Single crystal structure of fully dehydrated fully K+-exchanged zeolite Y (FAU), K71Si121Al71O384

The crystal structure of K71-Y (FAU), K71Si121Al71O384 per unit cell, a = 24.9976(7) Å, dehydrated at 653 K and 8 × 10−6 Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3¯m at 294 K. The structure was refined using all intensities to the final error indices (using only the 695 reflections for which Fo > 4σ(Fo)) R1 = 0.045 (based on F) and R2 = 0.136 (based on F2). About 71 K+ ions per unit cell are found at an unusually large number of crystallographically distinct positions, eight. They exhibit the same degree of cation crowding seen in K92-X (FAU) as K+ ions continue to crowd into sites I and I′. Six K+ ions are at the centers of double 6-rings (D6Rs, site I; K–O = 2.733(5) Å and O–K–O (octahedral) = 89.90(14)° and 90.10(14)°). Five additional K+ ions are near site I (K–O = 2.530(11) and 2.972(15) Å); each is pushed off center by a K+ ion at a site-I′ position. Two site-I′ positions (in the sodalite cavities opposite D6Rs) are occupied by ten and five K+ ions, respectively, per unit cell; these K+ ions are recessed 1.30 Å and 1.68 Å into the sodalite cavities from their 3-oxygen planes (K–O = 2.581(15) and 2.69(3) Å, and O–K–O = 96.9(7)° and 84.9(14)°, respectively). These five site-I′ K+ ions push the five site-I K+ ions off center (K+ ⋯ K+ = 3.65(4) Å), and, in turn, are themselves pushed deeper into the sodalite cavities. Nearly filling site II in the supercages are 30.3(3) K+ ions, each of which extends 1.36 Å into the supercage from its 3-oxygen plane (K–O = 2.688(4) Å and O–K–O = 96.86(13)°). The 9.4(4) K+ ions at site III in the supercages each lie opposite the central ring of a triple 4-ring (K–O = 2.894(11) Å twice and O–K–O = 81.2(4)°). The remaining 2.0(7) and 1.5(6) K+ ions occupy two sites III′ near triple 4-rings in the supercage (K–O = 2.41(10), 2.89(5), 2.57(8), and 2.97(4) Å). K71-Y has 20 fewer K+ ions at III′ sites than K92-X; other much smaller occupancy differences are seen.