Editing Vanadium (section)

=== 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>