Competing inter-molecular inter-actions in some bridge-flipped isomeric phenylhydrazones

Abstract

To examine the roles of competing inter-molecular inter-actions in differentiating the mol-ecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile-halogen substituted phenylhydrazones and two nitro-halogen substituted phenylhydrazones have been determined and are described here: (E)-4-cyanobenzaldehyde 4-chloro-phenyl-hydrazone, C14H10ClN3, (Ia); (E)-4-cyanobenzaldehyde 4-bromo-phenyl-hydra-zone, C14H 10BrN3, (Ib); (E)-4-cyanobenzaldehyde 4-iodo-phenyl- hydrazone, C14H10IN3, (Ic); (E)-4-bromo-benzaldehyde 4-cyanophenyl-hydrazone, C14H 10BrN3, (IIb); (E)-4-iodo-benzaldehyde 4-cyanophenyl-hydrazone, C14H10IN3, (IIc); (E)-4-chloro-benzaldehyde 4-nitro-phenyl-hydrazone, C13H 10ClN3O2, (III); and (E)-4-nitro-benzaldehyde 4-chloro-phenyl-hydrazone, C13H10ClN3O 2, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the bridge-flipped isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile-halogen structures (Ia)-(Ic) and (IIb)-(IIc), only the bridge N - H group and not the bridge C - H group acts as a hydrogen-bond donor to the nitrile group, but in the nitro-halogen structures (III) (with Z' = 2) and (IV), both the bridge N - H group and the bridge C - H group inter-act with the nitro group as hydrogen-bond donors, albeit via different motifs. The occurrence here of the bridge C - H contact with a hydrogen-bond acceptor suggests the possibility that other pairs of bridge-flipped isomeric phenyl-hydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N - H group within the bridge. © 2012 International Union of Crystallography.