Stable polyoxometalate insertion within the mesoporous metal organic framework MIL-100(Fe)Electronic supplementary information (ESI) available: Elemental analysis, schematic representations of the structure, X-ray thermodiffraction patterns, X-ray diffraction patterns of Na2HPMo12/MIL-100(Fe)noF and nitrogen isotherms and porous distribution of Na2HPMo12/MIL-100(Fe)noF. See DOI: 10.1039/c0jm02381g

Successful encapsulation of polyoxometalate (POM) within the framework of a mesoporous iron trimesate MIL-100(Fe) sample has been achieved by direct hydrothermal synthesis in the absence of fluorine. XRPD, 31 P MAS NMR, IR, EELS, TEM and 57 Fe Mössbauer spectrometry corroborate the insertion of POM within the cavities of the MOF. The experimental Mo/Fe ratio is 0.95, in agreement with the maximum theoretical amount of POM loaded within the pores of MIL-100(Fe), based on steric hindrance considerations. The POM-MIL-100(Fe) sample exhibits a pore volume of 0.373 cm 3 g −1 and a BET surface area close to 1000 m 2 g −1 , indicating that small gas molecules can easily diffuse inside the cavities despite the presence of heavy phosphomolybdates. These latter contribute to the decrease in the overall surface area, due to the increase in molar weight, by 65%. Moreover, the resulting Keggin containing MIL-100(Fe) solid is stable in aqueous solution with no POM leaching even after more than 2 months. In addition, no exchange of the Keggin anions by tetrabutylammonium perchlorate in organic media has been observed. Keggin 12-phosphomolybdates were encapsulated into mesoporous iron trimesate MIL-100(Fe) by direct synthesis, maintaining gas accessibility and avoiding POM leaching.