Bridge-Flipped Isomers: Searching for IsomorphousBenzylideneanilines and Phenylhydrazones Reveals Unexpected Structures

Examination of a series of “bridge-flipped” halogen- and nitrile-substituted benzylideneanilines for isomorphism by single-crystal X-ray diffraction has resulted in identification of three non-isomorphous pairs: N-(4-cyanobenzylidine)-2-fluoroaniline (2Fan)/N-(2-fluorobenzylidene)-4-cyanoaniline (2Fbz); N-(4-cyanobenzylidene)-2-chloroaniline (2Clan)/N-(2-chlorobenzylidene)-4-cyanoaniline (2Clbz), and N-(4-cyanobenzylidene)-2-cyanoaniline (2CNan)/N-(2-cyanobenzylidene)-4-cyanoaniline (2CNbz). Their crystal structures are rendered unique by differences in solid-state molecular conformation and intermolecular interactions. The crystal structures of N-(4-cyanobenzylidene)-2-bromoaniline (2Bran) and N-(4-cyanobenzylidene)-2-iodoaniline (2Ian) were determined, but upon attempts to prepare their bridge-flipped isomers the unexpected dianilines 1-(2-bromophenyl)-N,N’-bis(4-cyanophenyl)methanediamine (2Brdian) and 1-(2-iodophenyl)-N,N’-bis(4-cyanophenyl)methanediamine (2Idian) were obtained. The crystal structures...