CRYSTAL-STRUCTURE OF A HYDROGEN-SULFIDE SORPTION COMPLEX OF FULLY CA2-EXCHANGED ZEOLITE-X()

The crystal structure of a hydrogen sulfide sorption complex of dehydr ated fully Ca2+-exchanged zeolite X, Ca46Si100Al92O384 . ca. 149H(2)S [a = 24.864(5) Angstrom], has been determined by single-crystal X-ray diffraction methods in the cubic space group Fd (3) over bar at 21(1)d egrees C. A crystal of Ca-46-X was dehydrated at 380 degrees C and 2 x 10(-6) Torr for two days, followed by exposure to 200 Torr of dry hyd rogen sulfide gas at 21(1)degrees C. The structure was determined in t his atmosphere and was refined to the final error indices R-1 = 0.073 and R-2 = 0.067 with 407 reflections for which I> 3 sigma(I). In this structure, 16 Ca2+ ions per unit cell fill site I at the centers of th e double six-rings, and the remaining 30 are at site II in the superca ges. All 46 are octahedral. Each site-IL Ca2+ ion is recessed 0.84 Ang strom into the supercage from the plane of the three oxygens to which it binds [Ca-O=2.373(9) Angstrom] and coordinates at 3.12(3) Angstrom to three H2S sulfur atoms in the supercage. Each of the remaining ca. 59 H2S 'hydrogen bonds' to two 12-ring oxygens [S-O = 3.27(6) Angstrom and O-S-O = 95.6(13)degrees], (nearly) filling all 12-rings with four H2S molecules each. The H2S molecules have not dissociated upon sorpt ion. (C) 1998 Elsevier Science B.V. All rights reserved.