Niobium pentachloride Reduction

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. 

Preferential reduction of niobium pentachloride to the trichloride by the excess of hydrogen still present is used in the next stage, to separate from tantalum pentachloride, which remains volatile, i.e. 

Low-valent niobium, formed by the mixing of niobium pentachloride and sodium aluminium hydride, reductively couples ketones to give olefins in high... 

Several methods are described for the production of tantalum and niobium metal. Metals can be obtained by reduction of pentachlorides with magnesium, sodium, hydrogen or by thermal decomposition in vacuum [24,28]. Oxides can be reduced using carbon, aluminum, calcium, magnesium [28, 537, 538] or alkali and rare earth metals [539]. 

Hydrogen Reduction of Niobium from Its Pentachloride (NiCIs) in Thermal Plasma... 

Production of niobium by H2 plasma reduction of its pentachloride can be described as... 

The degree of purification from iron can be quite high, e.g. down to 0-02 per cent of the niobium, provided the physical action of the filter is effective. Up to 5 per cent of the niobium is lost with the ferrous chloride by reduction to the trichloride (NbC. e to NbCla.is ). Some niobium is also believed to be reduced to the tetrachloride, but this remains volatile with the pentachloride. 

The oxychloride is volatile and enters the second reduction stage along with the pentachloride. At about 500°C it tends to be reduced to niobium oxide, which deposits with the trichloride, i.e. 

Information on the carbonyl chemistry of niobium and tantalum is, to date, very meager. The main difficulty appears to be the reduction of the usual pentavalent derivatives of these metals to the very low formal oxidation states of metal carbonyl derivatives. Nevertheless, the yellow anions [M(C0)6] (M = Nb, Ta) have been obtained by a method analogous to, but more difficult than, one of the preparations of the [VCCO) ]" anion. The method involves reduction of the pentachlorides with sodium metal in diglyme in the presence of high pressures of carbon monoxide (63). The niobium and tantalum derivatives are much more air-sensitive than the analogous vanadium derivative. The niobium derivative has not yet been obtained analytically pure (63). No chemistry of the [Nb(CO)J and the [Ta(CO)6] ions has been reported, even conversion to the neutral carbonyl derivatives [M(CO) (M = Nb or Ta = 1 or 2) or to the carbonyl hydride derivatives HM(CO)6 (M = Nb, Ta) still presenting unsolved problems. 

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