Molecular Recognition in the Solid State: Controlled Assembly of Hydrogen-Bonded Molecular Sheets

A novel hydrogen-bonding motif for the control of solid-state structures has been developed. The motif is based on the hydrogen bonding complementarity of carboxylic acids with 2-aminopyridine derivatives. Linking two aminopyridine groups through a rigid aromatic spacer provides a receptor unit that can complex dicarboxylic acids. When there is a good correspondence between the length of the spacer and that of the carboxylic acid, a discrete 1:1 complex is formed. When the dicarboxylic acid is longer than the receptor, an alternating hydrogen-bonded cocrystal occurs with the carboxylates on each diacid binding to different receptors. This motif dominates the cocrystal, forming even when the relative lengths of the diacid and the receptor change. Within the constraints of the alternating ribbon structure, the spatial position of the two components can be varied in a well-defined and predictable manner.