Disproportionation of an Element in a Zeolite. II. Crystal Structure of an Iodine Sorption Complex of Dehydrated Fully Cd2+-Exchanged Zeolite X Containing n-I5- as I-−I3+−I- and Square cyclo-I42+

The crystal structure of an iodine sorption complex of fully dehydrated, fully Cd 2+ -exchanged zeolite X, Cd 46 Si 100 Al 92 O 384 · 89.6I per unit cell ( a = 24.861(8) Å), has been determined by single-crystal X-ray diffraction methods in the cubic space group Fd 3̄ m at 21(1) °C. The crystal was prepared by ion exchange in a slightly basic aqueous stream 0.05 M in Cd 2+, followed by washing with distilled water at 80 °C. Dehydration was then done at 450 °C and 2 × 10 -6 Torr, followed by exposure in situ to zeolitically dry iodine vapor. The structure was refined to the final error indices R 1 = 0.044 and R 2 = 0.043 with 263 reflections, for which I > 3σ( I ). Forty-six Cd 2+ ions are found at four crystallographic sites: 14 at site I at the center of the hexagonal prism (Cd−O = 2.389(5) Å), 4 at site I‘ in the sodalite cavity just outside the hexagonal prism (Cd−O = 2.441(8) Å), 2.4 at site II‘ in the sodalite cavity (Cd−O = 2.200(9) Å), and the remaining 25.6 at site II near single six-oxygen rings in the supercage (Cd−O = 2.218(7) Å). All 44.8 diiodine molecules sorbed per unit cell have disproportionated to give 12.8 n -I 5 - anions with symmetry 2 and 6.4 square cyclo -I 4 2+ cations. The sorption reaction ends precisely when the eight supercages per unit cell are full (12.8/2 + 6.4/4 = 8.0). In cyclo -I 4 2+, I−I = 2.757(14) Å and 2.796(13) Å, and I−I−I = 90.0(5)°; each iodine atom is 3.167(10) Å from a framework oxygen (I−I···O = 159.4(4)°). In n -I 5 -, the central bond lengths are 2.473(14) Å and the terminal bond lengths are 2.534(13) Å, all less than 2.67 Å, the I−I distance in I 2 . The central bond angle, 114.8(7)°, is indicative of I 3 +, indicating that the terminal atoms are iodide ions. That the terminal atoms coordinate to Cd 2+ also indicates that they are iodide ions. The 12.8 n -I 5 - anions per unit cell each bridge between two site-II Cd 2+ ions in the supercage.