Hydrated Cs+-Exchanged MFI Zeolites: Location and Population of Cs+ Cations and Water Molecules in Hydrated Cs6.6MFI from In and Ex Situ Powder X-ray Diffraction Data as a Function of Temperature and Other Experimental Conditions

Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97−106) to hydrated analogues, we have determined the crystal structures of members of the Cs6.6H0.3MFI·xH2O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs+ cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H2O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (∼1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H2O)n clusters and one (H2O)4 cluster in the MFI channel system:  Cs2(H2O)5 centered at x/y/z ∼ −0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H2O)4 ce...