Abstract
Examination of a series of "bridge-flipped" halogen- and nitrile-substituted benzylideneanilines for isomorphism by single-crystal X-ray diffraction has resulted in the 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 (2ldian) were obtained. The crystal structures of 2Brdian and 2Idian were found to be isomorphous, as were the crystal structures of the three pairs 2Clan/2Bran, 2Ian/2CH(3) an (N-(4-cyanobenzylidene)-2-methylaniline), and 2CNan/XOXLOM (N-(4-methylbenzylidene)-2-cyanoaniline). Isomorphism involving iodine/methyl and nitrile/methyl exchanges is rare in the Cambridge Structural Database (CSD). The unexpected product meso-(E,E)-1,1'-[1,2-bis(4-methylphenyl)ethane-1,2-diyll-bis[(2-trifluoromethyl)phenyldiazene] (2CF(3)azo) was obtained in an attempt to prepare the phenylhydrazone, and its crystal structure is reported here. Only one other example of this type of compound currently appears in the CSD. Examples of isomorphous bridge-flipped isomers among benzylideneanilines and phenylhydrazones remain rare in spite of their conformational flexibility and steric similarity.