Pairs of molecules we define as “bridge-flipped isomers” differ structurally only in the orientation of a bridge of atoms connecting two major molecular moieties. Examples occur among the benzylideneanilines, where the isomerism is Ar1-CH=N-Ar2 vs. Ar1-N=CH-Ar2, and among the phenylhydrazones, where the isomerism is Ar1-NH-N=CH-Ar2 vs. Ar1-CH=N-NH-Ar2 (Ar = aryl). We use single-crystal X-ray diffraction to determine whether bridge-flipped isomers are isomorphous, crystallizing into the same molecular packing arrangement. Isomorphous pairs may form interesting solid solutions; non-isomorphous pairs may serve as seed crystals for each other and thereby induce formation of new isomorphous crystalline forms. Assuming that the occurrence of similar molecular packing motifs in both members of a bridge-flipped isomeric pair might encourage their isomorphism, and to promote formation of motifs defined by nitrogen…iodine Lewis acid-base contacts, we have begun the synthesis and crystallization of a 3-pyridine-derived system of benzylideneanilines bearing iodine substituents. The anticipated shared motif would be zigzag molecular chains defined by nitrogen...iodine contacts. Concurrently we have begun the synthesis and crystallization of diimines based on hydrazine and have now determined the crystal structure of one of these compounds, the bis(2,5-dimethoxyphenyl) derivative. Crystal structures of this and other hydrazine-based bis-benzylideneanilines will be compared to those of their bridge-flipped analogues, the corresponding bis-benzylideneanilines based on glyoxal. Samples are now in preparation for X-ray crystal structure analysis.

Toward isomorphous “bridge-flipped” isomers:  Investigations of 3-pyridyl and hydrazine-based systems and the crystal structure of a hydrazine-based diimine

2019 Spring National Meeting

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