ZEOLATES - A COORDINATION CHEMISTRY VIEW OF METAL-LIGAND BONDING IN ZEOLITE GUEST HOST INCLUSION-COMPOUNDS

Various guests have been investigated in zeolite hosts in our laboratory over the past five years. From analysis of in situ spectroscopic observations (FT-IR, UV-vis, Mossbauer, DOR-MAS NMR) of the reaction sequences and structural features of precursors and products (EXAFS, Rietveld refinement of powder XRD data), the molecule size cavities and channels of zeolites respectively are viewed as providing macrospheroidal and macrocylindrical, multisite multidentate coordination environments toward encapsulated guests. By thinking, in particular, about the alpha- and beta-cages of the zeolite Y host effectively as a "zeolate' ligand composed of interconnected and perfectly organized anionic aluminosilicate 'crown ether-like" rings, the materials chemist is able better to understand and exploit the reactivity and coordination properties of the zeolite internal surface for the anchoring and self-assembly of a wide range of encapsulated guests (e.g., metal atoms, metal cations, metal clusters, coordination compounds, metal carbonyls, organometallics, metal oxides, and semiconductor nanoclusters. This approach helps with the design of synthetic strategies for creating novel guest-host inclusion compounds having possible applications in diverse areas of materials science, such as size/shape selective catalysis, nonlinear optics, quantum electronics, and photonics. To present this 'crown ether-zeolate ligand analogy", we will focus attention on structurally well-defined examples of metal-zeolate bonding, involving mainly metal carbonyls and molecular metal oxides, housed within the diamond network of interlaced 13-angstrom supercages (alpha-cages) of zeolite Y, mainly taken from our recent work. A coordination chemistry view of metal-zeolate bonding in intrazeolite metal organic chemical vapor deposition type precursors and semiconductor nanocluster products is presented in a separate publication.20