Preparation and Characterization of Preyssler‐type Phosphotungstic Acid, H 15– n [P 5 W 30 O 110 M n + ], with Different Encapsulated Cations ( M = Na, Ca, Bi, Eu, Y, or Ce), and their Thermal Stability and Acid Catalyst Properties

Preyssler‐type phosphotungstic acid, H 15– n [P 5 W 30 O 110 M n + ], with different encapsulated cations ( M = Ca 2+ , Bi 3+ , Eu 3+ , Y 3+ , Ce 3+ ) were prepared and characterized using 31 P NMR and IR spectroscopy, acid‐base titration, and elemental analyses. The p K a value of an internal proton of Ca‐encapsulated derivative, [P 5 W 30 O 110 CaH in ] 12– , was estimated to be 5.9. Their thermal stabilities and acid catalyst properties were compared with a parent Na‐encapsulated Preyssler‐type phoshotungstic acid, H 14 [P 5 W 30 O 110 Na]. Thermal stability of the Preyssler‐type molecule was increased by exchanging the encapsulated Na + with Bi 3+ , Eu 3+ , or Ce 3+ , with keeping their high acidic properties.