Editing Group 5 element (section)

==== Oxyanions ====

[[File:decavanadate polyhedra.png|thumb|The [[decavanadate]] structure]]
<!-- [[File:Ammonium-metavanadate-chains-3D.png|thumb|upright|Metavanadate chains]] -->In 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">{{cite book |doi=10.1016/S0066-4103(07)62002-X|title=Vanadium-51 NMR|series=Annual Reports on NMR Spectroscopy|year=2007|last1=Rehder|first1=D.|last2=Polenova|first2=T.|last3=Bühl|first3=M.|volume=62|pages=49–114|isbn=9780123739193}}</ref> 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|volume= 577|issue= 3|doi= 10.1016/j.febslet.2004.10.022|pmid= 15556602|date= 2004|title= The power of vanadate in crystallographic investigations of phosphoryl transfer enzymes|first1= Irmgard|last1= Sinning|journal= FEBS Letters|last2= Hol|first2= Wim G. J.|pages= 315–21|s2cid= 8328704|doi-access= free|bibcode= 2004FEBSL.577..315D}}</ref> to study the [[biochemistry]] of phosphate.<ref>{{cite journal|volume= 181|pmc= 1161148|date= 1979|title= Inhibition of human alkaline phosphatases by vanadate|first= Lorne E.|last= Seargeant|author2=Stinson, Robert A. |journal= Biochemical Journal|pmid=486156|issue=1|pages= 247–50|doi= 10.1042/bj1810247}}</ref> Beside that, this anion also has been shown to interact with activity of some specific enzymes.<ref>{{Cite journal |last1=Crans |first1=Debbie C. |last2=Simone |first2=Carmen M. |date=1991-07-09 |title=Nonreductive interaction of vanadate with an enzyme containing a thiol group in the active site: glycerol-3-phosphate dehydrogenase |url=https://pubs.acs.org/doi/abs/10.1021/bi00241a015 |journal=Biochemistry |language=en |volume=30 |issue=27 |pages=6734–6741 |doi=10.1021/bi00241a015 |pmid=2065057 |issn=0006-2960|url-access=subscription }}</ref><ref>{{Cite journal |last1=Karlish |first1=S. J. D. |last2=Beaugé |first2=L. A. |last3=Glynn |first3=I. M. |date=Nov 1979 |title=Vanadate inhibits (Na+ + K+)ATPase by blocking a conformational change of the unphosphorylated form |url=https://www.nature.com/articles/282333a0 |journal=Nature |language=en |volume=282 |issue=5736 |pages=333–335 |doi=10.1038/282333a0 |pmid=228199 |bibcode=1979Natur.282..333K |s2cid=4341480 |issn=1476-4687|url-access=subscription }}</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 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. 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. Between pH 2–4 [[decavanadate]] predominates, though its formation from orthovanadate is optimized at pH 4–7, represented by this reaction:<ref name="one">{{cite book |author1=Johnson, G. |title=Inorganic Syntheses |author2=Murmann, R. K. |date=1979 |isbn=978-0-471-04542-7 |volume=19 |pages=140–145 |chapter=Sodium and Ammonium Decayanadates(V) |doi=10.1002/9780470132500.ch32}}</ref>
:{{Chem2|10 Na3[VO4] + 24 HOAc → Na6[V10O28] + 12 H2O + 24 NaOAc}}

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. 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.<ref>{{Cite journal |last=Sadoc |first=Aymeric |last2=Messaoudi |first2=Sabri |last3=Furet |first3=Eric |last4=Gautier |first4=Régis |last5=Le Fur |first5=Eric |last6=le Pollès |first6=Laurent |last7=Pivan |first7=Jean-Yves |date=2007-06-01 |title=Structure and Stability of VO 2 + in Aqueous Solution: A Car−Parrinello and Static ab Initio Study |url=https://pubs.acs.org/doi/10.1021/ic0614519 |journal=Inorganic Chemistry |language=en |volume=46 |issue=12 |pages=4835–4843 |doi=10.1021/ic0614519 |issn=0020-1669|url-access=subscription }}</ref> 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.<ref>{{Cite journal |last=Davies |first=Douglas R. |last2=Hol |first2=Wim G.J. |date=2004-11-19 |title=The power of vanadate in crystallographic investigations of phosphoryl transfer enzymes |url=https://febs.onlinelibrary.wiley.com/doi/10.1016/j.febslet.2004.10.022 |journal=FEBS Letters |language=en |volume=577 |issue=3 |pages=315–321 |doi=10.1016/j.febslet.2004.10.022 |issn=0014-5793}}</ref>

[[File:VinwaterPourbaixdiagram2.svg|thumb|right|The [[Pourbaix diagram]] for vanadium in water, which shows the [[redox]] potentials between various vanadium species in different oxidation states.<ref>{{cite journal|journal= Electrochimica Acta|volume= 42|date= 1997|pages= 579–586|doi= 10.1016/S0013-4686(96)00202-2|title= Electrochemical behavior of vanadium in aqueous solutions of different pH|first= F. M.|last= Al-Kharafi|author2=Badawy, W. A. |issue= 4}}</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|date=1992|url=https://books.google.com/books?id=Lmt3x9CyfLgC&pg=PA128|page=128|title=Catalytic oxidations with hydrogen peroxide as oxidant|author=Strukul, Giorgio|publisher=Springer|isbn=978-0-7923-1771-5}}</ref>

Niobates are generated by dissolving the pentoxide in [[Base (chemistry)|basic]] [[hydroxide]] solutions or by melting it in alkali metal oxides. Examples are [[lithium niobate]] ({{chem2|LiNbO3}}) and lanthanum niobate ({{chem2|LaNbO4}}). In the lithium niobate is a trigonally distorted [[Perovskite (structure)|perovskite]]-like structure, whereas the lanthanum niobate contains lone {{chem|NbO|4|3-}} ions.<ref name="HollemanAF" />

Tantalates, compounds containing [TaO<sub>4</sub>]<sup>3−</sup> or [TaO<sub>3</sub>]<sup>−</sup> are numerous. [[Lithium tantalate]] (LiTaO<sub>3</sub>) adopts a perovskite structure. [[Lanthanum]] tantalate (LaTaO<sub>4</sub>) contains isolated {{chem|TaO|4|3−}} tetrahedra.<ref name="HollemanAF" />