Crystal Structure of Dehydrated <TEX>$Rb^{+}$</TEX>-Exchanged Zeolite X, <TEX>$Rb_{71}Na_{21}Si_{100}Al_{92}O_{384}$</TEX>

The crystal structure of dehydrated <TEX>$Rb^+$</TEX>-exchanged zeolite X, stoichiometry <TEX>$Rb_{71}Na_{21}-X; (Rb_{71}Na_{21}Si_{100}Al_{92}O_{384})$</TEX> per unit cell, has been determined from single-crystal X-ray diffraction date gathered by counter methods. The structure was solved and refined in the cubic space group Fd3, a=25.007(3) Å at 21(1) ℃. The crystal was prepared by ion exchange in a flowing stream using a 0.05 M aqueous RbOH solution (pH=12.7). The crystal was then dehydrated at 360 ℃ and <TEX>$2{ imes}10^{-6}$</TEX> torr for two days. The structure was refined to the final error indices, <TEX>$R_1=0.047$</TEX> and <TEX>$R_2=0.040$</TEX> with 239 reflections for which I> 3σ(I). In this structure, 71 <TEX>$Rb^+$</TEX> ions per unit cell are found at six different crystallographic sites and 21 <TEX>$Na^+$</TEX> ions per unit cell are found at two different crystallographic sites. Four and a half <TEX>$Rb^+$</TEX> ions are located at site Ⅰ, the center of the hexagonal prism. Nine <TEX>$Rb^+$</TEX> ions are found at site Ⅰ' in the sodalite cavity (Rb-O=2.910(15) Å and O-Rb-O=78.1(4)°). Eighteen <TEX>$Rb^+$</TEX> ions are found at site Ⅱ in the supercage (Rb-O=2.789(9) Å and O-Rb-O=92.1(4)°). Two and a half <TEX>$Rb^+$</TEX> ions, which lie at site Ⅱ', are recessed ca. 2.07 Å into the sodalite cavity from their three O(2) oxygen planes (Rb-O=3.105(37) Å and O-Rb-O=80.6(5)°). Thirty-two <TEX>$Rb^+$</TEX> ions are found at site Ⅲ deep in the supercage (Rb-O=2.918(12) Å and O-Rb-O=71.9(4)°), and five <TEX>$Rb^+$</TEX> ions are found at site Ⅲ'. Seven <TEX>$Na^+$</TEX> ions also lie at site Ⅰ. Fourteen <TEX>$Na^+$</TEX> ions are found at site Ⅱ in the supercage (Na-O=2.350(19) Å and O-Na-O=117.5(6)°).