XM12O40n

XM12O40n denotes a family of heteropolyanions in polyoxometalate chemistry, typically written as [XM12O40]n−. In this formulation, X is a heteroatom (for example P, Si, Ge, B or As) occupying the central site, and M denotes twelve addenda atoms, most commonly tungsten (W) or molybdenum (Mo). The overall negative charge n depends on the oxidation state of the metal centers and the identity of X, with common members including [PW12O40]3−, [SiW12O40]4−, [PMo12O40]3−, and [GeMo12O40]4−.

The ion adopts the Keggin structure, consisting of a central XO4 tetrahedron surrounded by a shell of twelve MO6 octahedra, all interconnected through shared oxide ligands to form a highly symmetric 40-oxygen framework. The M12 core is common across the family, while substitution at X or M yields a wide range of derivatives with adjustable redox and acidity properties.

Typical preparation involves acidification of aqueous solutions containing the appropriate heteroatom source and addenda metal precursors, followed by crystallization or salt formation. The resulting ions are generally stable in acidic media and can be isolated as various counter-cations or as crystalline hydrates. They are soluble in water and polar solvents, and their chemistry is well-characterized in inorganic polyoxometalate literature.

Applications_and significance include catalytic oxidation and acid-catalyzed transformations, electrochemical redox applications as electron-transfer mediators, and roles as versatile building blocks in materials science. Their tunable composition and robust, well-defined structures continue to make XM12O40n derivatives a focal point in catalysis, energy storage, and supramolecular assembly research.