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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 23, Number 8
BKCSDE 23(8)
August 20, 2002 

Crystal Structures of Zeolite X Exchanged by Two Different Cations Structures of Cd32Cs28-X and Cd28Rb36-X (X = Si100Al92O384)
Gyoung Hwa Jeong, Yang Kim
Structure, Zeolite-X, Cadmium, Rubidium, Cesium
Two anhydrous crystal structures of fully dehydrated Cd2+ - and Cs+ -exchanged zeolite X, Cd32Cs28Si100Al92O384 (Cd32Cs28-X: a = 24.828(11) Å) and fully dehydrated Cd,sup>2+ - and Rb+ -exchanged zeolite X, Cd28Rb36Si100Al92O384 (Cd28Rb36-X: a = 24.794(2) Å), have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21(1)℃. The structures were refined to the final error indices, R1 = 0.058 and R2 = 0.065 with 637 reflections for Cd32Cs28-X and R1 = 0.086 and R2 = 0.113 with 521 reflections for Cd28Rb36-X for which I > 3σ(Ⅰ). In the structure of Cd,sub>32Cs28-X, 16 Cd2+ ions fill the octahedral sites I at the centers of the double six rings (Cd-O = 2.358(8)Å and O-Cd-O = 90.8(3)° ). The remaining 16 Cd2+ ions occupy site Ⅱ (Cd-O = 2.194(8)Å and O-Cd-O = 119.7(4)°) and six Cs+ ions occupy site Ⅱ opposite to the single six-rings in the supercage; each is 2.322Å from the plane of three oxygens (Cs-O = 3.193(13) and O-Cs-O = 73.0(2)°). Aboutten Cs+ ions are found at site Ⅱ', 1.974Å into the sodalite cavity from their three oxygen plane (Cs-O = 2.947(8)Å and O-Cs-O = 80.2(3)°). The remaining 12 Cs+ ions are distributed over site Ⅲ' (Cs-O = 3.143(9) and O-Cs-O= 59.1(2)°). In the structure of Cd28Rb36-X, 16 Cd2+ ions fill the octahedral sites I at the center of the double-sixrings (Cd-O = 2.349(15) and O-Cd-O = 91.3(5)° ). Another 12 Cd2+ ions occupy two different II sites (Cd-O = 2.171(18)/2.269(17)Å and O-Cd-O = 119.7(7)/113.2(7)°). Fifteen Rb+ ions occupy site Ⅱ (Rb-O = 2.707(17)Å and O-Rb-O = 87.8(5)°). The remaining 21 Rb+ ions are distributed over site Ⅲ' (Rb-O = 3.001(16)Å and O-Rb-O = 60.7(4)°). It appears that the smaller and more highly charged Cd2+ ions prefer sites I and Ⅱ in that order, and the larger Rb+ and Cs+ ions, which are less able to balance the anionic charge of the zeolite framework, occupy sites Ⅱ and Ⅱ' with the remainder going to the least suitable site in the structure, site Ⅲ'.The maximum Cs+ and Rb+ ion exchanges were 30% and 39%, respectively. Because these cations are too largeto enter the small cavities and their charge distributions may be unfavorable, cation-sieve effects might appear.
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