Structure of a cyclopropane sorption complex of dehydrated fully Cd 2+-exchanged zeolite A

Abstract

The structure of a cyclopropane sorption complex of fully dehydrated Cd 2+-exchanged zeolite A, Cd 6Si 12Al 12O 48·4C 3H 6 ( a=12.221(2) Å), was determined by single-crystal X-ray diffraction techniques in the cubic space group Pm 3 ̄ m at 21°C. Cd 6–A was dehydrated at 460°C and 2×10 −6 Torr for two days, followed by exposure in situ to 100 Torr of zeolitically dry cyclopropane gas at 21(1)°C. 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 σ( I). The six Cd 2+ 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) Å and O–Cd–O=115.4(2)/112.3(2)°, respectively). Each of the four cyclopropane molecules per unit cell complexes facially to a large-cavity Cd 2+ 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) Å, from their Cd 2+ ion. The high thermal motions of the C 3H 6 molecules and their long distances to Cd 2+ indicate that they are loosely held. The C–C bond length, 1.39(4) Å, appears unreliably short due to this thermal motion.