Aqueous Crystallization of Manganese(II) Group 6 Metal Oxides

Aqueous salt metathesis reactions of manganese(II) salts and various chromate, molybdate, and tungstate salts afford a series of manganese group 6 metal oxides. The chromate reactions form a previously unknown phase, KMn₂(CrO₄)₂(OH)(H₂O) (1), whereas the tungstate reactions afford a simpler, hydrated phase, MnWO₄·H₂O (4). In these reactions, the countercation appears to influence the crystal form and size of the products. The molybdate reactions display countercation-dependent phase selectivity. Sodium and ammonium molybdates afford hydrated manganese molybdenum oxide, MnMoO₄·H₂O (3), whereas potassium molybdate affords the new molydenum analogue of the chromate phase, KMn₂(MoO₄)₂(OH)(H₂O) (2). Counteranion effects are more subtle, with crystal form and size representing the primary differences between the products from reactions using sulfate, acetate, or chloride salts of manganese(II). Each phase undergoes thermal dehydration, affording α-MnMoO₄ from 3 and MnWO₄ (hübnerite) from 4.