Vanadium Colours (Making Vanadyl sulfate Part 1)
Channel: EnTroPy
Date: 26/08/2014

Vanadyl sulfate is most commonly obtained by reduction of vanadium pentoxide with sulfur dioxide:

V2O5 + 7 H2O + SO2 + H2SO4 → 2 [V(O)(H2O)4]SO4
From aqueous solution, the salt crystallizes as the pentahydrate, the fifth water is not bound to the metal in the solid. Viewed as a coordination complex, the ion is octahedral, with oxo, four equatorial water ligands, and a monodentate sulfate.[1] The V=O bond distance is 160 pm in length, about 50 pm shorter than the V–OH2 bonds. In solution, the sulfate ion dissociates rapidly.

Being widely available, vanadyl sulfate is a common precursor to other vanadyl derivatives, such as vanadyl acetylacetonate:[3]

[V(O)(H2O)4]SO4 + 2C5H8O2 + Na2CO3 → [V(O)(C5H7O2)2] + Na2SO4 + 5 H2O + CO2
In acidic solution, oxidation of vanadyl sulfate gives yellow-coloured vanadyl(V) derivatives. Reduction, e.g. by zinc, gives vanadium(III) and vanadium(II) derivatives, which are characteristically green and violet, respectively.