W0183
Crystal Engineering Through Charge Transfer Interactions. W.T. Pennington,[dagger] R.D. Bailey,[dagger] B.T. Holmes,[dagger] L.L. Hook,[dagger] M. Warmoth,§ R.P. Watson,[dagger] and T.W. Hanks§, [dagger]Department of Chemistry, Clemson University, Clemson, SC 29634-1905, §Department of Chemistry, Furman University, Greenville, SC 29613
The use of n->[sigma]* charge transfer interactions for crystal engineering applications will be discussed. Like hydrogen bonding, these interactions are selective, directed and relatively strong. Unlike most hydrogen bonded structures, however, the donor and acceptor sites are rarely present in the same molecule, so most structures based on this interaction are donor·acceptor complexes. This offers the advantage that either the donor or the acceptor can serve as a removable structural template. One focus of our work has been to utilize this aspect for the isolation and interconversion of polymorphic donor molecules. For example, thermal decomposition of iodine complexes of tetrapyridylpyrazine (tpp) of two different stoichiometric ratios (tpp·I2 and tpp·2I2) lead to different polymorphs of tpp, and allows for interconversion between the two forms. We are currently investigating a variety of polymorphic systems to test the utility of this method. Most of our work thus far has centered on iodine as the acceptor molecule, but we are also exploring the effect that other small acceptor molecules may have on the decomposition pathway.
Another area of interest for crystal engineering applications are coordination polymers based on d10 metal halides. Nitrogen heterocycles, such as pyrazine, bridge metal halide chains to form extended layers. Recently, we have incorporated Lewis acid guest molecules into these structures through interactions involving the halides of the metal halide chains as donors. The use of these guest molecules as structure controlling templates for the formation of microporous solids is being pursued.
Results and future work in both these areas will be described.