title: Isostructuralism among bridge-flipped' isomeric benzylideneanilines and phenylhydrazones.
abstract: Bridge-flipped' isomers may be defined as pairs of molecules related by a reversal of a bridge of atoms connecting two major parts of the individual molecules. This kind of isomerism is commonly found among benzylideneanilines and phenylhydrazones. Isostructural pairs might be suitable for co-crystallization and are thus useful in the preparation of new solid materials. Although most of the examples of bridge-flipped isomeric benzylideneanilines and phenylhydrazones in the crystallographic literature are not isostructural, a small number of isostructural pairs have been reported by previous workers. This paper describes the molecular and crystal structures of four pairs of bridge-flipped isomers: two isostructural phenylhydrazones, (E)-2-bromobenzaldehyde 4-cyanophenylhydrazone (I) and (E)-4-cyanobenzaldehyde 2-bromophenylhydrazone (II); two pairs of isostructural benzylideneanilines, N-(2-trifluoromethylbenzylidene)-2-methylaniline (III) and N-(2-methylbenzylidene)-2-trifluoromethylaniline (IV), and N-(2-bromobenzylidene)-2-methylaniline (V) and N-(2-methylbenzylidene)-2-bromoaniline (VI); and a pair of benzylideneanilines with closely similar unit-cell dimensions but different packing arrangements, N-(4-methylbenzylidene)-4-cyanoaniline (VII) and N-(4-cyanobenzylidene)-4-methylaniline (VIII). The structure of (V) is disordered. The packing arrangement of (VIII) resembles that of the chloro-/methyl-substituted benzylideneanilines MBZCLA/MBZCLB [N-(4-methylbenzylidene)-4-chloroaniline and N-(4-chlorobenzylidene)-4-methylaniline]. Although intermolecular hydrogen bonding plays a part in the isostructuralism of the two phenylhydrazones, the other examples of isostructuralism occur in the absence of similar, relatively strong intermolecular interactions.
authors.affiliation: Department of Chemistry, University of St Thomas, St Paul, Minnesota 55105, USA. whojala@stthomas.edu
authors.forename: William H
authors.initials: WH
authors.lastname: Ojala
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Smieja
authors.forename: Jill M
authors.initials: JM
authors.lastname: Spude
authors.forename: Trina M
authors.initials: TM
authors.lastname: Arola
authors.forename: Marika K
authors.initials: MK
authors.lastname: Kuspa
authors.forename: Nell
authors.initials: N
authors.lastname: Herrera
authors.forename: Charles R
authors.initials: CR
authors.lastname: Ojala