Dawson structure

The Dawson structure is a well-known structural motif for heteropoly acids.

The Dawson structure can be viewed as the fusion of two defect Keggin structure, fragments with three missing octahedra.

Unlike Keggin structures, there are two such anions, one at each side of the ellipsoidal anion.

[1] Commonly, Dawson structures feature phosphate as the central oxyanions.

When the Keggin anion [PW12O40]3− is allowed to stand in aqueous solution, it converts to [P2W18O62]6−.