orthoniobate

Orthoniobate refers to the tetra-oxo niobate(V) anion, NbO4^3−. In this ion, niobium is in the +5 oxidation state and is coordinated by four oxide ligands, producing a roughly tetrahedral arrangement. The NbO4^3− ion carries a −3 charge and forms salts with alkali and other cations, for example Na3NbO4 and K3NbO4.

The orthoniobate ion is isostructural with orthovanadate and is part of the family of oxoanions of group 5 elements. It serves as a basic building block in niobate chemistry and can participate in the formation of more complex polyoxometalate species under suitable conditions.

Formation and properties in solution and solids vary with pH. In basic aqueous solutions, NbO4^3− is stable, while acidification protonates the ion to give protonated species such as HNbO4^2− and H2NbO4^−, depending on the pH. In solid form, orthoniobates crystallize as salts with countercations, and their chemistry is linked to the wider niobium oxide material family.

Applications and significance are mainly within inorganic chemistry and materials science. Orthoniobate salts are encountered as precursors to niobium oxide materials and are studied within polyoxometalate chemistry for insights into oxoanion behavior, catalysis, and electrochemical properties. As a simple, well-defined NbO4^3− unit, it provides a convenient model for understanding niobium-centered oxide coordination.