Abstract: The slightly soluble crystals K₁₀Na₂H₂P₂W₁₆O₆₀· 18H₂O can be obtained by additionally adding excess KCl to a slightly acidic solution (pH6.5～6.9) which can be prepared by acidizing the mixture of para Aand Na₂HPO₄ with HCl to the right pHvalue.Para Ais freshly prepared by acidizng the solution of Na₂WO₄ with HCl to the [H⁺]/[WO₄^2-] value of 1.14.The compound was characterized by elemental analysis, VO²⁺ titration, UV, ³¹PNMR and ¹⁸³W NMR spectroscopy.The structure of the compound belongs to Dawson type of species.This compound decomposes as a heteropoly anion H₇PW₈O₃₃^6- when it dissolves in water by heating and also decomposes as a main product PW₁₁O₃₉^7- when the counterion in solution is changed from K⁺ to Na⁺.

Key words: Divacant Dawson structure, Phosphotungstate, ¹⁸³W NMR