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KMID : 1059519940380030186
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Journal of the Korean Chemical Society
1994 Volume.38 No. 3 p.186 ~ p.196
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Three Crystal Structures of Dehydrated Ag12-xNax-A (x = 4, 6, and 8) Treated with Rubidium Vapor
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Lee Hyun-Do
Kim Un-Sik
Park Jong-Yul
Kim Yang
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Abstract
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Three fully dehydrated partially Ag+-exchanged zeolite A(Ag4Na8-A, Ag6Na6-A, and Ag8Na4-A) were treated at 250℃ with 0.1 torr Rb vapor at 4 h. Their structures were determined by singlecrystal X-ray diffraction methods in the cubic space group Pm3m (a = 12.264(4) Å, a = 12.269(1) Å, and a= 12.332(3) Å, respectively) at 22(1)℃, and were refined to the final error indices, R(weighed), of 0.056 with 131 reflections, 0.068 with 108 reflections, and 0.070 with 94 reflections, respectively, for which I > 3σ(I). In these structures, Rb species are found at three different crystallographic sites; three Rb+ ions per unit cell are located at 8-ring centers, ca. 6.0∼6.8 Rb+ ions are found opposite 6-rings on threefold axes in the large cavity, and ca. 2.5 Rb+ ions are found on three fold axes in the sodalite unit. Also, Ag species are found at two different crystallographic sites; ca. 0.6∼1.0 Ag+ ion lies opposite 4-rings and about 1.8∼4.2 Ag atoms are located near the center of the large cavity. In these structures, the numbers of Ag atoms per unit cell are 1.8, 3.0, and 4.2, respectively, and these are likely to form hexasilver clusters at the centers of the large cavities. The Rb+ ions, by blocking 8-rings, may have prevented silver atoms from migrating out of the structure. Each hexasilver cluster is stabilized by coordination to 6-ring, 8-ring Rb+ ions, and also by coordination to a 4-ring Ag+ ion.
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