Crystal Engineering: Solvent Induced Polymorphs Using Kemp's Triacid, A Facial Amphiphile. Karl S. Hagen and Scott L. Childs, Department of Chemistry, Emory University, Atlanta, GA 30322

The synthesis of new structures of Kemp's triacid, combines supramolecular chemistry and crystal engineering, and the results show how an organized organic system can be manipulated in the solid state.

Kemp's triacid (KTA), a facial amphiphile with rigid, pre-organized carboxylates crystallizes as a simple supramolecular organization (see Figure). The individual molecules of KTA are hydrogen bonded to each other form 1-D structures having an I-beam like cross section. These rods pack in a co-linear fashion with orthogonal cross-sections in the crystal. By identifying the rod packing motif as a stable supramolecular synthon, new structures have been synthesized using a component mediated structural variation approach. Flat organic solvent molecules such as benzene, co-crystalized with KTA, induce a re-orientation of the rod synthon such that their cross sections are parallel. The linear solvent molecule acetonitrile, induces a different hydrogen bonded interaction between neighboring KTA molecules so that 2-D bilayers form.

Rebek, J., Jr.; Marshall, L.; Wolak, R.; Parris, K.; Killoran, M.; Askew, B.; Nemeth, D.; Islam, N. J. Am. Chem. Soc. 107, 7476-7481 (1985)