Tungstate

Tungstate commonly denotes the tungsten oxoanion $\mathrm{W}{\mathrm{O}}_4^{2-}$ and salts containing it. The formula specifies one tungsten and four oxygen atoms with a net charge of $-2$. The Protein Data Bank chemical-component dictionary identifies its WO4 ligand as tungstate(VI), while the corresponding PubChem record gives the dianion formula.^[ref]

Taking each oxygen to have oxidation state $-2$, charge balance gives $x+4(-2)=-2$, hence $x=+6$ for tungsten. Oxidation state and net ionic charge therefore answer different questions. A neutral salt needs two singly charged cations per tungstate anion, or one doubly charged cation. That count balances charge without requiring the ions to form a discrete isolated molecule in a crystal.

Tungstate also provides an experimental structural probe. In a 1995 study of Escherichia coli fumarase C, a competitive tungstate derivative helped locate an active site containing contributions from three protein subunits.^[ref] Binding a detectable inorganic ion can reveal where a molecular interaction occurs. It does not by itself show that the ion is the enzyme's physiological substrate or that every binding site catalyzes a reaction.