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 (3) over bar; a = 25.077(4) Angstrom at 21 degrees C. R(1) = 0.054 for the 320 reflections for which F(o) > 4 sigma(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.