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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 2
BKCSDE 21(2)
February 20, 2000 

 
Title
Two Crystal Structures of Dehydrated Zn2+-Exchanged Zeolite X: Zn46Si100Al92O384 ·8ZnO and Zn13Tl66Si100Al92O384 · 2ZnO
Author
Seok Hee Lee, Yang Kim
Keywords
Abstract
The crystal structures of fully dehydrated fully Zn 2+ -exchanged zeolite X, Zn46Si100Al92O384 ·8ZnO(Zn46-X ·8ZnO; a = 24.710(4)Å), and that of fully dehydrated Zn 2+ -and Tl+ -exchanged zeolite X, Zn13Tl66Si100Al92O384 ·2ZnO(Zn13Tl66-X ·2ZnO; a = 24.984(4)Å), have been determined by single-crystal X-ray diffraction methods in the cubic space group Fd3 at 21(1)℃. Zn46-X ·8ZnO was prepared by ion exchange in a flowing stream of 0.05 M aqueous Zn(NO3)2 for 2 days. Zn13Tl66-X ·2ZnO was similarly prepared using a solution of 0.025 M each in Zn(NO3)2 and TlNO3. Each crystal was then dehydrated at 400 ℃ and 2 x 10-6 Torr for 2 days. Their structures were refined to the final error indices R1 = 0.052 and R2 = 0.047, with 292 reflections for Zn46-X ·8ZnO, and R1 = 0.039 and R2 = 0.034, with 382 reflections for Zn13Tl66-X ·2ZnO; I > 3 σ(I). In the structure of dehydrated Zn46-X ·8ZnO, Zn 2+ ions are located at four different crystallographic sites. Two Zn 2+ ions lie at the center of a double six-ring (site I, Zn-O = 2.584(10)Å, O-Zn-O = 103.2(4)。). Twenty-eight Zn 2+ ions are located at site I' displaced from a shared hexagonal face into a sodalite cavity (Zn-O = 1.984(12)Å, O-Zn-O = 108.0(4)。). Eight over-exchanged Zn 2+ ions, which lie at site II', are recessed ca. 0.61Å into the sodalite cavity from their three O(2) oxygen plane (Zn-O = 2.109(11)Å and O-Zn-O = 109.1(4)。 ), and each associates with three framework oxygens and also with one nonframework oxygen deeper in the sodalite unit in a distorted tetrahedral arrangement. The remaining sixteen Zn 2+ ions are found at site II in a supercage (Zn-O = 1.986(10)Å and O-Zn-O = 119.7(5)。). In the structure of a dehydrated Zn13Tl66-X·2 ZnO, thirteen Zn 2+ ions are found at site I' adjacent to D6R (Zn-O = 2.036(14)Å and O-Zn-O = 119.8(5)°). Two over-exchanged Zn 2+ ions, which lie at site II', are recessed ca. 0.66 A into the sodalite cavity from their three O(2) oxygen plane (Zn-O = 2.276(36)Å and O-Zn-O = 109.9(5)°). Tl + ions are located at four different crystallographic sites. Nineteen Tl + ions lie at site I' in the sodalite cavity (Tl-O = 2.536(13)Å and O-Tl-O = 88.0(4)°). Thirty Tl + ions occupy site II, recessed 1.68Å into a supercage from the three O(2) oxygen plane (Tl-O = 2.678(10)Å and O-Tl-O = 88.0(4)°). Four-teen Tl + ions are found at site III deep in the supercage (Tl-O = 2.835(14)Å, O-Tl-O = 75.4(4)°). The remaining three Tl + ions are found at site III' in a supercage (Tl-O = 3.007(62)Å, Tl-O = 2.408(59)Å, O-Tl-O = 55.4(13)°).
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