Crystal Structures of Dehydrated Fully Mn²⁺-Exchanged Zeolite X and of Its Ethylene Sorption Complex

Abstract

The crystal structures of dehydrated Mn46Si100Al92O384 (a = 24.721(5) Å) and of its ethylene sorption complex Mn46Si100Al92O384·30C2H4 (a = 24.690(5) Å) have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3̄ at 21(1) °C. Each crystal was prepared by dehydration at 380 °C and 2 × 10-6 Torr for 2 days; the complex was then prepared by exposure to 300 Torr of ethylene gas at 24(1) °C, and its structure was determined in this atmosphere. Their structures were refined to the final error indices, R1 = 0.050 and R2 = 0.044 with 316 reflections and Rl = 0.064 and R2 = 0.061 with 313 reflections, respectively, for which I > 3σ(I). In each structure, 16 Mn2+ ions, each octahedrally coordinated by six oxygens of the zeolite framework, fill site I at the centers of the double six-rings. The remaining 30 Mn2+ ions in each structure are at site II in the supercage. Each site-II Mn2+ ion in the empty structure is three-coordinate and is quite close to the plane of the three oxygens to which it binds, projecting only 0.14 Å into the supercage. To coordinate laterally to an ethylene molecule, each moves 0.24 Å deeper into the supercage. These Mn2+ ions are 2.119(11) Å from three framework oxygens and 2.76(6) Å from each carbon atom of an ethylene molecule (CC = 1.10(8) Å). The long Mn2+−ethylene distance is indicative of physisorption.