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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 27, Number 5
BKCSDE 27(5)
May 20, 2006 

 
Title
Synthesis and Crystal Structure of Lead Iodide in the Sodalite Cavities of Zeolite A (LTA)
Author
Seok Han Kim, Woo Taik Lim*, Ghyung Hwa Kim, Heung Soo Lee, Nam Ho Heo*
Keywords
Zeolite A, Lead iodide, Single-crystal X-ray diffraction, Crystal structure
Abstract
The positions of PbI2 molecule synthesized into the molecular-dimensioned cavities of |K6(Pb4I2)(PbI2)0.67- (H2O)2|[Si12Al12O48]-LTA have been determined. A single crystal of |Pb6|[Si12Al12O48]-LTA, prepared by the dynamic ion-exchange of |Na12|[Si12Al12O48]-LTA with aqueous 0.05 M Pb(NO3)2 and washed with deionized water, was placed in a stream of flowing aqueous 0.05 M KI at 294 K for three days. The resulting crystal structure of the product (|K6(Pb4I2)(PbI2)0.67(H2O)2|[Si12Al12O48]-LTA, a = 12.353(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 = 0.062 for 623 reflections which Fo > 4σ(Fo). 4.67 Pb2+ and six K+ ions per unit cell are found at three crystallographically distinct positions: 3.67 Pb2+ and three K+ ions on the 3-fold axes opposite six-rings in the large cavity, three K+ ions off the plane of the eight-rings, and the remaining one Pb2+ ion lies opposite four-ring in the large cavity. 0.67 Pb2+ ions and 1.34 I- ions per unit cell are found in the sodalite units, indicating the formation of a PbI2 molecule in 67% of the sodalite units. Each PbI2 (Pb-I = 3.392(7) A) is held in place by the coordination of its one Pb2+ ion to the zeolite framework (a Pb2+ cation is 0.74 A from a six-ring oxygens) and by the coordination of its two I- ions to K+ ions through six-rings (I-K = 3.63(4) A). Two additional I- ions per unit cell are found opposite a four-ring in the large cavity and form Pb2K2I5+ and PbK2I3+ moieties, respectively, and two water molecules per unit cell are also found on the 3-fold axes in the large cavity.
Page
679 - 686
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