Sodium polytungstate

Sodium polytungstate (SPT) is a compound which has been successfully used in the manufacture of heavy liquids for a relatively short period.

Solid SPT are white crystals and aqueous SPT is a light yellow-green transparent solution. In powder form, SPT is a 12-fold aggregated isopolytungstate with a molar mass of 2986.12 g/Mol. The structure of polytungstate is modelled using octahedra in which the oxygen atoms are located at the corners and the tungsten atoms at the center of the octahedra. When represented as a spherical model, the oxygen atoms form a dense spherical shell while the tungsten atoms fill the open spaces in the octahedra. Because of this structure this substance may be considered a true metatungstate, represented structurally as Na₆[H₂W₁₂O₄₀]. In true metatungstates, both of the protons are located in the central empty space of the polyanion and are unable to penetrate the external shell of the spherical casing.