Intermolecular interactions in phenylhydrazone crystals: Lewis acid-Lewis base vs. hydrogen bonding

CHED 413

Trina M. Arola, tmarola@stthomas.edu and William H. Ojala, whojala@stthomas.edu. Department of Chemistry, University of St. Thomas, 2115 Summit Avenue, St. Paul, MN 55105
We are working toward preparing new crystalline materials by co-crystallizing molecules we have designated “bridge-flipped isomers.” In these isomers, two major parts of the molecule are joined by a bridge of atoms; changing the bridge orientation relates one isomer to the other. We are currently examining phenylhydrazones, in which the bridge-flipped isomerism is Ar-NH-N=CH-Ar' vs. Ar-CH=N-NH-Ar' (where Ar = aryl). Co-crystallization would be facilitated if the bridge-flipped isomers were isostructural (same molecular packing arrangement). We are determining the solid-state structures of phenylhydrazones by single-crystal X-ray diffraction to identify isostructural bridge-flipped isomeric pairs for future co-crystallization experiments. Intermolecular interactions linking molecules into similar chains in the two solid isomers might encourage their isostructuralism, so we have prepared phenylhydrazones substituted with halogen atoms and nitrile groups to encourage intermolecular Lewis acid-Lewis base interactions. We find H-bonding between the bridge N-H and the nitrile group to be a competing and differentiating interaction.