Vanadate

A simple vanadate ion is the tetrahedral orthovanadate anion, VO3−4 (which is also called vanadate(V)), which is present in e.g. sodium orthovanadate and in solutions of V₂O₅ in strong base (pH > 13). Conventionally this ion is represented with a single double bond, however this is a resonance form as the ion is a regular tetrahedron with four equivalent oxygen atoms.

Additionally a range of polyoxovanadate ions exist which include discrete ions and "infinite" polymeric ions. There are also vanadates, such as rhodium vanadate, RhVO₄, which has a statistical rutile structure where the Rh³⁺ and V⁵⁺ ions randomly occupy the Ti⁴⁺ positions in the rutile lattice, that do not contain a lattice of cations and balancing vanadate anions but are mixed oxides.

In chemical nomenclature when vanadate forms part of the name, it indicates that the compound contains an anion with a central vanadium atom, e.g. ammonium hexafluorovanadate is a common name for the compound (NH₄)₃VF₆ with the IUPAC name of ammonium hexafluoridovanadate(III).

Examples of oxovanadate ions

Some examples of discrete ions are

• VO₄³⁻ "orthovanadate", tetrahedral.
• V₂O₇⁴⁻ "pyrovanadate", corner-shared VO₄ tetrahedra, similar to the dichromate ion
• V₃O₉³⁻, cyclic with corner-shared VO₄ tetrahedra
• V₄O₁₂⁴⁻, cyclic with corner-shared VO₄ tetrahedra
• V₅O₁₄³⁻, corner shared VO₄ tetrahedra
• V₆O₁₈⁶⁻, ring.
• V₁₀O₂₈⁶⁻ "decavanadate", edge- and corner-shared VO₆ octahedra
• V₁₂O₃₂⁴⁻
• V₁₃O₃₄³⁻, fused VO₆ octahedra
• V₁₈O₄₂¹²⁻

Some examples of polymeric "infinite" ions are

• [VO₃]_nⁿ⁻ in e.g. NaVO₃, sodium metavanadate
• [V₃O₈]_nⁿ⁻ in CaV₆O₁₆

In these ions vanadium exhibits tetrahedral, square pyramidal and octahedral coordination. In this respect vanadium shows similarities to tungstate and molybdate, whereas chromium however has a more limited range of ions.