Editing Vanadium (section)

== Compounds ==
{{Main|Vanadium compounds}}
[[File:Vanadiumoxidationstates.jpg|thumb|left|upright|From left: [V(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> (lilac), [V(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup> (green), [VO(H<sub>2</sub>O)<sub>5</sub>]<sup>2+</sup> (blue) and [VO(H<sub>2</sub>O)<sub>5</sub>]<sup>3+</sup> (yellow)]]
The chemistry of vanadium is noteworthy for the accessibility of the four adjacent [[oxidation state]]s 2–5. In an [[metal ions in aqueous solution|aqueous solution]], vanadium forms [[metal aquo complex]]es of which the colors are lilac [V(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>, green [V(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup>, blue [VO(H<sub>2</sub>O)<sub>5</sub>]<sup>2+</sup>, yellow-orange oxides [VO(H<sub>2</sub>O)<sub>5</sub>]<sup>3+</sup>, the formula for which depends on pH. Vanadium(II) compounds are reducing agents, and vanadium(V) compounds are oxidizing agents. Vanadium(IV) compounds often exist as [[vanadyl ion|vanadyl]] derivatives, which contain the VO<sup>2+</sup> center.<ref name="HollemanAF" />

[[Ammonium metavanadate|Ammonium vanadate(V)]] (NH<sub>4</sub>VO<sub>3</sub>) can be successively reduced with elemental [[zinc]] to obtain the different colors of vanadium in these four oxidation states. Lower oxidation states occur in compounds such as [[vanadium hexacarbonyl|V(CO)<sub>6</sub>]], {{chem|[V(CO)|6|]|-}} and substituted derivatives.<ref name="HollemanAF" />

[[Vanadium(V) oxide|Vanadium pentoxide]] is a commercially important catalyst for the production of sulfuric acid, a reaction that exploits the ability of vanadium oxides to undergo redox reactions.<ref name="HollemanAF" />

The [[vanadium redox battery]] utilizes all four oxidation states: one electrode uses the +5/+4 couple and the other uses the +3/+2 couple. Conversion of these oxidation states is illustrated by the reduction of a strongly acidic solution of a vanadium(V) compound with zinc dust or amalgam. The initial yellow color characteristic of the pervanadyl ion [VO<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]<sup>+</sup> is replaced by the blue color of [VO(H<sub>2</sub>O)<sub>5</sub>]<sup>2+</sup>, followed by the green color of [V(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup> and then the violet color of [V(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>.<ref name="HollemanAF" /> Another potential vanadium battery based on VB<sub>2</sub> uses multiple oxidation state to allow for 11 electrons to be released per VB<sub>2</sub>, giving it higher energy capacity by order of compared to Li-ion and gasoline per unit volume.<ref name=":0">{{Cite journal |last1=Licht |first1=Stuart |last2=Wu |first2=Huiming |last3=Yu |first3=Xingwen |last4=Wang |first4=Yufei |date=2008-07-11 |title=Renewable highest capacity VB2/air energy storage |url=https://pubs.rsc.org/en/content/articlelanding/2008/cc/b807929c |journal=Chemical Communications |language=en |issue=28 |pages=3257–3259 |doi=10.1039/B807929C |pmid=18622436 |issn=1364-548X}}</ref> VB<sub>2</sub> batteries can be further enhanced as air batteries, allowing for even higher energy density and lower weight than lithium battery or gasoline, even though recharging remains a challenge. <ref name=":0" />

=== 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>

=== Halide derivatives ===
Twelve binary [[halides]], compounds with the formula VX<sub>n</sub> (n=2..5), are known.<ref name="G&E989">{{Greenwood&Earnshaw2nd|page=989}}</ref> VI<sub>4</sub>, VCl<sub>5</sub>, VBr<sub>5</sub>, and VI<sub>5</sub> do not exist or are extremely unstable. In combination with other reagents, [[vanadium(IV) chloride|VCl<sub>4</sub>]] is used as a catalyst for the polymerization of [[diene]]s. Like all binary halides, those of vanadium are [[Lewis acid]]ic, especially those of V(IV) and V(V).<ref name="G&E989" /> Many of the halides form octahedral complexes with the formula VX<sub>''n''</sub>L<sub>6−''n''</sub> (X= halide; L= other ligand).

Many vanadium [[oxyhalide]]s (formula VO<sub>m</sub>X<sub>n</sub>) are known.<ref>{{Greenwood&Earnshaw|page=993}}</ref> The oxytrichloride and oxytrifluoride ([[vanadium oxytrichloride|VOCl<sub>3</sub>]] and [[Vanadium(V) oxytrifluoride|VOF<sub>3</sub>]]) are the most widely studied. Akin to POCl<sub>3</sub>, they are volatile,<ref>{{cite journal |last1=Flesch |first1=Gerald D. |last2=Svec |first2=Harry J. |date=1 August 1975 |title=Thermochemistry of vanadium oxytrichloride and vanadium oxytrifluoride by mass spectrometry |journal=Inorganic Chemistry |volume=14 |issue=8 |pages=1817–1822 |doi=10.1021/ic50150a015}}</ref> adopt tetrahedral structures in the gas phase, and are Lewis acidic.<ref>{{cite journal |last1=Iqbal |first1=Javed |last2=Bhatia |first2=Beena |last3=Nayyar |first3=Naresh K. |date=March 1994 |title=Transition Metal-Promoted Free-Radical Reactions in Organic Synthesis: The Formation of Carbon-Carbon Bonds |journal=Chemical Reviews |volume=94 |issue=2 |pages=519–564 |doi=10.1021/cr00026a008}}</ref>

=== Coordination compounds ===
[[File:Vanadyl-acetylacetonate-from-xtal-3D-balls.png|thumb|A [[ball-and-stick model]] of [[vanadyl acetylacetonate|VO(O<sub>2</sub>C<sub>5</sub>H<sub>7</sub>)<sub>2</sub>]]]]
Complexes of vanadium(II) and (III) are reducing, while those of V(IV) and V(V) are oxidants. The vanadium ion is rather large and some complexes achieve coordination numbers greater than 6, as is the case in [V(CN)<sub>7</sub>]<sup>4−</sup>. Oxovanadium(V) also forms 7 coordinate coordination complexes with tetradentate ligands and peroxides and these complexes are used for oxidative brominations and thioether oxidations. The coordination chemistry of V<sup>4+</sup> is dominated by the [[vanadyl]] center, VO<sup>2+</sup>, which binds four other ligands strongly and one weakly (the one trans to the vanadyl center). An example is [[vanadyl acetylacetonate]] (V(O)(O<sub>2</sub>C<sub>5</sub>H<sub>7</sub>)<sub>2</sub>). In this complex, the vanadium is 5-coordinate, distorted square pyramidal, meaning that a sixth ligand, such as pyridine, may be attached, though the [[association constant]] of this process is small. Many 5-coordinate vanadyl complexes have a trigonal bipyramidal geometry, such as VOCl<sub>2</sub>(NMe<sub>3</sub>)<sub>2</sub>.<ref>{{Greenwood&Earnshaw2nd|page=995}}</ref> The coordination chemistry of V<sup>5+</sup> is dominated by the relatively stable dioxovanadium coordination complexes<ref>{{cite thesis |last1=Geiser |first1=Jan Nicholas |title=Development of an improved state-of-charge sensor for the all-vanadium redox flow battery |date=2019 |doi=10.22028/D291-29229}}</ref> which are often formed by aerial oxidation of the vanadium(IV) precursors indicating the stability of the +5 oxidation state and ease of interconversion between the +4 and +5 states.<ref>{{cite journal |last1=Nica |first1=Simona |last2=Rudolph |first2=Manfred |last3=Görls |first3=Helmar |last4=Plass |first4=Winfried |date=April 2007 |title=Structural characterization and electrochemical behavior of oxovanadium(V) complexes with N-salicylidene hydrazides |journal=Inorganica Chimica Acta |volume=360 |issue=5 |pages=1743–1752 |doi=10.1016/j.ica.2006.09.018}}</ref>

=== Organometallic compounds ===
{{Main|Organovanadium chemistry}}

The organometallic chemistry of vanadium is well{{en dash}}developed. [[Vanadocene dichloride]] is a versatile starting reagent and has applications in organic chemistry.<ref name="wilkinson">{{cite journal |last1=Wilkinson |first1=G. |last2=Birmingham |first2=J. M. |date=September 1954 |title=Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta |journal=Journal of the American Chemical Society |volume=76 |issue=17 |pages=4281–4284 |doi=10.1021/ja01646a008|bibcode=1954JAChS..76.4281W }}</ref> [[Vanadium carbonyl]], V(CO)<sub>6</sub>, is a rare example of a paramagnetic [[metal carbonyl]]. Reduction yields V{{chem|(CO)|6|−}} ([[isoelectronic]] with [[hexacarbonylchromium|Cr(CO)<sub>6</sub>]]), which may be further reduced with sodium in liquid ammonia to yield V{{chem|(CO)|5|3−}} (isoelectronic with Fe(CO)<sub>5</sub>).<ref>{{cite journal |last1=Bellard |first1=S. |last2=Rubinson |first2=K. A. |last3=Sheldrick |first3=G. M. |date=15 February 1979 |title=Crystal and molecular structure of vanadium hexacarbonyl |journal=Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry |volume=35 |issue=2 |pages=271–274 |doi=10.1107/S0567740879003332|bibcode=1979AcCrB..35..271B }}</ref><ref>{{cite book |last=Elschenbroich |first=C. |title=Organometallics: A Concise Introduction |author2=Salzer A. |date=1992 |publisher=Wiley-VCH |isbn=978-3-527-28165-7}}</ref>