In chemistry, a vanadate is a compound containing an oxoanion of vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

 generally in its highest oxidation state

Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

 of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO₄³⁻ anion, which is present in e.g. sodium orthovanadate

Sodium orthovanadate

Sodium orthovanadate is the chemical compound Na3VO4 and contains the tetrahedral VO43−. It is an inhibitor of protein tyrosine phosphatases, alkaline phosphatases and a number of ATPases, most likely acting as a phosphate analogue...

 and in solutions of V₂O₅ in strong base (pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 > 13 ). Conventionally this ion is represented with a single double bond, however this is a resonance form

Resonance (chemistry)

In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula...

 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, RhVO₄, which has a statistical rutile

Titanium dioxide

Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 structure where the Rh³⁺ and V⁵⁺ ions randomly occupy the Ti⁴⁺ positions in the rutile lattice, that do not contain a lattice of cations and balancing vanadate anions but are mixed oxide

Mixed oxide

In chemistry, a mixed oxide is a somewhat informal name for an oxide that contains more than one chemical element in its cation, or of a single element cation that has atoms in several states of oxidation....

s.

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 (NH₄)₃VF₆ with the IUPAC name

IUPAC nomenclature of inorganic chemistry 2005

The Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005, commonly known as The Red Book, is a collection of rules for naming inorganic compounds, as recommended by the IUPAC.- Summary :...

 of ammonium hexafluoridovanadate(V).

Examples of vanadate ions

Some examples of discrete ions are

• VO₄³⁻ "orthovanadate", tetrahedral.
• V₂O₇⁴⁻ "pyrovanadate", corner shared VO₄ tetrahedra similar to dichromate
  Chromate
  Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.- Chemical properties :...
  
   ion
• V₃O₉³⁻ cyclic with corner shared VO₄ tetrahedra
• V₄O₁₂⁴⁻ cyclic with corner shared VO₄ tetrahedra
• V₅O₁₄³⁻ corner shared VO₄ tetrahedra
• V₁₀O₂₈⁶⁻ "decavanadate", edge and corner shared VO₆ octahedra
• V₁₂O₃₂⁴⁻
• V₁₃O₃₄³⁻ fused VO₆ octahedra
• V₁₈O₄₂¹²⁻

Some examples of polymeric “infinite” ions are

• [VO₃]_nⁿ⁻ in e.g. NaVO₃, sodium metavanadate
• [V₃O₈]_nⁿ⁻ in CaV₆O₁₆

metavanadate chains	V5O14	decavanadate ion

In these ions vanadium exhibits tetrahedral, square pyramidal and octahedral coordination. In this respect vanadium shows similarities to W

Tungstate

In chemistry a tungstate is a compound that contains an oxoanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is WO42−, "orthotungstate"...

 and Mo

Molybdate

In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state.The...

, chromium however has a more limited range of ions.

Aqueous solutions

Dissolution of vanadium pentoxide in strongly basic aqueous solution gives the colourless VO₄^3– 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 [VO₂(H₂O)₄]⁺ ion. The number and identity of the oxyanions that exist between pH 13 and 2 depend on as well as concentration. For example, protonation of vanadate initiates a series of condensation

Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...

s to produce polyoxovanadate ions:

• pH 9–12; HVO₄²⁻, V₂O₇⁴⁻
• pH 4–9; H₂VO₄⁻, V₄O₁₂⁴⁻, HV₁₀O₂₈⁵⁻
• pH 2–4; H₃VO₄, H₂V₁₀O₂₈⁴⁻