Structure of a cyclopropane sorption complex of dehydrated fully Cd2+-exchanged zeolite A

The structure of a cyclopropane sorption complex of fully dehydrated Cd2+-exchanged zeolite A, Cd6Si12Al12O48. 4C(3)H(6) (a = 12.221(2) Angstrom), was determined by single-crystal X-ray diffraction techniques in the cubic space group Pm (3) over barm at 21 degreesC. Cd-6-A was dehydrated at 460 degreesC and 2 x 10(-6) Torr for two days, followed by exposure in situ to 100 Torr of zeolitically dry cyclopropane gas at 21(1)OC. The structure was determined in this atmosphere and refined to the final error indices R-1 = 0.050 and R-2 = 0.061 for the 178 reflections with I > 3 sigma (I). The six Cd2+ ions per unit cell all lie on threefold axes near six-ring centers, four in the large cavity and two in the sodalite cavity (Cd-O = 2.215(4)/2.256(2) Angstrom and O-Cd-O = 115.4(2)/112.3(2)degrees, respectively). Each of the four cyclopropane molecules per unit cell complexes facially to a large-cavity Cd2+ ion. The sorbed molecules lie on threefold axes of the zeolite, so the three carbon atoms of each cyclopropane molecule are equivalent and equidistant, 2.99(3) Angstrom, from their Cd2+ ion. The high thermal motions of the C3H6 molecules and their long distances to Cd2+ indicate that they are loosely held. The C-C bond length, 1.39(4) Angstrom, appears unreliably short due to this thermal motion. (C) 2000 Elsevier Science B.V. All rights reserved.