Complete redox exchange of indium for Tl+ in zeolite A. Crystal structures of anhydrous Tl-12-A and In-10-A center dot In. Indium appears as In2+, In+, and In-0. The clusters(In-5)(8+) and (In-3)(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 (Tl12Si12-Al12O48: a = 12.153(4) Angstrom, R-1 = 0.054, and R-2 = 0.060) and after the reaction, followed by washing with water and redehydration at 623 K (In10Si12Al12O48. In: a = 12.098(2) Angstrom, 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 Pm3m. 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 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(ln(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 In2+ are ca. 1.23 and 1.04 Angstrom, 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 In2+ ions at In(2) with an In-0 atom at their center at In(6), In(2)-In(6) distance = 2.754(2) Angstrom 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)(0) and In(1)-In(7) = 3.073(8) Angstrom) in half of the large cavities (In-12-A . In).