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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 13, Number 1
BKCSDE 13(1)
January 20, 1992 

Two Crystal Structures of Ethylene and Acetylene Sorption Complexes of Dehydrated Fully Ca2+-Exchanged Zeolite A
Se Bok Jang, Sung Doo Moon, Jong Yul Park, Un Sik Kim, Yang Kim*
Two crystal structures of ethylene (a= 12.272(2) Å) and acetylene (a = 12.245(2) Å) sorption complexes of dehydrated fully Ca2+-exchanged zeolite A have been determined by single crystal X-ray diffraction techniques in the cubic space group, Pm3m at 21(l)℃. Their complexes were prepared by dehydration at 360℃ and 2×10-6 Torr for 2 days, followed by exposure to 200 Torr of ethylene gas and 120 Torr of acetylene gas both at 24℃, respectively. The structures were refined to final R (weighted) indices of 0.062 with 209 reflections and 0.098 with 171 reflections, respectively, for which I > 3σ(I). The structures indicate that all six Ca2+ ions in the unit cell are associated with 6-oxygen ring of the aluminosilicate framework. Four of these extend somewhat into the large cavity where each is coordinated to three framework oxide ions and an ethylene molecule and/or an acetylene molecule. The carbon to carbon distance in ethylene sorption structure is 1.48(7) Å and that in acetylene sorption structure 1.25(8) Å. The distances between Ca2+ ion and carbon atom are 2.87(5) Å in ethylene sorption structure and 2.95(7) Å in acetylene sorption structure. These bonds are relatively weak and probably formed by the electrostatic attractions between the bivalent Ca2+ ions and the polarizable π-electron density of the ethylene and/or acetylene molecule.
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