Two Crystal Structures of the Vacuum-Dehydrated Fully $Ag^+$-Exchanged Zeolite X

Two crystal structures of the vacuum dehydrated -exchanged zeolite X have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21(1) (a=24.922(1) and a=24.901(1), respectively). Each crystal was ion exchanged in flowing streams of aqueous for three days. The first crystal was dehydrated at 300 and torr for two days. The second crystal was similarly dehydrated at 350. Their structures were refined to the final error indices, with 227 reflections, and with 334 reflections, respectively, for which I > 3(I). In the first crystal, Ag species are found at five different crystallographic sites: sixteen ions fill the site I, the center of the double 6-ring, thirty-two Ag0 atoms fill the I' site in the sodalite cavities opposite double six-rings, seventeen ions lie at the 32-fold site II' inside the sodalite cavity at the single six-oxygen ring in the supercage, fifteen Ag+ ions lie at the 32-fold site II, in the supercage, and the remaining twelve ions lie at site III' in the supercage at a little off two-fold axes. In the second crystal, all Ag species are located similarly as crystal 1; 16 at site I, 28 at site I', 16 at site II, 16 at site II', 6 at site III and 6 at site III'. Total 88 silver species were found per unit cell. The remaining four Ag atoms were migrated out of the zeolite framework to form small silver crystallites on the surface of the zeolite single crystal. In the first structure, the numbers of Ag atoms per unit cell are approximately 32.0 and these may form tetrahedral clusters at the centers of the sodalite cavities. The probable four-atom cluster is stabilized by coordination to two ions. The Ag-Ag distance in the cluster, ca. 3.05 , is a little longer than 2.89 , Ag-Ag distance in silver metal. At least two six-ring ions on sodalite cavity (site II') must necessarily approach this cluster and this cluster may be viewed as a distorted octahedral silver cluster, (Ag6)2+.