Niobium bromides Reduction

Oxidation-Reduction Titrations. The extent of reduction resulting from reaction of niobium (V) chloride and bromide with pyridine was determined by indirect titration of crude reaction mixtures with standard ammonium tetrasulfato-cerate(IV) solution. Samples were stirred overnight in a stoppered flask with an excess of iron (III) ammonium sulfate. Any iron (II) formed by reaction with the niobium complex mixture was then titrated with the standard tetrasulfato-cerate(IV) solution using ferroin as indicator. Results of these determinations are given in Table III. 

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. 

Weight gain data and oxidation-reduction titers (Table II) for the niobium (V) chloride and bromide reaction products both indicated the reduction of niobium (V) to niobium (IV). The niobium (IV) adducts were separated by washing the crude reaction mixtures with anhydrous acetonitrile. This solvent removed the various organic products of the initial reaction plus any unreduced niobium compounds. Analysis of the washed products gave ratios of Nb X py of 1 4 2 and agreed with analyses for samples of NbCl py2 and NbBr4 py2 which... 

It was thus shown that the tetrahalodi(pyridine)niobium(IV) complexes were the reduction products of the reactions of niobium(V) chloride and niobium (V) bromide with pyridine. 

Similarly, it was concluded that in the reduction reaction of niobium(V) bromide with pyridine the major products were tetrabromodi (pyridine )niobium-(IV), pyridinium bromide, and l-(4-pyridyl) pyridinium bromide. Oxidation-reduction titrations indicated approximately 90% reduction. The remaining 10% of niobium was assumed to be present as pentabromo(pyridine)niobium(V). The over-all reaction was indicated to be ... 

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