Crystal Structures of Encapsulates within Zeolites. 3. Xenon in Zeolite A

The positions of Xe atoms encapsulated in the cavities of fully dehydrated zeolite A of unit-cell composition Cs3Na8HSi12Al12O48 (Cs3-A) have been determined. Cs3-A was exposed to 255 atm of xenon at 400 °C for 7 days, followed by cooling at pressure to encapsulate Xe atoms; a second crystal was treated similarly at 450 atm, and a third at 1020 atm. The resulting crystal structures of Cs3-A(2.5Xe) (crystal 1, a = 12.245(2) A, R1 = 0.056, R2 = 0.059), Cs3-A(4.5Xe) (crystal 2, a = 12.258(2) A, R1 = 0.061, R2 = 0.058), and Cs3-A(5.25Xe) (crystal 3, a = 12.236(2) A, R1 = 0.061, R2 = 0.057) were determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 21(1) °C and 1 atm. The approximately 2.5, 4.5, and 5.25 Xe atoms per unit cell, respectively, are distributed over three crystallographically distinct positions. At the center of each sodalite unit in crystals 1, 2, and 3, respectively, are 0.5, 0.75, and 0.75 Xe atoms at Xe(1); in addition, off center in crystal 3 are 0.25 Xe a...