Crystal structure of a hydrogen sulfide sorption complex of fully Ca2+-exchanged zeolite X

The crystal structure of a hydrogen sulfide sorption complex of dehydrated 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)degrees 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 hydrogen sulfide gas at 21(1)degrees C. The structure was determined in this 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 the double six-rings, and the remaining 30 are at site II in the supercages. All 46 are octahedral. Each site-IL Ca2+ ion is recessed 0.84 Angstrom 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 sorption. (C) 1998 Elsevier Science B.V. All rights reserved.