Vanadium compounds

[2] Ammonium vanadate(V) (NH4VO3) can be successively reduced with elemental zinc to obtain the different colors of vanadium in these four oxidation states.

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.

[2] In aqueous solution, vanadium(V) forms an extensive family of oxyanions as established by 51V NMR spectroscopy.

[3] The interrelationships in this family are described by the predominance diagram, which shows at least 11 species, depending on pH and concentration.

Vanadium(V) forms various peroxo complexes, most notably in the active site of the vanadium-containing bromoperoxidase enzymes.

In alkaline solutions, species with 2, 3 and 4 peroxide groups are known; the last forms violet salts with the formula M3V(O2)4 nH2O (M= Li, Na, etc.

Akin to POCl3, they are volatile, adopt tetrahedral structures in the gas phase, and are Lewis acidic.

Vanadium ion is rather large and some complexes achieve coordination numbers greater than 6, as is the case in [V(CN)7]4−.

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.

[14] The coordination chemistry of V5+ is dominated by the relatively stable dioxovanadium coordination complexes 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.

[16] Organovanadium compounds find only minor use as reagents in organic synthesis but are significant for polymer chemistry as catalysts.

These catalysts are generated in situ by treating soluble coordination complexes such as vanadium(III) acetylacetonate with organoaluminium activators.