Complete Redox Exchange of Indium for Tl+ in Zeolite A. Crystal Structures of Anhydrous Tl12−A and In10−A·In. Indium Appears as In2+, In+, and In0. The Clusters (In5)8+ and (In3)2+ Are Proposed

Abstract

Indium has replaced all of the Tl+ ions in fully dehydrated fully Tl+-exchanged zeolite A by a solvent-free redox ion-exchange reaction with In metal at 623 K. The crystal structures of the zeolite before (Tl12Si12Al12O48: a = 12.153(4) Å, R1 = 0.054, and R2 = 0.060) and after the reaction, followed by washing with water and redehydration at 623 K (In10Si12Al12O48·In: a = 12.098(2) Å, R1 = 0.063, and R2 = 0.062), have been determined by single-crystal X-ray crystallography at 294 K using the space group Pm3m. In In10−A·In, 11 In atoms or ions/unit cell are distributed over seven crystallographically distinct positions. Seven In ions occupy 3-fold-axis equipoints: four In+ ions lie opposite 6-rings in large cavity (In(1)), and two In2+ (In(2)) and one In+ (In(3)) lie opposite 6-rings in the sodalite unit. Three In+ ions per unit cell are found at two different 8-ring positions: 1.5 on the 8-ring plane (In(4)) and 1.5 off (In(5)). Finally, one In0 atom per unit cell, probably associated with In ions, is found at two quite unusual positions: one-half of an In0 lies at the center of sodalite unit (In(6)) and the other half of the In0 is opposite a 4-ring relatively deep in the large cavity (In(7)). The crystal structure of In10−A·In is viewed as a mixture of two kinds of “unit cells,” In8−A·In and In12−A·In, each with a cationic charge of 12+. By their approach distances to framework oxygens, the ionic radii of In+ and In2+ are ca. 1.23 and 1.04 Å, respectively. The In(6) and In(7) positions lie deep within cavities where they approach only In cations. This suggests the existence of tetrahedral (In5)8+ clusters (four In2+ ions at In(2) with an In0 atom at their center at In(6), In(2)−In(6) distance = 2.754(2) Å) in half of the sodalite units (In8−A·In), and bent (In3)2+ clusters (In(1)−In(7)−In(1) angle = 148.0(9)° and In(1)−In(7) = 3.073(8) Å) in half of the large cavities (In12−A·In).