Niobium pentabromide

Niobium Pentabromide. Niobium pentabromide is most conveniently prepared by reaction of bromine with niobium metal at ca 500°C. It is a fairly volatile yellow-red compound that is hygroscopic and readily hydrolyzes. It is soluble in water, alcohol, and ethyl bromide. 

Niobium Pentabromide, NbBrs.—This is the only bromine compound of niobium hitherto prepared. It is obtained by the action of bromine vapour on the coarsely powdered metal,2 or on a mixture of niobium pentoxide and carbon in the absence of air.2 In the latter case some of the oxybromide is also formed. Niobium pentabromide is a fine, purple-red powder, very similar to red phosphorus in appearance. The fused substance forms garnet-red prisms. On being strongly heated it becomes yellow, and volatilises. It melts at about 150° C., and distils undecomposed in an inert atmosphere at about 270° C. It can be distilled unchanged in an atmosphere of nitrogen or carbon dioxide. It is very hygroscopic, hydrolyses rapidly in damp air, and is decomposed by water with a hissing noise and considerable evolution of heat into niobie add and hydrobromic add. It is soluble in absolute alcohol and in dry ethyl bromide. 

NbBr5[g] NIOBIUM PENTABROMIDE (GAS) 1160 NI4B3 TETRANICKEL TRIBORIDE 1202... 

All solvents used in these reactions were purified by standard methods and purged with nitrogen immediately before use. The tributyltin hydride was either purchased from Aldrich Chemical Company and distilled prior to use (the checkers noted that they did not distill this material) or prepared from (Bu3Sn)20/polymethylhydrosiloxane. In the latter case we recommend that the tributyltin hydride be immediately redistilled (through a 2-cm x 30-cm Vigreux column) after the initial distillation from the reaction mixture. The niobium pentachloride (Aldrich or Cerac) and the niobium pentabromide (Cerac) were used as received. 

Caution. Tributyltin hydride is toxic and readily absorbed through the skin. Niobium pentachloride and niobium pentabromide are corrosive solids. 

A three-necked I-L flask is fitted with an overhead mechanical stirrer and a nitrogen inlet adapter and charged with dry 1,2-dimethoxyethane (600 mL) and tributyltin hydride (59.0 g, 0.203 mol). A 250-mL flask containing niobium pentabromide (50.0 g, 0.102 mol) is attached to the setup via a piece of Latex tubing (30 cm long, 1.8 cm in diameter) that is adapted with two male 24/40 joints on each end. The reaction mixture is cooled to — 78°C (Dry lce/2-propanol) and the solution is stirred vigorously while the NbBtj is added in portions over a 30-min period.t... 

Niobium Oxide Tribromide. Niobium oxide tribromide, NbOBr, is a yeUowbrown soHd which is readily hydrolyzed by moist air. It is prepared by reaction of bromine with a mixture of niobium pentoxide and carbon at 550°C. It decomposes in vacuum to the pentabromide and pentoxide at 320°C. 

Niobium Oxytribromide, NbOBr3, is prepared by the action of bromine on a mixture of niobium pentoxide and carbon. The method is that by which the pentabromide is produced, but in this case the proportion of carbon present is much smaller. The product is distilled in an atmosphere of bromine or nitrogen. It is a bright yellow, voluminous substance, which sublimes without melting in an atmosphere of bromine, but is converted completely into niobium pentoxide on being sublimed in an atmosphere of carbon dioxide. It fumes in damp... 

Definite compounds of niobium and iodine are unknown. The preparation of an iodide from the pentabromide has been reported2 but no details are supplied. A pyridine addition compound of the pentiodide, NbIB.(C5H5N.HI)6, has been described,2 but its existence lacks confirmation.4... 

Group-5 elements are most stable in their maximum oxidation state +5 and therefore form pentahalides, see Figure 7. Most volatile are the pentafluorides, followed by the pentachlorides and the pentabromides. Besides the pure halides, also the oxyhalides (MOX3) are stable in the gas phase. They should be less volatile compared to the pure halides. This was confirmed experimentally for niobium, see Figure 8. 

Protactinium pentachloride (42) and pentabromide (43) form both 1 1 and 1 2 complexes with phosphine oxides, the former being analogous to those formed by niobium, tantalum, and uranium pentahalides (26, 42, 43). Unlike niobium and tantalum pentachloride (42, 64) however, they do not react with excess triphenylphosphine oxide (TPPO) to form... 

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. 

Roscoe discovered tungsten pentachloride and pentabromide, uranium pentachloride,2 and niobium trichloride (which he found gave NbOClg and CO when heated in COg). He determined the vapour densities of PbClg and TlCl, showed that Delafontaine s supposed new rare-earth metal philippium is a mixture of yttrium and terbium, and redetermined the atomic weight of carbon (C = 12 002). Roscoe published several papers and a book on spectrum analysis. 

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