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KMID : 1059519890330050452
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Journal of the Korean Chemical Society
1989 Volume.33 No. 5 p.452 ~ p.458
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Two Crystal Structures of Dehydrated Calcium and Silver Exchanged Zeolite A, Ag12-2xCax-A (x = 2.5 및 5.0)
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Song Seong-Hwan
Park Jong-Yul
Kim Un-Sik
Kim Yang
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Abstract
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The crystal structures of vacuum-dehydrated Ag+ and Ca2+ exchanged zeolite A, Ag7Ca2.5-A(a = 12.310(1)Å) and Ag2Ca5-A(a = 12.287(2)Å) have been determined by single-crystal X-ray diffraction methods in the cubic space group Pm3m at 21(1)℃. The crystals of Ag7Ca2.5-A and Ag2Ca5-A were prepared by flow method using exchange solutions in which mole ratios of AgNO3 and Ca(NO3)2 were 1:50 and 1:1000, respectively, with total concentration of 0.05 M. Full-matrix least-squares refinement converged to the final error indices of R1 = 0.056 and R2 = 0.059 for Ag7Ca2.5-A, and R1 = 0.054 and R2 = 0.082 for Ag2Ca5-A using 306 and 348 reflections, respectively, for which I >3 σ (I). 5.5 Ag+ ions and 2.5 Ca2+ ions for Ag7Ca2.5-A and 2 Ag+ ions and 5 Ca2+ ions for Ag2Ca5-A lie on two crystallographically nonequivalent threefold axes on the 6-rings. Both structures indicate that smaller Ca2+ ions preferentially occupy 6-ring sites and larger Ag+ ions occupy 8-ring sites when total number of cations per unit cell is more than 8.
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