CADMIUM(I) AND DICADMIUM(I) - CRYSTAL-STRUCTURES OF CADMIUM(II)-EXCHANGED ZEOLITE-A EVACUATED AT 500-DEGREES-C AND OF ITS CADMIUM SORPTION COMPLEX

The crystal structures of partially dehydrated, fully Cd2+-exchanged zeolite A, [Cd(H20)2+]3(Cd2+)3-A (a = I 2.242 (2) Å), and of its cadmium metal sorption complex, [Cd(H20)2+]3(Cd+)3(Cd2 2+)1, 5-A (a = 12.291 (1) Å), have been determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m. The structures were refined to final R (weighted) indices of 0.039 and 0.062, respectively. All six Cd2+ ions in the unit cell of [Cd(H20)2+]3(Cd2+)3-A are associated with 6-oxygen rings of the aluminosilicate framework. Three of these Cd2+ ions extend somewhat into the large cavity where each is three coordinate (Cd(II)-O ca. 2.17 Å) to three framework oxides. The other three Cd2+ ions are recessed into the sodalite unit where each is coordinated to three framework oxides and a fourth oxide (probably OH- of a dissociated H2O molecule) in a near-tetrahedral manner. Upon exposure to cadmium metal vapor the three three-coordinate Cd2+ ions react to form Cd+ and Cd2 2+ species. The three four-coordinate ions move to the planes of 6-oxygen rings where each remains coordinated to three framework oxides and to one nonframework oxide; the latter, however, has moved to the large cavity. Three Cd+ ions are found on threefold axes, each coordinated to three oxides of the zeolite framework (Cd(I)-O ca. 2.33 Å). Two of these are in the sodalite unit, and the other extends into the large cavity. One Cd2 2+ ion is located in the sodalite unit and is coordinated to the framework at one end only. The remaining 1/2Cd2 2+ ion per unit cell is symmetrically coordinated across an 8-oxygen ring in the large cavity. The Cd-Cd distance in Cd2 2+ is the same (2.35 Å) for the two modes of coordination. The existence of the univalent state of cadmium has been noted before in studies of cadmium metal dissolved in molten cadmium halides and in irradiated aqueous solutions of Cd2+. © 1979, American Chemical Society. All rights reserved.