Encapsulation of Two Potassium Cations in Preyssler-Type Phosphotungstates: Preparation, Structural Characterization, Thermal Stability, Activity as an Acid Catalyst, and HAADF-STEM Images

Dipotassium cation
(K+)-encapsulated Preyssler-type phosphotungstate, [P5W30O110K2]13‑, was prepared by heating monobismuth (Bi3+)-encapsulated
Preyssler-type phosphotungstate, [P5W30O110Bi­(H2O)]12‑, in acetate buffer
in the presence of an excess amount of potassium cations. Characterization
of the isolated potassium salt, K13[P5W30O110K2] (1a), and its
acid form, H13[P5W30O110K2] (1b), by single crystal X-ray structure
analysis, 31P and 183W nuclear magnetic resonance
(NMR), Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry
(CV), high-resolution electrospray ionization mass spectroscopy (HR-ESI-MS),
and elemental analysis revealed that two potassium cations are encapsulated
in the Preyssler-type phosphotungstate molecule with formal D5h symmetry, which is the first
example of a Preyssler-type compound with two encapsulated cations.
Incorporation of two potassium cations enhances the thermal stability
of the potassium salt, and the acid form shows catalytic activity
for hydration of ethyl acetate. Packing of the Preyssler-type molecules
was observed by high-resolution high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM).