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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 14, Number 5
BKCSDE 14(5)
May 20, 1993 

 
Title
Crystallographic Studies of Dehydrated Ag+ and K+ Exchanged Zeolite A Reacted with Alkali Metal Vapor
Author
Yang Kim*, Mi Suk Jeong, Karl Seff
Keywords
Abstract
The crystal structure of dehydrated Ag5.6K6.4-A, zeolite A ion-exchanged with K+ and Ag+ as indicated and dehydrated at 360℃, has been determined by single-crystal X-ray diffraction techniques. Also determined were the structures of the products of the reactions of this zeolite with 0.1 Torr of Cs vapor at 250℃ for 48 h and 72 h, and with 0.1 Torr of Rb vapor at 250℃ for 24 h. The structures were solved and refined in the cubic space group Pm3m at 21(l)℃ (a= 12.255(l) Å , 12.367(l) Å, 12.350(l) Å, and 12.263(l) Å, respectively). Dehydrated Ag5.6K6.4-A was refined to the final error indices R1= 0.044 and R2=0.037 with 202 reflections for which I>3σ(I). The crystal structures of the reaction products were refined to R1=0.087 and R2= 0.089 with 157 reflections, R1=0.080 and R2= 0.087 with 161 reflections, and R1= 0.071 and R2=0.061 with 88 reflections, respectively. In the structure of Ag5.6K6.4-A, K+ ions block all 8-oxygen rings, and one reduced Ag atom is found per sodalite cavity. Also, ca. 4.6 Ag+ ions and 3.4 K+ ions are found at 6-ring sites in the large cavity. The crystal structures of the reaction products show that all K+ and Ag+ ions have been reduced, and that all K+ atoms have left the zeolite. Cs or Rb species are found at three different crystallographic sites: 3.0 Cs+ or 3.0 Rb+ ions per unit cell occupy 8-ring centers, ca. 8.0 Cs+ ions or 5.7 Rb+ ions, are found on threefold axes opposite 6-rings deep in the large cavity, and ca. 2.5 Cs+ or 2.3 Rb+ ions are found on threefold axes in the sodalite unit. Also, 1 Rb+ ion lies opposite a 4-ring. Silver atoms, corresponding to 75% or 40% occupancy of hexasilver clusters stabilized by coordination to Cs+ or Rb+ ions, are found at the centers of the large cavities. In the crystal structures of dehydrated Ag5.6K6.4-A reacted with Cs vapor, excess Cs atoms are absorbed and these form (locally) cationic clusters such as (Cs4)3+ and (Cs6)4+.
Page
603 - 610
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