Aluminium Molybdates

Simple molybdates of aluminium (Aluminium Molybdates) have not been prepared, but by dissolving aluminium hydroxide in solutions of alkali tri- or para-molybdates, and allowing to crystallise, salts of the type 3R^•₂O.Al₂O₃.12MoO₃.aq. are obtained. These may be represented as derivatives of the alkali aluminates thus: R^•₃Al(Mo₂O₇)₃.aq. The following have been described:

3(NH₄)₂O.Al₂O₃. 12MoO₃.19H₂O (or 20 or 22H₂O), white, lustrous, quadratic crystals.

3K₂O.Al₂O₃.12MoO₃.20H₂O, flat white plates or cubes, stable in air.

3Na₂O.Al₂O₃.12MoO₃.22H₂O, efflorescent needles.

The barium salt, 4BaO.Al₂O₃.12MoO₃.14H₂O, is precipitated when a soluble barium salt is added to a solution of the potassium compound. The complex, Al₂O₃.12MoO₃, is very stable, and similar compounds with analogous complexes, containing the sesquioxides of chromium, cobalt, iron, manganese, and nickel, have also been prepared.