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

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-crystal X-ray diffraction techniques in the cubic space group Pm ($) over bar 3m at 21(1)degrees C. Their structures were refined to the final error 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 which I > 3 sigma(I). In dehydrated Cd-6-A, six Cd2+ ions are found at two different 3-fold-axis sites near 6-oxygen-ring centers. Four Cd2+ ions 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 two extend 0.28 Angstrom into the large cavity from such planes. To prepare 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 cooling, to lower pressures at lower temperatures. In this structure, three Cd2+ ions lie near 6-ring centers where each coordinates to three framework oxygens at 2.27(1) Angstrom, Six Cd+ ions are found at three crystallographic 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); and 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 cavity 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 metal vapor into zeolite A has caused three of the six Cd-+(2) ions to be 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 symmetry in the large cavity.