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

Abstract

The positions of Xe atoms encapsulated in the cavities of fully dehydrated zeolite A of unit-cell composition Cs 3 Na 8 HSi 12 Al 12 O 48 (Cs 3 -A) have been determined. Cs 3 -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 Cs 3 -A(2.5Xe) (crystal 1, a ) 12.245(2) Å, R 1 ) 0.056, R 2 ) 0.059), Cs 3 -A(4.5Xe) (crystal 2, a ) 12.258(2) Å, R 1 ) 0.061, R 2 ) 0.058), and Cs 3 -A(5.25Xe) (crystal 3, a ) 12.236(2) Å, R 1 ) 0.061, R 2 ) 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 atoms at Xe(4), opposite a six-ring in the sodalite unit. Opposite four-rings in the large cavity at Xe(2) are 1, 2, and 2.25 Xe atoms, respectively, for the three crystals. Opposite six-rings in the large cavity at Xe(3) are 1, 1.75, and 2 Xe atoms, respectively. Relatively strong interactions of Xe(3) atoms with six-ring Na + ions are observed: Na-Xe(3) ) 3.18(2), 3.22(2), and 3.38(2) Å, respectively. In Cs 3 -A(2.5Xe), two Xe atoms are found in each large cavity: Xe 2 with a 4.54(4) Å distance may exist. Cs 3 -A(4.5Xe) may be viewed as a mixture of two kinds of unit cells: in most of their large cavities, four Xe atoms form a rhombus with Xe(2)-Xe(3) ) 4.51(3) Å and Xe(2)-Xe(3)-Xe(2) ) 95.1(5)°. Cs 3 -A(5.25Xe) may also be viewed as having two kinds of large cavities: 75% contain a rhombus of four Xe atoms, Xe(2)-Xe(3) ) 4.45(2) Å and Xe(2)-Xe(3)-Xe(2) ) 97.3(4)°. The remaining 25% have five Xe atoms arranged trigonal-bipyramidally with three Xe(2)'s equatorial and two Xe(3)'s axial (Xe(2)-Xe(3) ) 4.45(2) Å). These arrangements of encapsulated Xe atoms in the large cavity are stabilized by alternating dipoles induced on Xe(2) and Xe(3) atoms by four-ring oxygens and six-ring Na + ions, respectively.

EPR and DFT Study on the Stabilization of Radiation-Generated Methyl Radicals in Dehydrated Na-A Zeolite

“…There is no direct evidence that methane molecules could gain access to the β cavities. However, in a crystallographic study of zeolite A containing Xe, which is about the same size as methane molecules, a Xe molecule was always found in the center of sodalite β, indicating that passage of Xe atoms through the hexagonal window is due to dynamic processes at higher temperature. , …”

“…However, in a crystallographic study of zeolite A containing Xe, which is about the same size as methane molecules, a Xe molecule was always found in the center of sodalite β, indicating that passage of Xe atoms through the hexagonal window is due to dynamic processes at higher temperature. 48,49 The EPR spectra of γ-irradiated Na-A/CH 4 zeolite do not depend much on the pressure of adsorbed methane. The EPR parameters and temperature transformation of EPR signals are almost identical for methane pressures in the range 0.4-13 kPa except for the line width, which increases from 0.3 mT for 0.4 kPa of CH 4 to 0.58 mT for 13 kPa.…”

Disproportionation of an Element in a Zeolite. I. Crystal Structure of a Sulfur Sorption Complex of Dehydrated, Fully Cd2+-Exchanged Zeolite X. Synthesis of Tetrahedral S44+ and n-S42+, Two New Polyatomic Cations of Sulfur

“…59 Zn 7 -HAlO 4 10+ 60 is similarly hosted by a sodalite cavity, but it has lower symmetry. Larger cations that fill and extend out of sodalite cavities are Cs 4 3+ , 16,24,25 Pb 7 O(OH) 3 9+ , 61 (Pb 2+ , Pb 4+ ) 4 -Pb 4 2+ O 4 ca. 12+ , 62,63 and the tetrahedral cation (Cd 2+ Zn) 8 16+ .…”

“…Well-defined clusters have been found in A, X, and Y type zeolites. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] By choosing different zeolites, nanoclusters with different structures and electronic properties can be built from the same sorbate. Attempts have been made to synthesize nanoclusters of semiconductors such as CdS, PbS, and PbI 2 inside zeolites.…”

Doing Chemistry in a One-Nanometer Test Tube (In a Zeolite)

“…The same is true when complexes prepared by sorption at high pressures (loading) are returned to ambient pressures, unless the windows are blocked. [15] My work has generally proceeded as follows: select a single zeolite crystal, perform ion exchange if desired to introduce a cation of interest, and then, all without exposure to the atmosphere, dehydrate the crystal by increasing its temperature slowly under dynamic vacuum, do the chemistry one step at a time in situ within the vacuum system, seal off the capillary containing the crystal with a small flame, and determine the structure of that crystal. ''Do the chemistry'' has usually meant exposure to a gas or vapor, e.g., Zn(g), Cs(g), S(g), Xe, H 2 , NO, D 2 O, C 3 H 6 , or C 6 H 6 , at a temperature and pressure to be selected.…”