The preparation and properties of niobium(IV) compounds. I. Some niobium(IV) halides and their pyridine adducts

Article abstract of DOI:10.1021/ic50007a029

Reaction of NbBr₅ and niobium metal in a sealed tube under a temperature gradient from 410 to 350° gave NbBr₄ in good yields. However, an increase in the higher temperature from 410 to 450° was sufficient to eliminate NbBr₄ as a product and cause deposition of a lower bromide. The halides NbCl₄ and NbBr₄ are isomorphous solids of orthorhombic structure and lattice constants a = 8.12, b = 8.88, c = 6.84 A?. and a = 8.60, b = 9.31, c = 7.19 A?., respectively; both solids are diamagnetic over the range -195 to 25°. Formation of the tetrahalodi-(pyridine)-niobium(IV) complexes resulted from the reactions of the pure tetrahalides (Cl, Br, I) with pyridine at room temperature; at elevated temperatures a second form of NbBr₄(py)₂ crystallized from pyridine. Evidence bearing on the structure of the pyridine adducts was obtained from conductance, spectral, and magnetic susceptibility measurements. The complexes are paramagnetic and exhibit moments much lower than the spin-only value for one magnetic electron; the spectra of solutions in pyridine show intense bands in the visible region which have been attributed to charge transfer transitions.