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 Na92Si100Al92O384 p er unit cell, was determined by X-ray diffraction methods in the cubic spac e group Fd (3) over bar; a = 25.077(4) Angstrom at 21 degrees C. R-1 = 0.05 4 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. S ites I' and II are fully occupied with 32 Na+ ions each. The remaining 28 N a+ 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 dete rmination, and a consideration of the differing qualities of the diffractio n data are sufficient to reconcile all results. The substitution of four si licon atoms per unit cell into the aluminum equipoint necessarily has a com plicating effect. Considerations involving the ordering of these substitute d silicon atoms are not needed.