Topological Isomerism in Flexible Hydrogen-bonded Inclusion Frameworks

Michael D. Ward, Department of Chemical Engineering and Materials Science, University of Minnesota

A unique class of molecular host frameworks based on hydrogen-bonded sheets of guanidinium ions and sulfonate moieties of organodisulfonate "pillars" will be described that afford well-defined inclusion cavities with sizes, shapes and physicochemical characteristics that can be tuned systematically through control of the pillar structure. These cavities are occupied by guest molecules that actually serve as templates during the assembly of the frameworks. Lamellar architectures are especially persistent owing to the remarkable conformational flexibility of the hydrogen-bonded sheets and the organodisulfonate pillars. This flexibility, as well as a topological isomerism that produces numerous lamellar architectures, permits the host frameworks to conform to differently sized and shaped guest molecules, thereby providing a mechanism for achieving the cohesive energy that drives the formation of these materials. The persistence of the guanidinium-sulfonate hydrogen-bonded sheets also enables the formation of porous tubular architectures having the same supramolecular hydrogen-bonding connectivity as the lamellar phases. The lamellar and tubular structures are reminiscent of lamellar and hexagonal surfactant microstructures with respect to their structural characteristics and persistence.