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. As in Keggin structures, the Dawson structure has an oxyanion at its core. Unlike Keggin structures, there are two such anions, one at each side of the ellipsoidal anion. An example is [S2W18O62], which can also be described as [(SO4)2(WO3)18].
Commonly, Dawson structures feature phosphate as the central oxyanions. When the Keggin anion [PW12O40] is allowed to stand in aqueous solution, it converts to [P2W18O62].
References
- Richardt, Peter J. S.; Gable, Robert W.; Bond, Alan M.; Wedd, Anthony G. (2001). "Synthesis and Redox Characterization of the Polyoxo Anion, γ*-: A Unique Fast Oxidation Pathway Determines the Characteristic Reversible Electrochemical Behavior of Polyoxometalate Anions in Acidic Media". Inorganic Chemistry. 40 (4): 703–709. doi:10.1021/ic000793q. PMID 11225112.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1016. ISBN 978-0-08-037941-8.