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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 28, Number 2
BKCSDE 28(2)
February 20, 2007

Title	Crystal Structure of Fully Dehydrated Partially Cs⁺-Exchanged Zeolite X, Cs₅₂Na₄₀-X (The Highest Cs⁺-Exchanged Level Achieved by Conventional Method and Confirmation of Special Site Selectivity)
Author	Myung Nam Bae
Keywords	Zeolite X, Cesium, Sodium, Double six-rings, Six-rings
Abstract	The crystal structure of fully dehydrated partially Cs⁺-exchanged zeolite X, [Cs₅₂Na₄₀Si₁₀₀Al₉₂O₃₈₄], a = 24.9765(10) A, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21 °C. The crystal was prepared by flow method for 5 days using exchange solution in which mole ratio of CsOH and CsNO₃ was 1 : 1 with total concentration of 0.05 M. The crystal was then dehydrated at 400 °C and 2 × 10^-6 Torr for 2 days. The structure was refined to the final error indices, R₁ = 0.051 and wR₂ (based on F²) = 0.094 with 247 reflections for which F_o > 4σ (F_o). In this structure, about fifty-two Cs⁺ ions per unit cell are located at six different crystallographic sites with special selectivity; about one Cs⁺ ion is located at site I, at the centers of double oxygen-rings (D6Rs), two Cs⁺ ions are located at site I', and six Cs⁺ ions are found at site II'. This is contrary to common view that Cs⁺ ions cannot pass sodalite cavities nor D6Rs because six-ring entrances are too small. Ring-opening by the formation of ?OH groups and ring-flexing make Cs⁺ ions at sites I, I', and II' enter six-oxygen rings. The defects of zeolite frameworks also give enough mobility to Cs+ ions to enter sodalite cavities and D6Rs. Another six Cs⁺ ions are found at site II, thirty-six are located at site III, and one is located at site III' in the supercage, respectively. Forty Na⁺ ions per unit cell are located at two different crystallographic sites; about fourteen are located at site I, the centers of D6Rs and twenty-six are also located at site II in the supercage. Cs⁺ ions and Na⁺ ions at site II are recessed ca. 0.34(1) A and 1.91(1) A into the supercage, respectively. In this work, the highest exchange level of Cs⁺ ions per unit cell was achieved in zeolite X by conventional aqueous solution methods and it was also shown that Cs⁺ ion could pass through the sixoxygen rings.
Page	251 - 256
Full Text	PDF / Supporting Information

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