Vanadium(IV) oxide sulfate hydrate, 97%

Vanadyl(IV) sulfate describes a collection of inorganic compounds of vanadium with the formula , VOSO4(H2O)x where 0≤x≤6. The pentahydrate is common. This hygroscopic blue solid is one of the most common sources of vanadium in the laboratory, reflecting its high stability. It features the vanadyl ion, VO2+, which has been called the "most stable diatomic ion." Vanadyl sulfate is an intermediate in the extraction of vanadium from petroleum residues, a one commercial source of vanadium.

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. The trihydrate has also been examined by crystallography. A hexahydrate exists below 13.6 °C (286.8 K). Two polymorphs of anhydrous VOSO4 are known. The V=O bond distance is 160 pm, 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:

[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.