Heteropoly Compounds

complex compounds whose anion is formed by two different acid-forming oxides. The classic examples of heteropoly compounds are molybdenum phosphoric acid H₃PO₄·12MoO3·nH₂O and tungsten iodic acid HIO₃·6W0₃·H₂O. (The formulas shown here express the empirical composition of the heteropoly compounds.)

The structures of many heteropoly compounds have not been definitively established, but for most of them the structure is expressed by two-coordination formulas of the type H₃[PMo₁₂O₄₀] (molybdenum phosphoric acid) and H₇[IW₆O₂₄] (tungsten iodic acid). The majority of heteropoly compounds are soluble in water, from which they crystallize in the form of hydrates with numerous water molecules. Heteropoly compounds are used in analytical chemistry for determining rubidium, cesium, phosphorus, vanadium, arsenic, and germanium; in biochemistry they are used to precipitate dissolved protein; they are also used as catalysts.