The vanadyl ion or oxovanadium(IV) cation, VO<sup>2+</sup>, is a functional group that is common in the coordination chemistry of vanadium. Complexes containing this functional group are characteristically blue or purple and paramagnetic. A triple bond is proposed to exist between the V<sup>4+</sup> and O<sup>2âÂÂ</sup> centers. The description of the bonding in the vanadyl ion was central to the development of modern ligand-field theory.
Cavansite and pentagonite are vanadyl-containing minerals.
VO<sup>2+</sup>, often in an ionic pairing with sodium (NaH<sub>2</sub>VO<sub>4</sub>), is the second most abundant transition metal in seawater, with its concentration only being exceeded by molybdenum. In the ocean the average concentration is 30 nM. Some mineral water springs also contain the ion in high concentrations. For example, springs near Mount Fuji often contain as much as 54 üg per liter.