CRYSTAL-STRUCTURES OF FULLY DEHYDRATED CD(II)-EXCHANGED ZEOLITE-A ANDOF ITS CADMIUM SORPTION COMPLEX CONTAINING CD2-2(2+), AND CD-2(0)(, CD+, CD)

The crystal structures of Cd-6-A evacuated at 2 X 10(-6) Torr and 750 degrees C (a = 12.216(1) Angstrom) and of its cadmium sorption complex Cd-11-A (a = 12.127(1) Angstrom) have been determined by single-cryst al X-ray diffraction techniques in the cubic space group Pm ($) over b ar 3m at 21(1)degrees C. Their structures were refined to the final er ror indices, R(1) = 0.055 and R(W) = 0.067 with 191 reflections and R( 1) = 0.072 and R(W) = 0.064 with 197 reflections, respectively, for wh ich I > 3 sigma(I). In dehydrated Cd-6-A, six Cd2+ ions are found at t wo different 3-fold-axis sites near 6-oxygen-ring centers. Four Cd2+ i ons are each recessed 0.50 degrees into the sodalite cavity from the ( 111) plane of the three oxygens to which it is bound, and the other tw o extend 0.28 Angstrom into the large cavity from such planes. To prep are Cd-11-A, fully dehydrated Cd2+-exchanged zeolite A was exposed at 550 degrees C to 40 Torr of cadmium metal vapor and, during slow cooli ng, to lower pressures at lower temperatures. In this structure, three Cd2+ ions lie near 6-ring centers where each coordinates to three fra mework oxygens at 2.27(1) Angstrom, Six Cd+ ions are found at three cr ystallographic sites: three occupy 6-ring sites in the sodalite unit ( Cd-O = 2.68(1) Angstrom); two form (Cd-2)(2+) which associates with an 8-oxygen ring (Cd-Cd = 2.35(1) Angstrom, Cd-O = 2.50(2) Angstrom); an d one Cd+ ion lies at a 6-ring site in the large cavity (Cd-O 2.41(1) Angstrom). Two Cd atoms per unit cell are found deep in the large cavi ty far from the zeolite framework: they bond at a distance of 2.97(3) Angstrom. This dicadmium molecule is stabilized by interaction with a 6-ring Cd2+ ion and an 8-ring Cd-2(2+) ion. The sorption of cadmium me tal vapor into zeolite A has caused three of the six Cd-+(2) ions to b e reduced to Cd+. In addition, two cadmium atoms were sorbed per unit cell to form Cd2+.Cd-2(0).Cd-2(2+),a (Cd-5)(4+) cluster of low symmetr y in the large cavity.