Molecular Recognition in the Solid State: Hydrogen-Bonding Control of Molecular Aggregation

The design of molecular subunits that self-assemble into well-defined structures in the solid state is an area of intense current interest. A key to controlling the packing arrangement lies in manipulating the type and orientation of the noncovalent interactions between the subunits. The strong and directional nature of hydrogen bonds has led to their widespread use in self-assembling systems. In the solid state, rules have been delineated to allow the reasonable prediction of hydrogen-bonding packing patterns in crystals. This had led to a search for molecular components that because of their hydrogen-bonding characteristics will form persistent packing motifs in well-defined shapes or patterns. We have recently discovered that a strong bidentate hydrogen bonding interaction is formed between 2-amino-6-methylpyridine and carboxylic acids. Bis(2-amino-6-methylpyridine) derivatives and dicarboxylic acids will selfassemble into alternating cocrystal structures. The packing of the two components can be controlled in a rational way by changing the nature, size, and orientation of the spacer groups that link the hydrogen-bonding subunits.