We designate as “bridge-flipped isomers” those pairs of molecules that differ only in the orientation of a bridge of atoms connecting two major parts of the molecules. Examples are found among the benzylideneanilines, where the isomerism is Ar-CH=N-Ar’ vs. Ar-N=CH-Ar’, and among the phenylhydrazones, where the isomerism is Ar-NH-N=CH-Ar’ vs. Ar-CH=N-NH-Ar’ (Ar = aryl). Bridge-flipped isomers that are isomorphous (assuming identical solid-state molecular packing arrangements) may be capable of forming solid solutions over a wide range of component concentrations. Bridge-flipped isomers that are not isomorphous may be capable of serving as seeds for producing new polymorphs, isomorphous with the seeds, of their formerly nonisomorphous counterpart. Given their similarity in molecular size and shape, bridge-flipped isomers might be expected to be routinely isomorphous, but we have found reported examples of isomorphous pairs to be rare. We are searching for isomorphous pairs using single-crystal X-ray diffraction, following the premise that similar solid-state intermolecular interactions in the two isomers would encourage their isomorphism. As part of an investigation of halogen…nitrogen and halogen…halogen interactions potentially shared by these isomers, we have now determined the crystal structure of 2,3,4,5,6-pentafluoro-N-(4-pyridinylmethylene)benzenamine. In the solid state, molecules are linked into chains lengthwise by an R22(8) motif defined by C-F moieties and an R22(6) motif defined by pyridine ring nitrogen atoms and ring C-H moieties. Adjacent chains interact laterally through a different R22(8) motif defined by C-F moieties and also through a close C-F…H-C=N interaction involving the bridge. Although the ring motifs could be maintained in the bridge-flipped isomer of this compound, the C-F…H-C=N interaction is likely to be disrupted by the bridge flip. We are currently preparing this isomer to determine whether disrupting this latter interaction as a result of the bridge flip necessitates its assuming a different crystal structure.

Fluorine...fluorine and fluorine...hydrogen contacts in the crystal structure of a pentafluorinated benzylideneaniline

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.