Single crystal structure of fully dehydrated, excessively Cd2+-exchanged zeolite Y, ∣Cd27.5(Cd8O4)2∣[Si121Al71O384]-FAU, containing Cd8O48+ clusters

The structure of fully dehydrated, excessively Cd2+-exchanged zeolite Y, ∣Cd27.5(Cd8O4)2∣[Si121Al71O384]-FAU, has been determined using single-crystal X-ray diffraction techniques in the cubic space group Fd3¯m at 21(1) °C. Ion exchange was accomplished by allowing an aqueous stream 0.05 M in Cd2+, pH 7, to flow past the crystal for 5 days. The crystal was then dehydrated at 350 °C and 2 × 10−6 Torr for 2 days. The structure was determined in vacuum and was refined using all 690 unique reflections to the final error indices (based only upon the 357 reflections for which Fo > 4σ(Fo)), R1 = 0.060 and wR2 = 0.151. In this structure, Cd2+ ions occupy five crystallographic sites. Eight Cd2+ ions half fill site I at the centers of the double six-rings (Cd–O (octahedral) = 2.498(11) Å), eight Cd2+ ions one-quarter fill a site-I′ position deep in the sodalite cavities (Cd–O (octahedral) = 2.559(17) Å) and another eight one-quarter fill a more conventional site-I′ position (Cd–O = 2.278(14) Å), eight Cd2+ ions one-quarter fill site II′ inside the sodalite cavities (Cd–O = 2.192(11) Å), and the remaining 11.5 Cd2+ ions are found at site II in the supercages (Cd–O = 2.179(9) Å). The Cd2+ ions at the first I′ position form, with non-framework oxide ions, Cd4O4 clusters (interpenetrating tetrahedra, symmetry 4¯3m(Td), Cd–O = 2.33(4) Å) in two of the eight sodalite cavities per unit cell. Each Cd4O4 unit coordinates further via its oxygen atoms to four more Cd2+ ions at site II′, Cd–O = 1.86(11) Å, to give the larger cationic Cd8O48+ clusters (symmetry still 4¯3m(Td)). During ion exchange at pH 7, zeolite Y had apparently imbibed eight Cd(OH)2 molecules per unit cell; these decomposed upon vacuum dehydration to give, with eight additional Cd2+ ions, two Cd8O48+ clusters.