nonstoichiometric tantalum halides form the higher the current density for electrodeposition. Apart from the zinc deposition all experiments should be performed at least under dry air. 

CpCo(CO)2 under UV irradiation and from the polymerizations of metallolyl (57 and 58) and silyldiynes (66-70) catalyzed by tantalum halides [86-91]. The homopolycyclotrimerizations of other aromatic diynes (38-56) all proceeded very rapidly, giving polymeric products that were only partially or totally insoluble in common organic solvents due to the involved cross-linking reactions. The large free volumes and irregular molecular structures generated by the nonlinear carbazolyl, diphenylamine, metallolyl and silyl groups may have helped endow the homopolymers (hb-P57 to hb-P70) with the excellent solubility. 

Niobium and tantalum halides also fonn adducts with numerous N-donors. Their reactions with pyridine and related ligands (bipyridine, phenanthroline, 7-azaindole ) depend critically on the reaction conditions. Indeed, aromatic amines have a tendency to reduce the metal to oxidation state IV especially for niobium but the reduction can be prevented, even at rt, by an appropriate choice of the solvent (equations 2a-c). Imide adducts M(NR)Cl3L2 are obtained with primary or secondary amines. ... 

Formation of Heavy Transition Metal Group V Metal-Metal Bonds 9.2.8.2. In Niobium and Tantalum Halides Without Hexanuclear Cluster Units... 

In Niobium and Tantalum Halides Without Hexanuclear Cluster Units... 

Other studies of niobium or tantalum halides have included measurements of the vapour pressures of solid and liquid niobium and tantalum pentachloride, investi-... 

Table 1. Niobium and tantalum halide and oxyhalide series, based on discrete M6Lig units. 

Niobium and tantalum halides also react with isocyanides to give migration products [equation (12.51)]. Azide complexes react with CNR to afford coordination compounds with tetrazolyl [equation (12.52)]. Codimerization and cooligomerization of... 

COLOR AND VARIABLE VALENCE IN NIOBIUM AND TANTALUM HALIDES. 

B3 COLOR AND VARIABLE VALENCE IN NIOBIUM AND TANTALUM HALIDES, M.B. Robin and N.A. Kuebler... 

Niobium and tantalum halides yield salts of the 18 electron anions Nb(CO) and Ta(CO), but no neutral binary carbonyls have been isolated. 

The scientific community did not realize the importance of cluster compounds for nearly 40 years after their discovery. In the early 1900s tantalum halides of the general formula [Ta6Xi2] + were being prepared. In 1907 the chloride was incorrectly reported as TaCb. In 1910 the... 

A variety of polynuclear cations other than the Alj 3 Keggin ion have been used to pillar clays. Among them, we cite the zirconium tetramer [30,40,41,50,51], chromia polymers [52], bismuth [53], silicon [54], and niobium and tantalum halide clusters [55]. Of these, the most thoroughly studied have been zirconium polymers. 

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