Crystal Structure of a Benzene Sorption Complex of Dehydrated Fully Ca²⁺-Exchanged Zeolite X

Abstract

The crystal structure of a benzene sorption complex of fully dehydrated Ca2+-exchanged zeolite X, Ca46Si100Al92O384·28C6H6 (a = 24.953(6) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3̄ at 21 °C. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous Ca(NO3)2 for 3 days, followed by dehydration at 400 °C and 2 × 10-6 Torr for 2 days, followed by exposure to about 48 Torr of benzene vapor at 16 °C. The structure was determined in this atmosphere and refined to the final error indices R 1 = 0.051 and R w = 0.049 with 358 reflections for which I > 3σ(I). Filling site I (at the centers of the double six-rings), 16 octahedrally coordinated Ca2+ ions (Ca−O = 2.399(7) Å) are found per unit cell. The remaining 30 Ca2+ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 8 and 22 ions. Each of these Ca2+ ions coordinates to three framework oxygens, either at 2.270(10) or 2.318(7) Å, respectively, and extends either 0.24 or 0.55 Å, respectively, into the supercage from the plane of the three oxygens to which it is bound. The benzene molecules are found at two distinct sites within the supercages. Twenty-two benzenes lie on 3-fold axes in the large cavities, where they interact facially with the latter 22 site-II Ca2+ ions (Ca2+−benzene center = 2.75 Å; occupancy = 22 molecules/32 sites). The remaining six benzene molecules are found in 12-ring planes; occupancy = 6 molecules/16 sites. Each hydrogen of these six benzenes is ca. 3.0 Å from three 12-ring oxygens.

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

“…This hypothesis was validated by the results of FTIR and Raman spectroscopies on xylene adsorption in FAUs that clearly showed the formation of a π‐complex between the xylene aromatic system and the alkali cations as well as additional CH⋅⋅⋅O contacts with the basic lattice . Whereas toluene and xylenes can only form π‐complexes with individual cations or form stacked aggregates at higher loadings, benzene becomes symmetrically aligned in the 12‐membered ring window of the supercage as a result of the formation of multiple van der Waals interactions between benzene C−H groups and the framework oxygens ,. Similarly, the specific alignment of ferrocene in NaY pores has been attributed to the concert effect of multiple weak van der Waals interactions between the cyclopentadienyl ligands and pore walls .…”

Two distinguishable lithium sites in the zeolite Li-ZSM-5 as revealed by adsorption of CO: an infrared spectroscopic and thermodynamic characterisation

“…Bolis et al 19 found similar phenomena in the adsorption of CO on Ca-supporting aluminas, and a slight movement of extraframework cations upon adsorption of gases in zeolites was suggested several times in the literature. In particular, single crystal X-ray diffraction work has shown 22 that the Ca 2+ ion in calciumexchanged zeolite X moves by about 25 pm (away from the zeolite framework) upon adsorption of benzene. To our knowledge, however, this is the first report on cation movement upon gas adsorption in zeolites based on IR spectroscopy and microcalorimetric measurements.…”

Synthesis and Single-crystal Structure of Fully Dehydrated Fully Ca2+exchanged Zeolite Y (FAU), |Ca35.5|[Si121Al71O384]-FAU

“…In the single-crystal structures of Ca46-X․28C6H6, 7 Ca46-X․ 8C9H12, 10 and Ca46-X․16CH3NH2, 11 the coordination of benzene, mesitylene, and methylamine caused Ca 2+ ion to move 0.24, 0.26, and 0.15 Å, respectively, along its 3-fold axis more deeply into the supercage from the three O(2) plane, compared to its position in dehydrated |Ca 46 Table 3). This is attributed 4 with Al and Si alternating at the tetrahedral sites.…”

“…Using single-crystal X-ray diffraction technique in the cubic space group Fd 3 at 24 (1) o C, Seff et al 3,4 determined the structure of fully dehydrated, fully Ca 2+ -exchanged zeolite X (Si/Al = 1.09) to learn the cation positions and the site selectivity. They also studied the crystal structures of ethylene, 5 acetylene, 5 hydrogen sulfide, 6 benzene, 7 ammonia, 8 cyclopropane, 9 mesitylene, 10 and methylamine 11 complexes of fully dehydrated fully Ca 2+ -exchanged zeolite X (Si/Al = 1.09) to observe the geometry and chemistry of sorption in zeolites (i.e., to determine shifts in cation and framework atomic positions, to observe cationsorbate interactions, and to detect resultant changes in sorbed molecule geometry). They noted that there were some unusual two kinds of site-II Ca 2+ ions in benzene, 7 mesitylene, 10 and methylamine 11 sorption complexes of Ca…”