ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 43, Number 4
JKCSEZ 43(4)
August 20, 1999 

Two anhydrous clystal structures of fully dehydrated, Ca2+- and Tl+-exchanged zeolite X,Ca18Tl56Si100Al92O384(Ca18Tl56-X;α=24.883(4) Å) and Ca32Tl28Si100Al92O384(Ca32Tl28-X;α=24.973(4) Å) per unit cell, have been determined by single-crystal X-ray diffaction techniques in the cubic space group Fd3 at21(1)℃ Ca18Tl56-X was prepared by ion exchange in a flowing stream of O.O45 M aqueous Ca(NO3)2 and 0.005 M TlNO3 Ca32Tl28-X was prepared similarly using a mixed solution of O.0495 M Ca(NO3)2 and O.0005M TlNO3 Each crystal was then dehydrated at 360 ℃ and 2 × 10-6 Torr for 2 days Their structures were refined to the final error indices, R1=O.O39 and R2=O.O36 with 382 reflections for Ca18Tl56-X , and R1=O.O46 and R2=0.045 with 472 reflection for Ca32Tl28-X for which />3σ(I). In the structures of dehydrated Ca18Tl56-X and Ca32Tl28-X, Ca2+ and Tl+ ions are located at six crystallographic sites Sixteen Ca2+ ions fill the octahedral sites I at the centers of double six rings (Ca18Tl56-X Ca-O=2.42(1) and O-Ca-O=93.O6(4)˚; Ca32Tl28-X Ca-O=2.40(1) Å and O-Ca-O=93.08(3)˚). In the structure of Ca18Tl56-X, another two Ca2+ ions occupy site II (Ca-O=2.35(2) Å and O-Ca-O=111.69(2)˚) and twenty six Tl+ ions occupy site II opposite single six-rings in the supercage; each is 1.493 Å from the plane of three oxygens (Tl-O=2.70(8)Å and O-Tl-O=92.33(4)˚) About four T+ ions are found at site II',1.695 Å into sodalite cavity from their three oxygen plane (Tl-O=2.81 (1) and O-Tl-O=87.48(3)). The remaining twenty six Tl+ ions are distributed over site III'(Tl-O=2.82 (1) Å and Tl-O=2.88(3)˚) In the structure of Ca32Tl28-X, sixteen Ca2+ ions and fifteen Tl+ ions occupy site III' (Ca-O=2.26(1) Å and O-Ca-O=119.14(4)˚; Tl-O=2.70(1) Å and O-Tl-O=92.38˚) and one Tl+ ion occupies site II The remaining twelve Tl+ ions are distributed over site III'. It appears that Ca2+ ions prefer sites I and II in that order and Tl+ ions occupy the remaining sites