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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 7
BKCSDE 26(7)
July 20, 2005 

 
Title
Synthesis and Crystal Structure of Ag4Br4 Nanoclusters in the Sodalite Cavities of Fully K+-Exchanged Zeolite A (LTA)
Author
Woo Taik Lim*, Sik Young Choi, Bok Jo Kim, Chang Min Kim, In Su Lee, Seok Han Kim, Nam Ho Heo*
Keywords
Zeolite A, Ag4Br4 nanoclusters, Single-crystal X-ray diffraction, Crystal structure
Abstract
Ag4Br4 nanoclusters have been synthesized in about 75% of the sodalite cavities of fully K+-exchanged zeolite A (LTA). An additional KBr molecule is retained in each large cavity as part of a near square-planar K4Br3+ cation. A single crystal of Ag12-A, prepared by the dynamic ion-exchange of Na12-A with aqueous 0.05 M AgNO3 and washed with CH3OH, was placed in a stream of flowing 0.05 M KBr in CH3OH for two days. The crystal structure of the product K9(K4Br)Si12Al12O48·0.75Ag4Br4, a = 12.186(1) A) was determined at 294 K by single-crystal X-ray diffraction in the space group Pm m. It was refined with all measured reflections to the final error index R1 = 0.080 for the 99 reflections for which Fo > 4σ (Fo). The thirteen K+ ions per unit cell are found at three crystallographically distinct positions: eight K+ ions in the large cavity fill the six-ring site, three K+ ions fill the eight-rings, and two K+ ions are opposite four-rings in the large cavity. One bromide ion per unit cell lies opposite a four-ring in the large cavity, held there by two eight-ring and two six-ring K+ ions (K4Br3+). Three Ag+ and three Br- ions per unit cell are found on 3-fold axes in the sodalite unit, indicating the formation of nano-sized Ag4Br4 clusters (interpenetrating tetrahedra; symmetry Td; diameter ca. 7.9 A) in 75% of the sodalite units. Each cluster (Ag-Br = 2.93(3) A) is held in place by the coordination of its four Ag+ ions to the zeolite framework (each Ag+ cation is 2.52(3) A from three six-ring oxygens) and by the coordination of its four Br- ions to K+ ions through six-rings (Br-K = 3.00(4) A).
Page
1090 - 1096
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