TOPOTACTIC METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION IN ZEOLITE-Y - STRUCTURE AND PROPERTIES OF CH3MY FROM MOCVD REACTIONS OF (CH3)2MHY, WHERE M = ZN, CD

A mild and controlled synthetic route has been developed that quantitatively incorporates MOCVD-type precursors within the void spaces of zeolite Y. The process is illustrated with respect to the reactions of volatile, molecular dimethylcadmium and dimethylzinc with Bronsted acid sites in zeolite Y. Charge-balance and templating constraints of the host ensure that the sole reaction product CH3M (M = Cd, Zn) is exclusively housed in the supercages of zeolite Y with spatial and compositional uniformity throughout the entire host lattice. These anchored CH3M species are perfectly poised for assembly reactions with volatile chalcogenide reagents to form ordered superlattices of II-VI semiconductor nanoclusters. The geometry, site location, and occupancy of anchored CH3M have been determined by Rietveld analysis of low-temperature synchrotron powder X-ray diffraction data. For samples chemically analyzed as containing 44 CH3M moieties per unit cell of zeolite Y, almost equal numbers of CH3M Species are found to be anchored via the metal center to framework oxygens at sites II and III, located exclusively in the supercage. The transformation from HY to CH3MY host has been conveniently monitored by in situ mid-IR and far-IR spectroscopy. Distinctive vibrational modes are assignable to intrazeolite (CH3)2M, anchored CH3M, and evolved CH4 species. Room temperature C-13 and Cd-113 static and MAS-NMR studies of these species reveal that they are undergoing motion on the NMR time scale in the supercages of zeolite Y. Observed NMR chemical shifts are consistent with primary anchoring interactions between the metal center and the oxygen framework for both chemisorbed (CH3)2MNaY and anchored CH3MY species. In the case of the former, Na-23 MAS-NMR spectroscopy reveals the existence of a secondary anchoring interaction between supercage site II Na+ cations and the nucleophilic methyl groups of the (CH3)2M guest.