Vanadium(III) bromide

Preparation

VBr3 has been prepared by treatment of vanadium tetrachloride with hydrogen bromide: ::2 VCl4 + 8 HBr → 2 VBr3 + 8 HCl + Br2 The reaction proceeds via the unstable vanadium(IV) bromide (VBr4), which releases Br2 near room temperature.

It is also possible to prepare vanadium(III) bromide by reacting bromine with vanadium or ferrovanadine:

:: 2 V + 3 Br2 → 2 VBr3 ::2 VFe + 6 Br2 → 2 VBr3 + FeBr3

Properties

Physical

Vanadium(III) bromide is present in the form of black, leafy, very hygroscopic crystals with a sometimes greenish sheen. It is soluble in water with green color. Its crystal structure is isotypic to that of vanadium(III) chloride with space group Rc (space group no. 167), a = 6.400 Å, c = 18.53 Å. When heated to temperatures of around 500 °C, a violet gas phase is formed, from which, under suitable conditions, red vanadium(IV) bromide can be separated by rapid cooling, which decomposes at −23 °C.

Chemical

Like vanadium(III) chloride, vanadium(III) bromide forms red-brown soluble complexes with dimethoxyethane and THF, such as mer-VBr3(THF)3.

Aqueous solutions prepared from VBr3 contain the cation trans-[VBr2(H2O)4]+. Evaporation of these solutions give the salt trans-[VBr2(H2O)4]Br.(H2O)2.

References

References

1. (1993). "Low-Temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". J. Chem. Soc., Dalton Trans..
2. Brauer, Georg. (1975). "Handbuch der präparativen anorganischen Chemie Volume 3". Enke.
3. G. W. A. Fowles, G. W. A.; Greene, P. T.; Lester, T. E. "Ether Complexes of Tervalent Titanium and Vanadium" J. Inorg, Nucl. Chem., 1967. Vol. 29. pp. 2365 to 2370.
4. (1975). "Crystal and Molecular Structures of Aquahalogenovanadium(III) Complexes. Part I. X-Ray Crystal Structure of ''trans''-Tetrakisaquadibromo-Vanadium(III) Bromide Dihydrate and the Isomorphous Chloro- Compound". Journal of the Chemical Society, Dalton Transactions.