Synthesis and single-crystal structures of fully dehydrated fully Sr2+-exchanged zeolite Y (FAU) and its benzene sorption complex, |Sr37.5|[Si117Al75O384]-FAU and |Sr37.5(C6H6)33(H2O)15|[Si117Al75O384]-FAU

Abstract

Single crystals of zeolite Y, |Na75|[Si117Al75O384]-FAU, were Sr2+ ion exchanged and fully dehydrated to generate |Sr37.5|[Si117Al75O384]-FAU (crystal 1) and next, benzene adsorbed to generate |Sr37.5(C6H6)33(H2O)15|[Si117Al75O384]-FAU (crystal 2, partially dehydrated). Crystal 1 was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO4)2 for 3 days followed by dehydration at 673 K and 1 × 10−6 Torr for 2 days. To prepare the benzene sorption complex (crystal 2), another dehydrated |Sr37.5|[Si117Al75O384]-FAU crystal was exposed to 50 Torr of benzene for 3 days at 294 K followed by evacuation for 30 min. at this temperature and 5 × 10−5 Torr. Their structures were determined crystallographically at 100(1) K using synchrotron X-radiation in the cubic space group Fd $$ \bar{3} $$ m. They were refined to the final error indices R 1/wR 2 = 0.051/0.125 and 0.057/0.154 using 598 and 590 reflections with F o > 4σ(F o) for crystals 1 and 2, respectively. In crystal 1, about 37.5 Sr2+ ions per unit cell are found at an unusually large number of crystallographically distinct positions, six. Eight Sr2+ ions per unit cell are at the centers of the double 6-rings (D6Rs, site I). Five additional Sr2+ ions are near site I. The site-I’ positions (in the sodalite cavities opposite D6Rs) are occupied by 2.5 Sr2+ ions per unit cell. Two Sr2+ ions are located at site II’ in the sodalite cavity. The remaining twenty Sr2+ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 9 and 11 ions per unit cell, respectively. Each of these Sr2+ ions coordinates to three framework oxygens. In this crystal, all sites are only sparsely occupied. In crystal 2, all Sr2+ ions are located at four crystallographic sites and 33 benzene molecules are found at two distinct sites within the supercages. One Sr2+ ion is at the center of the D6R. Fifteen Sr2+ ions are located at site I’. The remaining 21.5 Sr2+ ions are found at two nonequivalent sites II with occupancies of 19 and 2.5 ions per unit cell. Nineteen benzenes lie on threefold axes in the supercages, where they interact facially with the latter 19 site-II Sr2+ ions; occupancy = 19 molecules/32 sites. The remaining fourteen benzene molecules are found in 12-ring planes; occupancy = 14 molecules/16 sites. Each hydrogen of these 14 benzenes is ca. 2.9 A from six 12-ring oxygens.