Vanadate

 ( Transition Metal Oxyanions ) 

In chemistry, a vanadate is an anionic coordination complex of vanadium. Often vanadate refers to oxoanions of vanadium, most of which exist in its highest oxidation state 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 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 titanium dioxide structure where the and ions randomly occupy the positions in the rutile lattice,Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications that do not contain a lattice of cations and balancing vanadate anions but are .

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 of ammonium hexafluoridovanadate(III).

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Examples of oxovanadate ions Some examples of discrete ions are

• "orthovanadate", tetrahedral.
• "pyrovanadate", corner-shared tetrahedra, similar to the Dichromate ion ion
• , cyclic with corner-shared tetrahedra Supplementary Information.
• , 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.

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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 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 condensations to produce polyoxovanadate ions:

• pH 9–12: ,
• pH 4–9: , ,
• pH 2–4: ,

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Pharmacological properties

Vanadate is a potent inhibitor of certain plasma membrane , such as Na⁺/K⁺-ATPase and Ca²⁺-ATPase (PMCA). Acting as a transition-state analog of phosphate, vanadate undergoes nucleophillic attack by water during phosphoryl transfer, essentially "trapping" in their phosphorylated E2 state. It also inhibits skeletal muscle actomyosin MgATPase activity and calcium activated force generation by actomyosin in the intact skeletal muscle contractile apparatus. However, it does not inhibit other ATPases, such as SERCA (sarco/endoplasmic reticulum Ca²⁺-ATPase) or mitochondrial ATPase.

Categories: Transition Metal Oxyanions, Oxometallates

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