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

The crystal structure of K-71-Y (FAU), K-71 Si-121 AL(71)O(384) per unit cell, a = 24.9976(7) angstrom, dehydrated at 653 K and 8 x 10(-6) Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Mint at 294 K. The structure was refined using all intensities to the final error indices (using only the 695 reflections for which F-o > sigma(4F(o))) R-1 = 0.045 (based on F) and R-2 = 0.136 (based on F-2). 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 K-92-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) angstrom and O-K-O (octahedral) = 89.90(14)degrees and 90.10(14)degrees). Five additional K+ ions are near site I (K-O = 2.530(11) and 2.972(15) angstrom); 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 angstrom and 1.68 angstrom into the sodalite cavities from their 3-oxygen planes (K-O = 2.581(15) and 2.69(3) angstrom, and O-K-O = 96.9(7)degrees and 84.9(14)degrees, respectively). These five site-I' K+ ions push the five site-I K+ ions off center (K+ center dot center dot center dot K+ = 3.65(4) angstrom), 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 angstrom into the supercage from its 3-oxygen plane (K-O = 2.688(4) angstrom and O-K-O = 96.86(13)degrees). 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) angstrom twice and O-K-O = 81.2(4)degrees). 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) angstrom). K-71-Y has 20 fewer K+ ions at III' sites than K92-X; other much smaller occupancy differences are seen. (c) 2006 Elsevier Inc. All rights reserved.