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

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 (Tl 12 Si 12 Al 12 O 48: a = 12.153(4) Å, R 1 = 0.054, and R 2 = 0.060) and after the reaction, followed by washing with water and redehydration at 623 K (In 10 Si 12 Al 12 O 48 ·In: a = 12.098(2) Å, R 1 = 0.063, and R 2 = 0.062), have been determined by single-crystal X-ray crystallography at 294 K using the space group Pm 3 m . In In 10 −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 In 2+ (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 In 0 atom per unit cell, probably associated with In ions, is found at two quite unusual positions: one-half of an In 0 lies at the center of sodalite unit (In(6)) and the other half of the In 0 is opposite a 4-ring relatively deep in the large cavity (In(7)). The crystal structure of In 10 −A·In is viewed as a mixture of two kinds of “unit cells,” In 8 −A·In and In 12 −A·In, each with a cationic charge of 12+. By their approach distances to framework oxygens, the ionic radii of In + and In 2+ 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 (In 5 ) 8+ clusters (four In 2+ ions at In(2) with an In 0 atom at their center at In(6), In(2)−In(6) distance = 2.754(2) Å) in half of the sodalite units (In 8 −A·In), and bent (In 3 ) 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 (In 12 −A·In).