Synthesis and Crystal Structure of Ag4I4 Nanoclusters in the Sodalite Cavities of Fully K+-Exchanged Zeolite A

Abstract

Ag4I4 nanoclusters have been synthesized in half of the sodalite cavities of fully K+-exchanged zeolite A. An additional KI molecule is retained in each large cavity as part of a near square planar K4I3+ cation. A single crystal of Ag12-A, prepared by the dynamic ion-exchange of Na12-A (LTA) with aqueous 0.05 M AgNO3 and washed with CH3OH, was placed in a stream of flowing 0.05 M KI in CH3OH at 294 K for 2 days. The crystal structure of the product, K9Si12Al12O48·(Ag4I4)0.5·K4I3+, a = 12.290(1) Å, was determined by single-crystal X-ray diffraction in the cubic space group Pm3̄m. It was refined with all measured reflections to the final error index R1 = 0.077 (based on the 264 reflections for which Fo > 4σ(Fo)). The thirteen K+ ions per unit cell are found at three crystallographically distinct positions: eight K+ ions in the large cavity fill the 6-ring site, three K+ ions fill the 8-rings, and two K+ ions are opposite 4-rings in the large cavity. One iodide ion per unit cell lies opposite a 4-ring in the large cavity, held there by two 8-ring and the two 6-ring K+ ions (K4I3+). Two Ag+ and two I- ions per unit cell are found on 3-fold axes in the sodalite cavity, indicating the formation of Ag4I4 clusters (interpenetrating tetrahedra; symmetry Td; diameter ca. 8.0 Å) in half of the sodalite units. Each cluster (Ag−I = 2.97(2) Å) is held in place by the coordination of its four Ag+ ions to the zeolite framework (each Ag+ cation is 2.48(1) Å from three 6-ring oxygens) and by the coordination of its four I- ions to large-cavity K+ ions through 6-rings (I−K = 2.72(6) Å).