Smart zeolites: new forms of tungsten and molybdenum oxides

Abstract

In this Account, the authors describe their recent research efforts involving the use of volatile hexacarbonylmolybdenum and -tungstem compounds, as precursors in the synthesis of highly organized assemblies of molecular dimension molybdenum and tungsten oxides, encapsulated within the diamond network of 13-[Angstrom] supercages found in zeolite Y. These assemblies are extremely uniform in terms of their nuclearity and structure, and their exclusive internal confinement inside of and lack of significant perturbation of the zeolite Y host. In these materials, the bulk form of the metal oxide has essentially been reconstituted within the nanoscale void spaces of a crystalline aluminosilicate framework host. The electronic and structural properties of these molecular metal oxide arrays can be easily manipulated as a result of their facile redox interconvertibility, and the further capability of fine tuning their electronic enviornment by choosing which charge-balancing cation is present in the supercage. Bulk forms of WO[sub 3] and MoO[sub 3], which possess octahedral building blocks arranged into open framework, layer, and tunnel structures, are probably most famous for their ability to reversibly accept metal cations and protons into their internal void spaces and electron-charge-transfer equivalents into their conduction bands. This fascinating property enables them to function as intelligentmore » materials in, for example, electrochromic windows, mirrors and displays, rechargeable solid-state batteries, pH-microelectrochemical transistors, and chemical sensors. In addition, their narrow-band-gap semiconductor properties allow them to be usefully exploited in liquid junction solar and electrochemical cells.23 refs., 5 figs., 1 tab.« less