Disproportionation of an Element in a Zeolite. I. Crystal Structure of a Sulfur Sorption Complex of Dehydrated, Fully Cd~(2+)-Exchanged Zeolite X. Synthesis of Tetrahedral S_4~(4+) and n-S_4~(2+), Two New Polyatomic Cationic of Sulfur

摘要

The crystal structure of a sulfur sorption complex of fully dehydrated, fully Cd~(2+)-exchanged zeolite X, Cd_(46)Si_(100)Al_(92)O_(384)·52S per unit cell (a = 24.925(7) A), has been determined by single-crystal X-ray diffraction method in the cubic space group Fd(3-bar) at 21(1) ℃. The crystal was prepared by ion exchange in an aqueous stream 0.05 M in Cd~(2+), followed by dehydration at 450 ℃ and 2 * 10~(-6) Torr and then exposure in situ to zeolitically dry sulfur vapor. The structure was refined to the final error indices R_1 = 0.051 and R_2 = 0.043 with 362 reflections for which I > 3σ(I). Forty-six Cd~(2+) ions are found at five crystallographic sites: 12 at site I at the centers of the hexagonal prisms (Cd - O = 2.387(8)), 8 at site I' in the sodalite cavities near the hexagonal prisms (Cd - O = 2.325(7) A), 7 at site II' in the sodalite cavities (Cd - O = 2.195(8) A), and the remaining 19 at two different site II positions, near single six-oxygen rings in the supercages, with occupancies of 7 and 12 (Cd - O = 2.155(7) and 2.251(7) A, respectively). All first-two sulfur atoms disproportionated upon sorption to give sulfide anions and two new tetrasulfur cations, S_4~(4+) and n-S_4~(2+). Each of 12 sulfide ions coordinates at a site II Cd~(2+) ion in the supercage. S_4~(4+) is tetrahedred with S - S = 2.17(2) A, a quantum mechanical calculation gives 2.21 A, and two of the eight sodalite cavities per unit cell are centered by one. In S_4~(4+), each sulfur atom is 3.380(9) A from three framework oxygens; with those 12 contacts, S_4~(4+) is hosted and stabilized by an anionic sodalite cavity. Each supercage holds a zigzag n-S_4~(2+) cluster with a torsion angle of 114(8)°. n-S_4~(2+) is electron deficient, bridges covalently between two zeolite oxygens, and has a predominantly ionic interaction with sulfide ion.