CRYSTAL-STRUCTURE OF INDIUM-EXCHANGED ZEOLITE-A CONTAINING SORBED DISULFUR

Molecules of S-2 are sorbed by dehydrated fully indium exchanged zeoli te A from S(g) at 623 K. The crystal structure of dehydrated In8Si12Al 12O48.(In)(0.75)(S-2) (R-1 = 0.053, R-2 = 0.050, and a = 12.090(2) Ang strom) has been studied by single-crystal X-ray diffraction methods at 294 K using the space group <Pm(3)over bar m>. The complex structural results are interpreted as follows. Each unit cell contains eight ind ium cations, 0.75 indium atoms, and two sulfur atoms. Six In ions per unit cell are found at four nonequivalent 3-fold axis equipoints: two In+ ions and 0.5 In3+ ions lie opposite six-rings in the large cavity, and three In2+ ions and 0.5 In+ ions Lie opposite six-rings in the so dalite unit. Two In+ ions per unit cell are found at eight-ring positi ons, off the plane. Three-quarters of an indium per unit cell, as near -neutral atoms associated with In2+ cations, are found at the centers of the sodalite units. The distances of In+, In2+, and In3+ to the nea rest framework oxygens are ca. 2.55, 2.37, and 2.26 Angstrom, respecti vely. The structure may be viewed as having two kinds of ''unit cells. '' Unit cell 1 (In-8-A .(In)(S-2), 75%) contains the (In-5)(8+) cluste r (four In2+ ions tetrahedrally arranged about an In-0 in the sodalite unit (In2+-O = 2.37(1) Angstrom and In-0-In2+ = 2.75(2) Angstrom)). U nit cell 2 (In-8-A .(S-2), 25%) has two In3+ ions. In each large cavit y, one atom of a disulfur molecule (S-S = 2.13(13) Angstrom) associate s with three framework oxygens at 3.11(11) Angstrom, and the other sul fur atom bridges between two In+ ions at 3.26(3) and 3.37(19) Angstrom .