LEAD CLUSTERING IN A ZEOLITE-X

Single-crystal structure analyses of a Pb-exchanged zeolite X of ideal formula Pb-54(H3O)(12)(OH)(32)Al88S104O384 . nH(2)O (h-Pb-X), its deh ydrated form (d-Pb-X), and its partially Cs-exchanged form (h-(Pb,Cs)- X), of ideal formula Pb37Cs46(OH)(32)Al88Si104O384 . nH(2)O, are repor ted. The structures were refined in space group Fd3 (no. 203) to final R values of 0.077, 0.071, and 0.050, using 287, 253,and 426 independe nt reflections with I > 4 sigma (I). No significant change in the fram ework of the three structures was observed. The position and coordinat ion of the cation sites are discussed. Structural analysis of the thre e zeolites strongly supports the hypothesis that [Pb(OH)](4+)(4) clust ers fully occupy the sodalite cages in the hydrated forms, whereas upo n dehydration about one third of Pb2+ migrates from the sodalite cages into the large cavities.