Fluoroxypermolybdates

When potassium fluoroxymolybdate MoO₂F₂.2KF.H₂O is dissolved in warm hydrogen-peroxide solution, oxidation occurs, and on cooling, fine yellow laminae, of composition MoO₃F₂.2KF.H₂O, separate. This salt reduces potassium permanganate in dilute sulphuric acid solution, with evolution of oxygen. Corresponding caesium and rubidium salts have also been obtained. A solution of ammonium paramolybdate in hydrofluoric acid, when treated with hydrogen peroxide in presence of excess ammonium fluoride, yields on evaporation the compound MoO₃F₂.3NH₄F, which may also be obtained by the direct action of hydrogen peroxide on the fluoroxymolybdate MoO₂F₂.3NH₄F. By the further action of hydrogen peroxide on the potassium salt, the compound MoO₄.2KF.H₂O may be obtained.