Molybdic Metaphosphate

Molybdic Metaphosphate has been prepared by the reduction, at red heat, of a solution of molybdenum trioxide in metaphosphoric acid, either by hydrogen or by molybdenum disulphide in a current of carbon dioxide. It is also obtained by heating molybdenum disulphide or the dioxide with orthophosphoric acid in a current of carbon dioxide. It is a yellow crystalline powder, of composition Mo₂O₃.3P₂O₅ or Mo(PO₃)₃, stable in dry air, and of density at 0° C. = 3.28. On heating, it is only oxidised superficially; heated with water in a sealed tube, it is decomposed at 250° to 300° C., forming orthophosphoric acid. Hot concentrated mineral acids have no action upon it, but it dissolves slowly in warm aqua regia, and it is readily attacked by hot caustic alkali. It forms double phosphates when fused with alkali phosphates.

Other simple phosphates of trivalent molybdenum have not been prepared, but the complex salt, sodium molybdenipyrophosphate, Na(MoP₂O₇).12H₂O, has been obtained as a brown crystalline precipitate by adding tripotassium molybdenum hexachloride, K₃MoCl₆, to a solution of sodium pyrophosphate at 80° to 90° C.