Crystal structure of an ethylene sorption complex of fully dehydrated, fully oxidized, fully Ag+-exchanged zeolite X

The crystal structure of an ethylene sorption complex of fully dehydrated, fully oxidized, fully Ag+-exchanged zeolite X, (Ag+)(92)Si100Al92O384.27C(2)H(4)(a = 24.981(9) Angstrom), [Ag-92(C2H4)(27)][Al92Si100O384]-FAU, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd (3) over bar at 21 degreesC. Ion exchange was accomplished by allowing 0.05 M aqueous AgNO3 to flow past a crystal for 3 days to give hydrated Ag92Si100Al92O384. This crystal was dehydrated at 400 degreesC for 2 days followed by cooling to 21 degreesC, both in a flowing stream of zeolitically dry oxygen gas (790 Torr), followed by evacuation at 2 x 10(-6) Torr for 20 min. To prepare the ethylene sorption complex, this colorless crystal was treated at 21 degreesC with 300 Torr of zeolitically dry ethylene gas for 2 h. The structure of the resulting dark yellow crystal was determined in this atmosphere and was refined to the final error index wR(2) based on F-2 and all data (1155) of 0.293; R-1 = 0.069 for the 221 reflections for which F-0 > 4sigma (F-0). In this structure, per unit cell, 12 Ag+ ions were found at the octahedral site I (Ag-O = 2.63(2) Angstrom) and 16 Ag+ ions occupy the nearby site-I' positions (Ag-O = 2.47(3) Angstrom). A significant 2.951-Angstrom interaction must occur between the Ag+ ions at sites I and I'; linear (Ag-3)(3+) is proposed. Thirty-two Ag+ ions fill the single 6-rings, 27 at site II (Ag-O = 2.41(2) Angstrom) and 5 at site II' (Ag-O = 2.30(4) Angstrom). Each of the 27 site-II Ag+ ions extends 1.08 Angstrom into the supercage to form a strong lateral pi-complex with an ethylene molecule. In turn, each C2H4 molecule forms two electrostatic hydrogen bonds to framework oxygens. The remaining 32 Ag+ ions occupy four different III' sites. The Ag+ site occupancies changed substantially upon the sorption of ethylene. (C) 2003 Elsevier Inc. All rights reserved.