HYDROGEN-BONDED SCAFFOLDING FOR CRYSTAL ENGINEERING. Christer B. Aakeröy, Mark Nieuwenhuyzen, School of Chemistry, The Queen's University of Belfast, Belfast, Northern Ireland

The intentional design and synthesis of specific structural aggregates in the solid state, crystal engineering, continue to attract considerable attention, since the controlled assembly of structural units into a crystal may result in the development of new materials with cf. improved electrical, optical or catalytic properties. Unfortunately, the task of directing the orientation of individual molecules into one, two and, finally, three-dimensional architectures is extremely difficult, as they can adopt a vast number of conformations in the crystal.

We have combined the strength and directionality of the hydrogen bond with suitable carboxylic acids, e.g. tartaric acid¹ and malic acid,² in the design of predictable, two-dimensional ionic architectures. In these structures, the anionic building blocks provide structural consistency and rigidity by creating anionic layers held together by several directional O-H...O hydrogen bonds. The infinite layers then act as `scaffolding', thereby restricting the possible packing options for the cations. Within this structural framework, the cation can act either as a `bridge' between neighbouring layers, or as a `spacer', depending upon its chemical characteristics, thereby providing an extension from 2-D to 3-D motifs.

The close similarity between the structural behaviour of the two acids, and the complementarily and selectivity of their respective hydrogen-bond sites, has also enabled us to incorporate tartaric acid and malic acid within the same solid framework as one cocrystal.³

l. C. B. Aakeröy; P. B. Hitchcock, J. Mat. Chem., 1993, 3, 1129.

2. C. B. Aakeröy; M. Nieuwenhuyzen, J. Am. Chem. Soc., 1994,116, 10983.

3. C. B. Aakeröy; T. I. Cooke; M. Nieuwenhuyzen, Supramolecular Chemistry, 1996, in the press.