Niobium tetrachlorides

The A-trimethylsilylimines 68 (R = t-Bu, Ph, 2-MeCgH4 or 2-BrC6H4), which are prepared by the reaction of non-enolizable aldehydes with lithium bis(trimethylsilyl)amide, followed by trimethylsilyl chloride, undergo pinacolic coupling induced by NbCLt 2THF to yield the vicinal diamines 69 as mixtures of dl- and meso-isomers, in which the former predominate. Another method for the preparation of 1,2-diamines is by the combined action of the niobium tetrachloride/tetrahydrofuran complex and tributyltin hydride on cyanides RCN (R = /-Hu. Ph, cyclopentyl or pcnt-4-en-l-yl) (equation 32)82. 

Niobium Tetrachloride is reported to have been obtained in solution by the electrolytic reduction of a solution of sodium niobate in hydrochloric acid.7... 

In an inert-atmosphere dry-box, 2.36 g (0.01 mole) of niobium tetrachloride is suspended in 25 ml of acetonitrile in a 100-ml round-bottomed flask equipped with a magnetic stirring bar. Niobium(IV) chloride is conveniently prepared by reduction of niobium(V) chloride with aluminum metal. " This mixture is stirred for ca. 1 hr and then 5.84 g (0.06 mole) of potassium thiocyanate dissolved in 25 ml of acetonitrile is added. Stirring is continued for 4 hr to allow for complete reaction. The red solution is filtered through a medium-porosity sintered-glass frit, separating the insoluble potassium chloride from the soluble K2[Nb(NCS)e]. The KCl precipitate is washed with three 5-ml portions pf... 

The method described above has been found suitable for the synthesis of Nb(NCSe)4(CioH8N2)2, Nb(NCS)4(dmbipy)2, and Nb(NCSe)4(dmbipy)2, where dmbipy is4,4 -dimethyl-2,2 -bipyridine. These niobium (IV) compounds can also be prepared from the hexakis(isothiocyanate)niobate(V) complex. The sensitivity of the materials to air and moisture makes the method somewhat more time-consuming, but the use of niobium tetrachloride as a starting material is avoided. The tantalum(V) complexes, Ta(NCS)6(CioH8N2)... 

A 125-mL Erlenmeyer flask equipped with a magnetic stirring bar is charged with 1.6 g aluminum powder and 50 mL dry acetonitrile. To this suspension is added with stirring 4.8 g (18mmole) niobium tetrachloride. After stirring under... 

Na2F2[g] DISODIUM DIFLUORIDE (GAS) 1124 NbCI4 NIOBIUM TETRACHLORIDE 1167... 

Any niobium tetrachloride which enters this stage is successfully reduced to the trichloride along with the pentachloride, i.e. 

Mixtures of the MCI alkali halides with NbCl4 niobium tetrachloride and NbCl3... 

The action of carbon tetrachloride or a mixture of chlorine with a hydrocarbon or carbon monoxide on the oxide.—H. N. Warren 9 obtained aluminium chloride by heating the oxide to redness with a mixture of petroleum vapour and hydrogen chloride or chlorine, naphthalene chloride or carbon tetrachloride was also used. The bromide was prepared in a similar manner. E. Demarpay used the vapour of carbon tetrachloride, the chlorides of chromium, titanium, niobium, tantalum, zirconium, cobalt, nickel, tungsten, and molybdenum H. Quantin, a mixture of carbon monoxide and chlorine and W. Heap and E. Newbery, carbonyl chloride. 

The pentavalent halides and oxyhalides, as in the case of other niobium compounds, are the most stable. It is remarkable that the pentavalency is maintained with increase in the atomic weight of the halogen. All the halogen compounds are characterised by their ready tendency to undergo hydrolysis on the addition of water or even in damp air with precipitation of niobie acid and formation of the hydrogen halide. Their preparation can, therefore, be effected only in the dry way (a) synthetically, or (b) by the action of chlorine, carbon tetrachloride, or sulphur monochloride on the oxide or sulphide. They do not possess saline properties, and cannot be prepared by the action of the halogen acids on the oxide. 

Niobium Trichloride, NbCl3, is prepared by leading the vapour of niobium pentachloride through a heated tube.4 It is also formed in small quantity by the action of carbon tetrachloride vapour on niobium pentoxide contained in a hard-glass tube, and has probably been prepared in solution by the electrolytic reduction of the pentachloride.4 It forms a black, crystalline crust with an almost metallic lustre, which closely resembles the appearance of a film of sublimed iodine. It is not decomposed by water or ammonia, but is readily oxidised by dilute nitric add to niobium pentoxide. On being heated to a red heat in an atmosphere of carbon dioxide, a sublimate of niobium oxytrichloride, NbOCl3, is produced, the carbon dioxide undergoing reduction to the monoxide. 

Niobium oxytrichloride is prepared by the action of chlorine on a mixture of niobium pentoxide and carbon, or on the lower oxide, NbO 5 or by the action of the vapours of carbon tetrachloride on the pentoxide. Some niobium pentachloride is produced in the same reaction, and this is removed either by distilling it away at the lowest temperature possible in an atmosphere of carbon dioxide, or by subliming the product in a current of chlorine over the ignited oxide.7 The oxychloride has also been prepared by passing the vapours of niobium pentachloride over niobium pentoxide at a red heat.8... 

The form of molybdenum(IV) chloride obtained by the above method has been labeled the low-temperature a-isomer because of its structural similarity with the other tetrachlorides of tungsten, niobium, and tantalum and to distinguish it from the higher-temperature /8-isomer prepared from molybdenum(III) chloride and molybdenum(V) chloride. The /3-isomer may be obtained by heating the low-temperature form at 250°C. in a sealed tube with molybdenum(V) chloride for 24 hours. The excess molybdenum (V) chloride is sublimed away at 125°C. Because of its structural difference, the /S-isomer possesses a considerably higher paramagnetism and thermal stability than the a-isomer. 

Oxidizer, Poison, Corrosive SAFETY PROFILE Poisonous and corrosive. Very reactive, a powerful oxidizer. Explosive or violent reaction with organic materials, water, acetone, ammonium halides, antimony, antimony trichloride oxide, arsenic, benzene, boron, bromine, carbon, carbon monoxide, carbon tetrachloride, carbon tetraiodide, chloromethane, cobalt, ether, halogens, iodine, powdered molybdenum, niobium, 2-pentanone, phosphoms, potassium hexachloroplatinate, pyridine, silicon, silicone grease, sulfur, tantalum, tin dichloride, titanium, toluene, vanadium, uranium, uranium hexafluoride. 

Since niobium pentachloride and tetrachloride decompose readily in the presence of oxygen or moisture, all solvents and vessels used in the reactions must be dried by accepted methods. The niobium chlorides should also be free of any oxy species. The potassium thiocyanate and 2,2 -bipyridine should be purified by recrystallization from water and ether, respectively, and then dried at a pressure of ca. 10" torr for 72 hrs. 

This procedure has been used to prepare many other chlorides, e.g., tungsten hexachloride, vanadium tetrachloride, and the pentachlorides of niobium and tantalum. However, it is normally much easier to prepare chlorides than fluorides. This method will therefore find application only where this generalization is not applicable. In particular, it will find application where the chloride is thermally unstable under normal chlorination conditions and must be prepared at or below room temperature. This method has been used to advantage for the preparation of ReCle and the new compound osmium pentachloride. ... 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

Tungsten(VI) oxide tetrachloride is a common impurity in tungsten(VI) chloride. By anaiogy with niobium(V) oxide trichloride (Section 9.2.2), phosgene might have been expected to convert WOCi to WClj, according to ... 

The bathophenanthroline method was used for determining iron in blood plasma [157], in plant materials [158], in waters [159], in niobium, tantalum, molybdenum, and tungsten [42,160], in molybdenum compounds [161], in cobalt [162], in cadmium and cadmium telluride [5], platinum [163], synthetic rubies and sapphires [164], silicon tetrachloride [165], and in boiler water [166]. 

The method involving the Mo-V-P acid has been used in determinations of phosphorus in biological tissues [127], plant material [128], fruits [129], fish products [130], foodstuffs [131], phosphate minerals [132], cast iron and steel [133,134], niobium, zirconium and its alloys, titanium and tungsten, aluminium, copper, and white metal [135], nickel alloys [134,135], metallurgy products [136], molybdenum concentrates [137], silicon tetrachloride [7], cement [138], and lubricants[139]. The flow injection technique has been applied for determining phosphate in minerals [140] and in plant materials [141]. 

Cl4Nb02CgH,g, Niobium, tetrachlorobis-(tetrahydrofuran)-, 29 120 CI4OW, Tungsten tetrachloride oxide,... 

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