No 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, 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) 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 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).

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) Å, crystal 1) and that after washing and redehydration (In87Si100Al92O384, Fd3̄m with a = 24.916(3) Å, 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 R 1 = 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 “In5 8+”; In5 7+, 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).

A spatially ordered quantum dot array of cationic indium nanoclusters has been synthesized in a single crystal of zeolite X. A single crystal of fully dehydrated and fully indium-exchanged zeolite X (ca. In 87 Si 100 Al 92 O 384 , In 87 -X) was exposed to 0.5 atm of H 2 S for 12 h at 673 K. After it was evacuated at temperature and cooled to 294 K, the crystal structure of the product (ca. In 66 Si 100 Al 92 O 384 , In 66 -X, a ) 24.942(4) Å) was determined by single crystal X-ray diffraction techniques in the cubic space group Fd3 hm. It was refined with all measured reflections to the final error index R 1 ) 0.058 for the 754 reflections with F o > 4σ(F o ). X-ray photoelectron spectroscopy experiments confirmed the existence of both atomic and cationic indiums inside the single crystal. The 66 indium atoms or ions per unit cell were found at four crystallographically distinct positions, all on 3-fold axes. Eight In atoms at the sodalite unit centers and 32 In ca.2+ ions nearby (In ca.2+ -In 0 ) 2.683(1) Å), both filling their crystallographic sites, form eight (In 5 ) n+ (n ) 7 satisfies Lewis's rule) per unit cell, one per sodalite cavity. Each (In 5 ) n+ quantum dot (diameter ca. 7.0 Å) is held in place by 12 strong electrostatic interactions with six ring oxygens (In ca.2+ -O(3) ) 2.170(7) Å). These quantum dots are arranged in the diamond structure with intercluster distances of ca. 10.8 Å. This crystal (cross-section ca. 0.15 mm) contains ca. 300 Tera (10 12 ) ordered dots of (In 5 ) n+ . Another 25 In + ions per unit cell were located at a 32-fold site in the supercage, and a single In 2+ ion was found nearby. Treatment with H 2 S has allowed In + ions to disproportionate to give full occupancy at the (In 5 ) n+ site.

The structure of a single crystal of dehydrated zeolite Na−X selected from a batch grown by Petranovskii in Russia, of composition Na92Si100Al92O384 per unit cell, was determined by X-ray diffraction methods in the cubic space group Fd3̄; a = 25.077(4) Å at 21 °C. R 1 = 0.054 for the 320 reflections for which F o > 4σ(F o); wR 2 based on F 2 and all data is 0.140. Na+ ions are found at four crystallographic sites. Sites I‘ and II are fully occupied with 32 Na+ ions each. The remaining 28 Na+ ions partially occupy two 12-ring (site III‘) positions with 10(4) near an O−Al−O sequence and 18(4) near an O−Si−O sequence. These results differ from those of the two previous investigations of dehydrated Na−X, which, in turn, disagree substantially with each other. The near energy equivalence of two (or more) III‘ sites, the presence of an impurity cation in one determination, and a consideration of the differing qualities of the diffraction data are sufficient to reconcile all results. The substitution of four silicon atoms per unit cell into the aluminum equipoint necessarily has a complicating effect. Considerations involving the ordering of these substituted silicon atoms are not needed.