NH46Mo7O244H2O

NH46Mo7O244H2O is the chemical formula for ammonium heptamolybdate tetrahydrate, an ammonium salt of the heptamolybdate anion Mo7O24^6− with four waters of crystallization. In common notation this compound is written as (NH4)6Mo7O24·4H2O.

Composition and structure: The solid comprises six ammonium cations (NH4+) balancing a single heptamolybdate anion (Mo7O24^6−) and four water molecules of hydration. This composition gives a yellow to pale yellow crystalline solid that dissolves readily in water.

Physical properties: Ammonium heptamolybdate tetrahydrate appears as yellow crystals or a pale yellow solid. It is readily soluble in water, forming solutions that are used as sources of molybdenum in further chemical synthesis. Upon heating, the tetrahydrate loses its water of crystallization and, at higher temperatures, decomposes to molybdenum oxide while releasing volatile components such as ammonium-containing species.

Preparation: It is prepared by treating molybdate salts with ammonium sources in aqueous solution and then crystallizing the tetrahydrate by evaporation or cooling. The compound is distributed commercially as a reagent for laboratory and industrial use due to its role as a convenient Mo source.

Applications: In analytical chemistry, ammonium heptamolybdate is used as a reagent in phosphate determination, often forming a phosphomolybdate complex that is subsequently reduced in colorimetric assays. In materials science and catalysis, it serves as a practical precursor for molybdenum oxide catalysts and for the synthesis of Mo-containing oxides. It also functions as a starting material for preparing other ammonium molybdate salts.

Safety: Ammonium molybdate compounds are of moderate toxicity and should be handled with appropriate safety precautions to avoid ingestion, inhalation, or skin contact. Store and dispose of them according to applicable regulations.