HYDROGEN-BONDS AS DESIGN ELEMENTS IN ORGANIC-CHEMISTRY

This work involves the use of crystal chemistry and crystallographic data base analyses as a way to study hydrogen-bond directed molecular recognition properties of organic molecules. By using the solid phase rather than solution, our studies are not limited to tightly bound dimeric species but encompass aggregate structures with multiple molecules, intricate interlinked patterns, and both strong and weak (often very weak) intermolecular interactions. The point of view taken here is to analyze the consequences of directed and selective hydrogen-bond interactions on sets of molecules rather than focusing on the energy or geometry of individual hydrogen-bond interactions. The "consequences" are to a solid-state chemist what a new synthesis is to a solution chemist, i.e., the formation of new chemical species. Methods for deriving hydrogen-bond rules from large sets of crystal structures are presented here. Ways to prepare organic cocrystals and to use cocrystallization to probe the forces involved in aggregation phenomena are discussed, and examples are given of how molecular aggregation can impart unexpected new properties to organic compounds.