Ammonium Octamolybdate, (NH₄)₂Mo₈O₂₅.16H₂O

Ammonium Octamolybdate, (NH₄)₂Mo₈O₂₅.16H₂O, has been described, but may be regarded as ammonium trihydrogen tetra-molybdate, NH₄O.(OH)₂MoO(O.MoO₂)₃.OH.5H₂O. This, if left in a vacuum over sulphuric acid, loses 5H₂O, and a further molecule of water when heated to 160° C. Its aqueous solution at 40° C. yields crystalline needles of the trihydrogen pentamolybdate NH₄O.(OH)₂MoO(O.MoO₂)₄.OH. Hexa-, hepta-, nona- undeca-, dodeca-, and trideca-molybdates have also been prepared.

The compound NH₃.MoO₂.(MoO₃)₂.5H₂O is described as an unstable brown crystalline substance obtained on mixing an aqueous solution of ordinary ammonium molybdate with a solution of molybdenum dioxide in hydrochloric acid.

The double salts NaNH₄Mo₃O₁₀.H₂O, 2Na₂O.7(NH₄)₂O.21MoO₃.15H₂O, and 3Na₂O.7(NH₄)₂O.25MoO₃.30H₂O have been described.

Three compounds have been described: NH₄IO₃.MoO₃.H₂O; (I₂O₅.2MoO₃)₄.3(NH₄)₂O.6H₂O; I₂O₅.2MoO₃.(NH₄)₂O.H₂O; as well as the periodo molybdates, (NH₄)₅IO₆.6MoO₃.6H₂O and (NH₄)HIO₆.4MoO₃.

Complex molybdates of ammonium, of the types (NH₄)₃H₆[R^•••(MoO₄)₆]7H₂O, where R^••• is Fe, Cr, or Al, and (NH₄)₃H₇[R^••(MoO₄)₆].xH₂O, where R^•• is Co, Mn, or Mg, have been prepared, as also have ammonium rare-earth-molybdates and a nicotine ammonium molybdate. The existence has been recorded of double salts of the following formulae: (NH₄)₂Cu(MoO₄)₂.2NH₃; CuMoO₄.2NH₃.H₂O; (NH₄)₂Cd(MoO₄)₂.2NH₃; (NH₄)₂Ni(MoO₄)₂.2NH₃; (NH₄)₂Co(MoO₄)₂. 2NH₃; and 3(NH₄)₂MoO₄.CO₂(MoO₄)₃.4MoO₃.10H₂O.