Vanadyl
The vanadyl or oxovanadium(IV) cation, VO2+, is a blue-coloured vanadium oxocation at an oxidation state of +4. It is one of the most stable diatomic ions known and forms a wide range of complexes.
VO2+, often in an ionic pairing with sodium (Na+H2VO−4), 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 μg per liter.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN .
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