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Crystal Structure of Dehydrated Partially Ag$^+$-Exchanged Zeolite A treated with Cesium Vapor at 250${^{circ}C}$
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  • Crystal Structure of Dehydrated Partially Ag$^+$-Exchanged Zeolite A treated with Cesium Vapor at 250${^{circ}C}$
저자명
Kim. Duk-Soo,Song. Seong-Hwan,Kim. Yang
간행물명
Bulletin of the Korean Chemical Society
권/호정보
1989년|10권 3호|pp.234-238 (5 pages)
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이 논문은 한국과학기술정보연구원과 논문 연계를 통해 무료로 제공되는 원문입니다.
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기타언어초록

The crystal structure of partially $Ag^+$-exchanged zeolite A, $Ag_{3.2}Na_{8.8}$-A, vacuum dehydrated at $360^{circ}C$ and then exposed to 0.1 torr of cesium vapor for 12 hours at $250^{circ}C$ has been determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m (a = 12.262(2)${AA});at;21(1)^{circ}C$. The structure was refined to the final error indexes $R_1=0.068;and;R_2=0.072$ by using 338 reflections for which $I_o;>;3{sigma}(I_o)$ and the composition of unit cell is $Ag_{3.2}Cs_{8.8}-A.;3;Cs^+$ ions lie on the centers of the 8-rings at sites of D4h symmetry. Two crystallographycally different 6-ring $Cs^+$ ions were found: 1.5 $Cs^+$ ions at Cs(2) are located inside of sodalite cavity and 4.3 $Cs^+$ ions at Cs(3) are located in the large cavity. The fractional occupancies observed at Cs(2) and Cs(3) indicate that the existence of at least three types of unit cells with regard to the 6-ring $Cs^+$ ions. For example, 50% of unit cells may have two $Cs^+$ ions at Cs(2) and 4 $Cs^+$ ions at Cs(3). 30% of unit cells may have one Cs+ ion at Cs(2) and 5 $Cs^+$ ions at Cs(3). The remaining 20% would have one $Cs^+$ ion at Cs(2) and 4 $Cs^+$ ions at Cs(3). On threefold axes of the unit cell two non-equivalent Ag atom positions are found in the large cavity, each containing 0.64 and 1.92 Ag atoms, respectively. A crystallographic analysis may be interpreted to indicate that 0.64 $(Ag_5)^+$ clusters are present in each large cavity. This cluster may be viewed as a tetrasilver molecule $(Ag_4)^0$(bond length, 2.84${AA}$) stabilized by the coordination of one $Ag^+$ ion.