Crystal structures of fully dehydrated fully Sr2+-exchanged zeolite X and of its ammonia sorption complex

The crystal structures of fully dehydrated Sr-46-X [Sr46Si100Al92O384; a=25.214(7) Angstrom] and of its ammonia sorption complex, Sr-46-X . 102NH(3) [Sr46Si100Al92O384. 102NH(3); a=25.127(7) Angstrom], have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21(1)degrees C. The Sr-46-X crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO4)(2) for 5 days followed by dehydration at 360 degrees C and 2 x 10(-6) Torr for 2 days. To prepare the ammonia sorption complex, another dehydrated Sr-46-X crystal was exposed to 230 Torr of zeolitically dried ammonia gas for 1 h followed by evacuation for 12 h at 21(1)degrees C and 5 x 10(-4) Torr. The structures were refined to the final error indices, R-1=0.043 and R-w=0.039 with 466 reflections, and R-1=0.049 and R-w=0.044 with 382 reflections, for which I>3 sigma(I). In dehydrated Sr-46-X, all Sr2+ ions are located at two crystallographic sites. 16 Sr2+ ions are at the centers of the double six-rings, filling that site (site I, Sr-O = 2.592(6) Angstrom). The remaining 30 Sr2+ ions are in the supercage (site II); each extends 0.56 Angstrom into the supercage from the plane of its three nearest oxygen atoms (Sr-O=2.469(6) Angstrom). In the structure of Sr-46-X . 102NH(3), the Sr2+ ions are located at three crystallographic sites: 12 are found at site I [Sr-O = 2.652(10) 0 Angstrom]; four in the sodalite units (site I') each coordinated to three framework oxygen atoms at 2.654(9) A and also to three ammonia molecules at 2.76(8) Angstrom. The remaining 30 Sr2+ ions lie at site II. Each extends 1.12 Angstrom into the supercage where it coordinates to three framework oxygen atoms at 2.584(7) Angstrom and also to three ammonia molecules at 2.774(24) Angstrom. (C) 1999 Elsevier Science B.V. All rights reserved.