Crystal Structure of Dehydrated Partially Ag+-Exchanged Zeolite A, Ag4.6Na7.4-A, Treated with Hydrogen at 350?é

摘要

The crystal structure of Ag4.6Na7.4-A, dehydrated, treated with H2, and evacuated, all at 350∩, has been determined by single crystal x-ray diffraction methods in the cubic space group Pm3m at 24(1)∩; a = 12.208(2)∈. The structure was refined to the final error indices R1 = 0.088 and R2 (weighted) = 0.069 using 194 independent reflections for which I0 > 3ヲ(I0). On threefold axes near the centers of 6-oxygen rings, 7.4 Na+ ions and 0.6 Ag+ ions are found. Two non-equivalent 8-ring Ag+ ions are found off the 8-ring planes, each containing about 0.6 Ag+ ions. Three non-equivalent Ag atom positions are found in the large cavity, each containing about 0.6 Ag atoms. This crystallographic analysis may be interpreted to indicate that 0.6 (Ag6)3+ clusters are present in each large cavity. This cluster may be viewed as a nearly linear trisilver molecule (Ag3)0 (bond lengths, 2.92 and 2.94 ∈; angle, 153∑) stabilized by the coordination of each atom to a Ag+ ion at 3.30, 3.33, and 3.43 ∈, respectively. In addition, one of the silver atoms approaches all of the 0(1) oxygens of a 4-ring at 2.76∈. Altogether 7.4 Na+ ions, 1.8 Ag+ ions, and 1.8 Ag atoms are located per unit cell. The remaining 1.0 Ag+ ion has been reduced and has migrated out of the zeolite framework to form silver crystallites on the surface of the zeolite single crystal.