Two Crystal Structures of Dehydrated Ag+ and Rb+ Exchanged Zeolite A, Ag12-xRbx-A, x = 2 and 3.

Two crystal structures of dehydrated and exchanged zeolite A, stoichiometries of (a = 12.278(2)) and (a = 12.286(2)) per unit cell, have been determined by single crystal x-ray diffraction techniques. Their structures were solved and refined in the cubic space group Pm3m at 21(1)C. The crystals of and were prepared by flow methods using exchanged solution in which mole ratios of AgNO and RbNO were 1:5 and 1:50, respectively, with the total concentration of 0.05 M. The structures of the dehydrated and the were refined to the final error indices, = 0.064 and = 0.060 with 291 reflections, and = 0.063 and = 0.080 with 416 reflections respectively, for which I >3(I). In both structures, one reduced silver atom per unit cell was found inside the sodalite cavity. It may be present as a hexasilver cluster in 1/6 of the sodalite units or as an isolated Ag atom coordinated to 4 ions in each sodalite unit to give , symmetry 4 mm. In the structure of dehydrated , 8 ions lie on the threefold axis and each is nearly at the center of the 8-rings at the sites of symmetry. In the structure of dehydrated , two crystallographically different eight 6-ring ions were found; ions in the (111) planes of their O(3) framework oxygens and one ion inside of sodalite cavity. Two crystallographically different 8-ring cations were also found; two ions at the centers of the 8-oxygen rings and one ion into the large cavity. Both structures indicate that ions prefer to occupy the 8-ring sites, while ions prefer to occupy the 6-ring sites.