Editing Vanadium (section)

=== Oxyanions ===
[[File:decavanadate polyhedra.png|thumb|The [[decavanadate]] structure]]
<!-- [[File:Ammonium-metavanadate-chains-3D.png|thumb|upright|Metavanadate chains]] -->In an aqueous solution, vanadium(V) forms an extensive family of [[oxyanion]]s as established by [[Vanadium-51 nuclear magnetic resonance|<sup>51</sup>V NMR spectroscopy]].<ref name="Rehder" /> The interrelationships in this family are described by the [[predominance diagram]], which shows at least 11 species, depending on pH and concentration.<ref>{{Greenwood&Earnshaw|page=984}}</ref> The tetrahedral orthovanadate ion, {{chem|VO|4|3−}}, is the principal species present at pH 12–14. Similar in size and charge to phosphorus(V), vanadium(V) also parallels its chemistry and crystallography. [[Sodium orthovanadate|Orthovanadate]] V{{chem|O|4|3−}} is used in [[protein crystallography]]<ref>{{cite journal |last1=Sinning |first1=Irmgard |last2=Hol |first2=Wim G. J. |date=2004 |title=The power of vanadate in crystallographic investigations of phosphoryl transfer enzymes |journal=FEBS Letters |volume=577 |issue=3 |pages=315–21 |doi=10.1016/j.febslet.2004.10.022 |pmid=15556602 |s2cid=8328704 |doi-access=free|bibcode=2004FEBSL.577..315D }}</ref> to study the [[biochemistry]] of phosphate.<ref>{{cite journal |last1=Seargeant |first1=L E |last2=Stinson |first2=R A |date=1 July 1979 |title=Inhibition of human alkaline phosphatases by vanadate |journal=Biochemical Journal |volume=181 |issue=1 |pages=247–250 |doi=10.1042/bj1810247 |pmc=1161148 |pmid=486156}}</ref> Besides that, this anion also has been shown to interact with the activity of some specific enzymes.<ref>{{cite journal |last1=Crans |first1=Debbie C. |last2=Simone |first2=Carmen M. |date=9 July 1991 |title=Nonreductive interaction of vanadate with an enzyme containing a thiol group in the active site: glycerol-3-phosphate dehydrogenase |journal=Biochemistry |volume=30 |issue=27 |pages=6734–6741 |doi=10.1021/bi00241a015 |pmid=2065057}}</ref><ref>{{cite journal |last1=Karlish |first1=S. J. D. |last2=Beaugé |first2=L. A. |last3=Glynn |first3=I. M. |date=November 1979 |title=Vanadate inhibits (Na+ + K+)ATPase by blocking a conformational change of the unphosphorylated form |journal=Nature |volume=282 |issue=5736 |pages=333–335 |bibcode=1979Natur.282..333K |doi=10.1038/282333a0 |pmid=228199 |s2cid=4341480}}</ref> The tetrathiovanadate [VS<sub>4</sub>]<sup>3−</sup> is analogous to the orthovanadate ion.<ref>{{Greenwood&Earnshaw|page=988}}</ref>

At lower pH values, the monomer [HVO<sub>4</sub>]<sup>2−</sup> and dimer [V<sub>2</sub>O<sub>7</sub>]<sup>4−</sup> are formed, with the monomer predominant at a vanadium concentration of less than c. 10<sup>−2</sup>M (pV > 2, where pV is equal to the minus value of the logarithm of the total vanadium concentration/M). The formation of the divanadate ion is analogous to the formation of the [[dichromate]] ion.<ref>{{cite journal |last1=Crans |first1=Debbie C. |date=18 December 2015 |title=Antidiabetic, Chemical, and Physical Properties of Organic Vanadates as Presumed Transition-State Inhibitors for Phosphatases |journal=The Journal of Organic Chemistry |volume=80 |issue=24 |pages=11899–11915 |doi=10.1021/acs.joc.5b02229 |pmid=26544762|doi-access=free }}</ref><ref>{{cite thesis |last1=Jung |first1=Sabrina |title=Speciation of molybdenum- and vanadium-based polyoxometalate species in aqueous medium and gas-phase and its consequences for M1 structured MoV oxide synthesis |date=2018 |doi=10.14279/depositonce-7254}}</ref> As the pH is reduced, further protonation and condensation to [[vanadate|polyvanadates]] occur: at pH 4–6 [H<sub>2</sub>VO<sub>4</sub>]<sup>−</sup> is predominant at pV greater than ca. 4, while at higher concentrations trimers and tetramers are formed.<ref>{{Citation |last=Cruywagen |first=J. J. |title=Protonation, Oligomerization, and Condensation Reactions of Vanadate(V), Molybdate(vi), and Tungstate(vi) |date=1999-01-01 |url=https://www.sciencedirect.com/science/article/pii/S0898883808602706 |volume=49 |pages=127–182 |editor-last=Sykes |editor-first=A. G. |access-date=2023-04-16 |series=Advances in Inorganic Chemistry |publisher=Academic Press |language=en |doi=10.1016/S0898-8838(08)60270-6 |isbn=978-0-12-023649-7}}</ref> Between pH 2–4 [[decavanadate]] predominates, its formation from orthovanadate is represented by this condensation reaction:
:10 [VO<sub>4</sub>]<sup>3−</sup> + 24 H<sup>+</sup> → [V<sub>10</sub>O<sub>28</sub>]<sup>6−</sup> + 12 H<sub>2</sub>O

[[File:Vanadium crystal.jpg|thumb|Vanadium crystal]]
In decavanadate, each V(V) center is surrounded by six oxide [[ligand]]s.<ref name="HollemanAF" /> Vanadic acid, H<sub>3</sub>VO<sub>4</sub>, exists only at very low concentrations because protonation of the tetrahedral species [H<sub>2</sub>VO<sub>4</sub>]<sup>−</sup> results in the preferential formation of the octahedral [VO<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]<sup>+</sup> species.<ref>{{Cite book |last1=Tracey |first1=Alan S. |url=https://books.google.com/books?id=vkMGP3PiuyYC&dq=+protonation+of+the+tetrahedral+species+%5BH2VO4%5D%E2%88%92+results+in+the+preferential+formation+of+the+octahedral+%5BVO2(H2O)4%5D++species&pg=PP1 |title=Vanadium: Chemistry, Biochemistry, Pharmacology and Practical Applications |last2=Willsky |first2=Gail R. |last3=Takeuchi |first3=Esther S. |date=2007-03-19 |publisher=CRC Press |isbn=978-1-4200-4614-4 |language=en}}</ref> In strongly acidic solutions, pH&nbsp;<&nbsp;2, [VO<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]<sup>+</sup> is the predominant species, while the oxide V<sub>2</sub>O<sub>5</sub> precipitates from solution at high concentrations. The oxide is formally the [[acidic oxide|acid anhydride]] of vanadic acid. The structures of many [[vanadate]] compounds have been determined by X-ray crystallography.

[[File:VinwaterPourbaixdiagram2.svg|thumb|The [[Pourbaix diagram]] for vanadium in water, which shows the [[redox]] potentials between various vanadium species in different oxidation states<ref>{{cite journal |last1=Al-Kharafi |first1=F.M. |last2=Badawy |first2=W.A. |date=January 1997 |title=Electrochemical behaviour of vanadium in aqueous solutions of different pH |journal=Electrochimica Acta |volume=42 |issue=4 |pages=579–586 |doi=10.1016/S0013-4686(96)00202-2}}</ref>]]

Vanadium(V) forms various peroxo complexes, most notably in the active site of the vanadium-containing [[bromoperoxidase]] enzymes. The species VO(O<sub>2</sub>)(H<sub>2</sub>O)<sub>4</sub><sup>+</sup> is stable in acidic solutions. In alkaline solutions, species with 2, 3 and 4 peroxide groups are known; the last forms violet salts with the formula M<sub>3</sub>V(O<sub>2</sub>)<sub>4</sub> nH<sub>2</sub>O (M= Li, Na, etc.), in which the vanadium has an 8-coordinate dodecahedral structure.<ref>{{Greenwood&Earnshaw}}, p994.</ref><ref>{{cite book |author=Strukul, Giorgio |url=https://books.google.com/books?id=Lmt3x9CyfLgC&pg=PA128 |title=Catalytic oxidations with hydrogen peroxide as oxidant |date=1992 |publisher=Springer |isbn=978-0-7923-1771-5 |page=128}}</ref>