Synthesis of Preyssler-Type Phosphotungstate with Sodium Cation in the Central Cavity through Migration of the Ion

Thermal migration of sodium cation in the cavity of Preyssler-type phosphotungstate is reported here. Heating of a Preyssler-type compound, [P5W30O110Na(side)(H2O)](14), in which a sodium cation occupies one of the two side cavities, at 300 degrees C forms a new compound, [P5W30O110 Na(center)](1)(4-), in which the sodium cation is encapsulated in the central cavity. Characterization by single crystal X-ray structure analysis, NMR spectroscopy, elemental analysis, IR, and ESI-MS confirmed the structure of the compound. The thermal displacement ellipsoid of the central sodium, estimated by the crystallographic study, is elongated along the direction perpendicular to the equatorial plane of the Preyssler molecule. These results confirmed prediction using DFT calculation by Lopez and Poblet (ref. 21, J. Am. Chem. Soc. 2007, 129, 12244.) that the most stable site for sodium is the central cavity with a slight shift from the center of the molecule.