Reinvestigation of the Crystal Structure of Dehydrated Sodium Zeolite X

The structure of a single crystal of dehydrated zeolite Na−X selected from a batch grown by Petranovskii in Russia, of composition Na 92 Si 100 Al 92 O 384 per unit cell, was determined by X-ray diffraction methods in the cubic space group Fd 3̄; a = 25.077(4) Å at 21 °C. R 1 = 0.054 for the 320 reflections for which F o > 4σ( F o ); wR 2 based on F 2 and all data is 0.140. Na + ions are found at four crystallographic sites. Sites I‘ and II are fully occupied with 32 Na + ions each. The remaining 28 Na + ions partially occupy two 12-ring (site III‘) positions with 10(4) near an O−Al−O sequence and 18(4) near an O−Si−O sequence. These results differ from those of the two previous investigations of dehydrated Na−X, which, in turn, disagree substantially with each other. The near energy equivalence of two (or more) III‘ sites, the presence of an impurity cation in one determination, and a consideration of the differing qualities of the diffraction data are sufficient to reconcile all results. The substitution of four silicon atoms per unit cell into the aluminum equipoint necessarily has a complicating effect. Considerations involving the ordering of these substituted silicon atoms are not needed.