Preparation of Preyssler-type Phosphotungstate with One Central Potassium Cation and Potassium Cation Migration into the Preyssler Molecule to form Di-Potassium-Encapsulated Derivative

A mono-potassium cation-encapsulated Preyssler-type phosphotungstate, [P 5 W 30 O 110 K] 14- ( 1 ), was prepared as a potassium salt, K 14 [P 5 W 30 O 110 K] ( 1a ), by heating mono-bismuth- or mono-calcium-encapsulated Preyssler-type phosphotungstates (K 12 [P 5 W 30 O 110 Bi(H 2 O)] or K 13 [P 5 W 30 O 110 Ca(H 2 O)]) in acetate buffer. Characterization of the potassium salt 1a by single-crystal X-ray structure analysis, 31 P and 183 W nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, high-resolution electrospray ionization mass spectroscopy, and elemental analysis revealed that one potassium cation is encapsulated in the central cavity of the Preyssler-type phosphotungstate molecule with a formal D 5 h symmetry. Density functional theory calculations have confirmed that the potassium cation prefers the central position of the cavity over a side position, in which no water molecules are coordinated to the encapsulated potassium cation. 31 P NMR and cyclic voltammetry analyses revealed the rapid protonation-deprotonation of the oxygens in the cavity compared to that of other Preyssler-type compounds. Heating of 1a in the solid state afforded a di-K + -encapsulated compound, K 13 [P 5 W 30 O 110 K 2 ] ( 2a ), indicating that a potassium counter-cation is introduced in one of the side cavities, concomitantly displacing the internal potassium ion from the center to a second side cavity, thus providing a new method to encapsulate an additional cation in Preyssler compounds.