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In chemistry, a vanadate is a compound containing an oxoanion of vanadium generally in its highest oxidation state of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO3−
4 anion, which is present in e.g. sodium orthovanadate and in solutions of V2O5 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.
Contents
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 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 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 (NH4)3VF6 with the IUPAC name of ammonium hexafluoridovanadate(III).
Examples of vanadate ions
Some examples of discrete ions are
4 "orthovanadate", tetrahedral.
2O4−
7 "pyrovanadate", corner-shared VO4 tetrahedra, similar to the dichromate ion
3O3−
9, cyclic with corner-shared VO4 tetrahedra
4O4−
12, cyclic with corner-shared VO4 tetrahedra
5O3−
14, corner shared VO4 tetrahedra
10O6−
28 "decavanadate", edge- and corner-shared VO6 octahedra
12O4−
32
13O3−
34, fused VO6 octahedra
18O12−
42
Some examples of polymeric “infinite” ions are
n in e.g. NaVO3, sodium metavanadate
n in CaV6O16
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 VO3−
4 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 pH as well as concentration. For example, protonation of vanadate initiates a series of condensations to produce polyoxovanadate ions:
4, V
2O4−
7
2VO−
4, V
4O4−
12, HV
10O5−
28
2V
10O4−
28
Pharmacological properties
Vanadate is a potent inhibitor of certain plasma membrane ATPases, such as Na+/K+-ATPase and Ca2+-ATPase (PMCA). However, it does not inhibit other ATPases, such as SERCA (sarco/endoplasmic reticulum Ca2+-ATPase), actomyosin ATPase and mitochondrial ATPase. Aureliano, Manuel; Crans, Debbie C. (2009). "Decavanadate and oxovanadates: Oxometalates with many biological activities". Journal Inorganic Biochemistry 103: 536–546. doi:10.1016/j.jinorgbio.2008.11010.