Ammonium Paratungstate Structure

In more recent literature (post WWII period), the anion in (NH₄)₁₀(W₁₂O₄₁)·5H₂O has been shown to be [H₂W₁₂O₄₂]¹⁰⁻, containing two hydrogen atoms, keeping two hydrogen atoms inside the cage. The tungsten-oxygen cage, that is the heart of the anion requires 42 oxygen molecules. The correct formula notation for ammonium paratungstate is therefore (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O. The [H₂W₁₂O₄₂]¹⁰⁻ ion is known as the paratungstate B ion, as opposed to the paratungstate A ion, that has the formula [W₇O₂₄]⁶⁻, similar to the paramolybdate ion. The existence of the paratungstate A ion, could not be confirmed by NMR spectroscopy, however.

Before about 1930, there has been some dispute about the exact composition of the salt, and both (NH₄)₁₀W₁₂O₄₁ and (NH₄)₆W₇O₂₄ were proposed. O.W. Gibbs remarked about this:

"The alkali tungstates are numerous and unusually complex. Salts of essentially different formul;ae approach so closely in percentage composition, that the differences lie very near the unavoidable errors of analyses. The analyses are hardly sufficiently close to decide the question upon purely analytical grounds."

You may visit our website www.tungsten-powder.com to get more information.