In chemistry, a vanadate is an anionic

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...

of vanadium. Often vanadate refers to oxoanions of vanadium, most of which exist in its highest

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

of +5. The complexes and are referred to as hexacyanovanadate(III) and nonachlorodivanadate(III), respectively. A simple vanadate ion is the tetrahedral orthovanadate anion, (which is also called vanadate(V)), which is present in e.g.

sodium orthovanadate Sodium orthovanadate is the inorganic compound with the chemical formula . It forms a dihydrate . Sodium orthovanadate is a salt of the oxyanion. It is a colorless, water-soluble solid. Synthesis and structure Sodium orthovanadate is produced by ...

and in solutions of in strong base ( pH > 13). Conventionally this ion is represented with a single double bond, however this is a resonance form as the ion is a regular tetrahedron with four equivalent oxygen atoms. Additionally a range of polyoxovanadate ions exist which include discrete ions and "infinite" polymeric ions. There are also vanadates, such as rhodium vanadate, , which has a statistical

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

structure where the and ions randomly occupy the positions in the rutile lattice, that do not contain a lattice of cations and balancing vanadate anions but are mixed oxides. In chemical nomenclature when vanadate forms part of the name, it indicates that the compound contains an anion with a central vanadium atom, e.g. ammonium hexafluorovanadate is a common name for the compound with the

IUPAC name In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among the possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for choo ...

of ammonium hexafluoridovanadate(III).

Examples of oxovanadate ions

Some examples of discrete ions are * "orthovanadate", tetrahedral. * "pyrovanadate", corner-shared tetrahedra, similar to the Dichromate ion, dichromate ion *, cyclic with corner-shared tetrahedra *, cyclic with corner-shared tetrahedra *, corner shared tetrahedra *, ring. * "decavanadate", edge- and corner-shared octahedra * *, fused octahedra * Some examples of polymeric "infinite" ions are * in e.g. , sodium metavanadate * in In these ions vanadium exhibits tetrahedral, square pyramidal and octahedral coordination. In this respect vanadium shows similarities to tungstate and molybdate, whereas chromium however has a more limited range of ions.

Aqueous solutions

Dissolution of vanadium pentoxide in strongly basic aqueous solution gives the colourless ion. On acidification, this solution's colour gradually darkens through orange to red at around pH 7. Brown hydrated V2O5 precipitates around pH 2, redissolving to form a light yellow solution containing the ion. The number and identity of the oxyanions that exist between pH 13 and 2 depend on pH as well as concentration. For example, protonation of vanadate initiates a series of Condensation reaction, condensations to produce polyoxovanadate ions: *pH 9–12: , *pH 4–9: , , *pH 2–4: ,

Pharmacological properties

Vanadate is a potent inhibitor of certain plasma membrane ATPases, such as Na+/K+-ATPase, Na⁺/K⁺-ATPase and Ca²⁺-ATPase (Plasma membrane Ca2+ ATPase, PMCA). Acting as a transition-state analog of phosphate, vanadate undergoes nucleophillic attack by water during phosphoryl transfer, essentially "trapping" P-type ATPases in their phosphorylated E2 state. However, it does not inhibit other ATPases, such as SERCA (sarco/endoplasmic reticulum Ca²⁺-ATPase), actomyosin ATPase and mitochondrial ATPase.

References

{{Hydrogen compounds Vanadates, Transition metal oxyanions Oxometallates