Something about Ammonium Paratungstate Structure from Lanthanum Tungsten Electrode Material

Ammonium paratungstate (APT) is one of the materials for the preparation of lanthanum tungsten electrode, which is a kind of white crystalline salt. After World War II, there are literatures showing that the anion in (NH₄)₁₀(W₁₂O₄₁) ·5H₂O has been proved to be [H₂W₁₂O₄₂]¹⁰⁻, holding two hydrogen atoms inside the cage. Tungsten-oxygen cage, the focus of the anion, requires 42 oxygen molecules. Therefore, the correct formula expression for ammonium paratungstate is (NH₄)₁₀[H₂W₁₂O₄₂] ·4H₂O. On the contrary to the paratungstate A ion, whose anion is [W₇O₂₄]⁶⁻, the paratungstate B ion is [H₂W₁₂O₄₂]¹⁰⁻ ion, which is similar to the paramolybdate ion. However, the existence of the paratungstate A ion can’t be confirmed by NMR (Nuclear Magnetic Resonance) spectroscopy.

Before 1930, there had been some argument about the exact composition of the salt, and someone had proposed the two structures at that time: (NH₄)₁₀W₁₂O₄₁ and (NH₄)₆W₇O₂₄. And O.W. Gibbs had said that” the alkali tungstate are unusually complex. Salts of essentially different formula is so close in composition ratio that the differences lie very near the unavoidable errors of analysis. The analysis is hardly sufficiently close to deciding the question on purely analytical grounds." 

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