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Directed Synthesis of Nanoporous Coordination Solids

Omar M. Yaghi

Department of Chemistry and Biochemistry
Arizona State University
This is an abstract for a poster to be presented at the Fifth Foresight Conference on Molecular Nanotechnology.

The assembly of porous frameworks by linking organic and inorganic molecular building blocks into extended 1-D, 2-D and 3-D networks offers many attractive opportunities for designing the topology and functionalizing the pores. Currently, at least three challenges exist in establishing the synthetic chemistry and utility of porous coordination solids. Firstly, attempts to prepare materials with large pores has resulted in self-inclusion of the assembled frameworks thus preventing access to the voids. Secondly, in cases where the achievement of open frameworks has been possible, removal of the guest species results in the destruction of the framework. Thirdly, the assembly reactions often produce either poorly crystalline or amorphous solids thus precluding their full characterization. In this presentation, our approach to resolving these issues including our most recent success in this direction will be outlined and discussed.

Cationic, anionic and neutral porous networks constructed from transition metal ions and highly symmetric organic molecules such as 4,4'-bipyridine (4,4'-bpy) and 1,3,5-benzenetricarboxylic have been prepared. Single crystals of these materials have been obtained by either performing the assembly reaction in gel media or hydrothermally in the temperature range 100-150 °C. Interpenetration has been prevented by using large hydrogen-bonded aggregates as the guest species to fill the voids, which has resulted in the construction of open-frameworks having pore dimensions of up to 35 Å. Molecular and ionic guests can be removed or exchanged from the pores to allow the inclusion of other species into the channels. In this way, channels capable of the selective inclusion of aromatics, alcohols, and anions have been tailored. We have found that such processes occur with high selectivity due to the presence of coordinatively unsaturated metal ions and weak intermolecular forces operating within the pores. This presentation will show that 1-D, 2-D and 3-D networks can be prepared as porous solids capable of reversible binding of guests and selective inclusion that is not only based on shape and size of incoming guests but also on their electronic affinity to the channels. The synthesis, structure and inclusion properties of these solids including strategies for decorating the channels with organic (pi)-systems and coordinately unsaturated metal centers will be presented.


*Corresponding Address:
Omar M. Yaghi, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604. Phone: (602) 965-0057; Fax: (602) 965-2747. E-mail: oyaghi@asu.edu
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