Extensive intrazeolitic hydrolysis of Zn(II): partial structures of partially and fully hydrated Zn(II)-exchanged zeolite X

Complete Zn2+ exchange of two single crystals of zeolite X(Na92Si100Al92O384) was attempted at 80 degreesC from aqueous Zn(NO3)(2) (pH = 5.5 at 23 degreesC). The structures of crystal 1 (partially dehydrated by evacuation at 23 degreesC and 10(-3) Torr for two days) and crystal 2 (fully hydrated) were determined by X-ray diffraction techniques in the cubic space group Fd3 at 23 degreesC (a(o) = 24.750(5) and 24.872(6) Angstrom, respectively). They were refined using all intensities to the final error indices R-1 = 0.126 and 0.116 based on the 428 and 348 reflections, respectively, for which F-o > 4 sigma (F-o). Each crystal has about 54 Zn2+ ions per unit cell, indicating the uptake of eight excess Zn(OH)(2) molecules. In both crystals, further extensive hydrolysis of Zn2+ is seen. Many non-framework oxygens were not found. In crystal 1, 34 Zn2+ ions per unit cell occupy conventional cationic sites: 10 are at site I', 12 at site II, and 12 at site III'. Three Zn2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercages. Three Zn2+ ions at the centers of sodalite cavities each coordinate tetrahedrally to four non-framework oxygens to give (likely) Zn(OH)(2)(H2O)(2) which hydrogen bonds multiply to the zeolite framework. At three supercage positions, about 14 Zn2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 37 H3O+ ions are found: 20 at site I' and 17 at site II. It is presumed, considering the number of H3O+ ions, that the latter 14 Zn2+ ions are hydrolyzed Zn2+ ions, likely hydrated Zn(OH)(2) molecules, some likely bridging. In crystal 2, 33 Zn2+ ions per unit cell are found at conventional cationic sites: two at site I, 14 at two different sites I', seven at site II, and 10 at site III'. As in crystal i, three Zn2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercage. At three supercage positions, about 18 Zn2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 40 H3O+ ions are found: 18 at site II' and 22 at site II. Only about 16 non-framework oxygens were found per unit cell: eight water molecules in the supercages and, in the sodalite cages, eight hydroxide ions which participate in the formation of two nearly cubic Zn-4(OH)(4)(4+) clusters. (C) 2000 Elsevier Science B.V. All rights reserved.