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KMID : 1059519940380090621
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Journal of the Korean Chemical Society
1994 Volume.38 No. 9 p.621 ~ p.627
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Two Crystal Structures of Dehydrated Ag+- and Ca2+-Exchanged Zeolite A, Ag12-2xCax-A (x = 2 and 3) Treated with Cesium Vapor
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Song Seung-Hwan
Kim Yang
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Abstract
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Two crystal structures of dehydrated, Ag+ and Ca2+-exchanged zeolite A treated at 250℃ with 0.15 torr of Cs vapor have been determined by single-crystal X-ray diffraction technique in the cubic space group Pm3m at 21(1)℃ (a = 12.344(2) Å and 12.304(2) Å). Their structures were refined to the final error indices, R (weighted), of 0.091 with 180 reflections, and 0.093 with 179 reflections, respectively, for which I > 3σ(I). In each structure, Cs species are found at four different crystallographic sites: 3 Cs+ ions per unit cell are located at 8-ring centers, ca. 6.81∼7.14 Cs+ ions are found on opposite 6-rings on threefold axes in the large cavity, ca. 1.93∼2.03 Cs+ ions are found on threefold axes in the sodalite unit, and 0.53∼0.66 Cs+ ions lie on opposite 4-rings. Also, ca. 4.12∼4.27 Ag atoms are located near the center of the large cavity. In these structures, excess cesium atoms in a unit cell are associated with other Cs+ ions on a single threefold axis to form the linear cationic cluster (Cs4)3+. By blocking 8-rings, the Cs+ ions may have prevented silver atoms from migrating out of the structure. The Ag atoms are likely to have formed hexasilver clusters at the centers of the large cavities. Each hexasilver cluster is stabilized by coordination to 14 Cs+ ions.
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