Solid-State Ion Migration in the Preyssler-Type Phosphotungstate for the Preparation of the Dipotassium Cation-Encapsulated Derivative

The heat-driven solid-state transformations of K salts of the Na-encapsulated Preyssler-type phosphotungstates, K₁₄P₅W₃₀O₁₁₀Na(side)(H₂O)] and K₁₄P₅W₃₀O₁₁₀Na(center)], are reported herein. K₁₄P₅W₃₀O₁₁₀Na(side)(H₂O)] contains one Na⁺ in one of the side cavities and a coordinating H₂O molecule while K₁₄P₅W₃₀O₁₁₀Na(center)] contains one Na⁺ in the central cavity. The heating of K₁₄P₅W₃₀O₁₁₀Na(side)(H₂O)] produces P₅W₃₀O₁₁₀Na(center)]^14–, P₅W₃₀O₁₁₀K(center)]^14–, and P₅W₃₀O₁₁₀K(side)₂]^13–. P₅W₃₀O₁₁₀K(center)]^14– and P₅W₃₀O₁₁₀K(side)₂]^13– contain mono-K⁺ in the central cavity and di-K⁺ in both side cavities, respectively. The heating of potassium salt of P₅W₃₀O₁₁₀Na(center)]^14– produces P₅W₃₀O₁₁₀K(center)]^14– and P₅W₃₀O₁₁₀K(side)₂]^13–. These results indicate that heating, at 200–500 °C, causes the migrations of Na⁺ and K⁺, without the collapse of the molecule. K₁₄P₅W₃₀O₁₁₀Na(side)(H₂O)] was successfully converted to K₁₂NaP₅W₃₀O₁₁₀K(side)₂] by repeated solid-state heating, which was periodically interrupted by dissolution, in H₂O, and drying.