Crystal structures of fully indium-exchanged zeolite X

Fully indium-exchanged zeolite X has been prepared by solvent-free redox ion-exchange of fully dehydrated fully Tl⁺-exchanged zeolite X with In metal at 350°C. Electron-probe microanalysis and single-crystal X-ray diffraction showed the product to be an indium aluminosilicate (ca. 47 wt% In) free of thallium. The crystal structure of the initial product (In₈₈Si₁₀₀Al₉₂O₃₈₄, Fd3̄ with a = 24.913(2) angstrom, crystal 1) and that after washing and redehydration (In₈₇Si₁₀₀Al₉₂O₃₈₄, Fd3̄m with a = 24.916(3) angstrom, crystal 2) were determined by single-crystal X-ray crystallography at 21°C. They were refined with all measured reflections to the final error indices R₁ = 0.058 and 0.045 for the 615 and 337 reflections, respectively, with F_o > 4σ(F_o). In each unit cell of crystal 1, 88.0 indium atoms or ions are distributed over eight crystallographically distinct positions (for crystal 2, 87.0 and seven). Among those, 63.0 indium ions or atoms are found at four nonequivalent 3-fold axis equipoints: 29.0 In⁺ ions almost fill site II, 24.0 In⁺ and 8.0 'In²⁺' ions completely fill site I′, and 2.0 In⁰ atoms are found at sodalite unit centers. For crystal 2, the corresponding results are 66.5, 32.0 fill site II, 22.0 + 10.0 fill site I′, and 2.5. Each of the In⁰ atoms associates with four tetrahedrally arranged 'In²⁺' ions to give 'In₅⁸⁺'; In₅⁷⁺, an even species with an octet of electrons about the central In, is more likely. At four distinct site III′ (supercage) positions, 25.0 In⁺ ions are found in crystal 1 (20.5 at three positions for crystal 2).