文摘
The structures of the subnanometer clusters of CdS that form in zeolite Y (FAU), prepared as follows, have been determined. A single crystal of Cd2+-exchanged zeolite Y was prepared by the exchange of Na75–Y (|Na75|[Si117Al75O384]–Y with aqueous Cd(NO3)2 at 294 K, followed by vacuum dehydration at 723 K (crystal 1). A second crystal, similarly prepared, was exposed to 6.7 × 104 Pa of dry H2S(g) for 6 h at 294 K and evacuated (crystal 2). Their structures were determined crystallographically using synchrotron X-rays and were refined using all data to the final error indices (calculated using only Fo > 4σ(Fo)) of R1/wR2 = 0.040/0.156 and 0.049/0.186, respectively. In crystal 1, Cd2+ ions primarily occupy sites I and II. In crystal 2, |Cd27(Cd4S6+)0.6(Cd(SHCd)46+)0.9H12|[Si117Al75O384]–FAU, tetrahedral Cd4S6+ ions center about 7.5% of the sodalite cavities and tetrahedral Cd(SHCd)46+ ions center about 11% of the supercages. In Cd(SHCd)46+, a Cd2+ ion at the center of a supercage bonds tetrahedrally to four SH– ions, each of which bonds in turn to an 8-ring Cd2+ ion. Of the 36.5(9) Cd2+ ions per unit cell (indicating complete or nearly complete Cd2+ exchange) before treatment with H2S(g), only 6.9 participate in the above clusters. Most, 27, remain uncomplexed, and 2.6 have left the zeolite as CdS(s). No neutral clusters of formula CdnSn are present within the zeolite.
