Bridge Orientation as a Selector of Intermolecular Interactions in a Series of Crystalline Isomeric Benzylideneanilines

Abstract

Comparison of the crystal structures of compounds we have designated "bridge-flipped isomers," which on the molecular level differ only in the orientation of a bridge of atoms connecting two larger parts of the molecule, offers a useful context for the examination and evaluation of intermolecular interactions and their robustness as supramolecular synthons. Intermolecular interactions in the crystal structures of five pairs of bridge-flipped isomeric benzylideneanilines are examined here, including interactions between nitrile groups and ring hydrogen atoms, between halogen atoms, and between nitrile groups and halogen atoms. Of these, only the halogen-nitrile interaction in which the halogen is iodine is present in both bridge-flipped isomers of the pair, although its influence on the molecular packing arrangement is insufficient to compel the two isomers to assume identical packing arrangements. Pairwise analysis of crystal structures of bridge-flipped isomers thus provides a perspective beyond that provided by the isolated analysis of the structures of the individual compounds.

Competing intermolecular interactions in some `bridge-flipped' isomeric phenylhydrazones

“…Although this strategy in our own laboratory has yet to produce an isomorphous pair of 'bridge-flipped' isomers, it has allowed us to examine the variety of motifs in which nitrile groups and halogen atoms engage, whether separately or with each other. In previous reports, we have examined intermolecular interactions of this type primarily in 'bridge-flipped' nitrilehalogen substituted benzylideneanilines (Ojala et al, 2009(Ojala et al, , 2001(Ojala et al, , 1999, where they play a significant role in defining the molecular packing arrangment. Here, we describe the interactions found in a group of 'bridge-flipped' nitrile-halogen substituted phenylhydrazones.…”

Structural systematics and conformational analyses of a 3×3 isomer grid and three chlorinated relatives

“…The single crystal X-ray data (Mo) were collected on an Oxford Diffraction Gemini SUltra diffractometer at 294(1) K:  range from 2-26 (100% data coverage to 25°). 4 Conformational analyses on gas phase and solvation models has enabled comparisons of optimised geometries with solid state molecular structures, highlighting unusual solid state conformations and relations with the aggregation processes. Future research will gg g p finalise the four F/CH 3 benzamide/pyridinecarboxamide series of 3×3 isomer grids, as well as explore related n×m isomer grids by introducing other functional groups/atoms and/or linker backbone using approaches similar to those reported previously.…”

Short C–H⋯F interactions involving the 2,5-difluorobenzene group: understanding the role of fluorine in aggregation and complex C–F/C–H disorder in a 2 × 6 isomer grid

“…The unit cell data are: 10 Of note is that the F 2 -34, 34-F 2 pair also differ from the isomorphous Mmm 13 and NmmM 15 pair that involves amide bridge-flipping. 11 Replacement of two H atoms by two F and vice-versa, resulting in similar crystal structures is unusual but not unexpected and is readily accommodated: the isostericity of H and F is well-known. Future studies may reveal combinations of 3,4-difluoro substituted systems that are isomorphous with F 2 -34 and 34-F 2 .…”