Niobium oxyhalides

When dewed from the point of view of the Werner co-ordination theory, it is observed that the co-ordination number seven is frequent in the double fluorides as well as in the niobium oxyhalides. Many members of the series 2R F.NbFs or [NbFJRa, and of the series... 

Niobium Halides and Oxyhalides. AH possible haUdes of pentavalent niobium are known and preparations of lower valent haUdes generally start with the pentahaUde. Ease of reduction decreases from iodide to fluoride. 

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. 

Hala, J. Halides, Oxyhalides and Salts of Halogen Complexes of Titanium, Zirconium, Hafnium, Vanadium, Niobium and Tantalum, Vol, 40, Elsevier Science, New York, NY, 1989. 

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. 

Niobium(v) and Tantalum(v).—Halides, Oxyhalides and Related Compounds. The ability of TaFj to act as a fluoride ion acceptor in anhydrous HF has been exploited in the preparation of salts of the AsH, HjS, and PH ions... 

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

Hala J (1989) Halides, oxyhalides and salts of halogen complexes of titanium, zirconium, hafnium, vanadium, niobium and tantalum. lUPAC, Blackwell, London... 

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