Variations in the intermolecular interactions in (E) benzaldehyde 7-chloro-1-methyl- 4H-quinolinyl-4-ylidene-hydrazone and seven halo derivatives

Abstract

Abstract Eight crystal structures are reported here: substituted (E) benzaldehyde 7-chloro-1-methyl-4H-quinolinyl-4-ylidene-hydrazones, 1, [substituted benzaldehyde: XYC6H4CHO: X,Y=H,H; 2-F,H; 3-F,H; 4-F,H; 3-Cl,H; 4-Cl,H; 2-Br,H and 2,3-Cl2]. None of the molecules, 1, are overall planar: angles between the phenyl and and quinolinyl rings vary from <5°, for (1:X,Y=3-F,H; 4-F,H; 3-Cl,H and 2,3-Cl2) to 15–16° for (1: X,Y=H,H and 4-Cl,H). The supramolecular arrangements in the parent compound (1: X=Y=H) are generated solely from C–Z···π (Z=H and Cl) interactions, while the supramolecular arrangements for each of the halo derivatives arise from combinations of π···π and some of C–Z···π (Z=H, F, Cl) and C–H···Z (Z=N, F, Cl) intermolecular interactions: in each case different assemblies result. While there are possibilities for π(quin)···π(quin), π(quin)···π(phen) and π(phen)···π(phen) interactions [quin and phen refer to the quinolinyl and phenyl moieties], only compounds (1: X,Y=2,3-Cl2) and (1: X,Y=4-Cl,H) exhibit all three, (1: X,Y=2-Br,H) just π(quin)···π(quin) of the three, and in the others two of the three. All the halo derivatives exhibit π(quin)···π(quin) interactions. It is argued that steric hindrance between molecules, generated by the halo substituents, prevents the halo derivatives from adopting the packing arrangements of the parent compound, (1: X,Y=H,H). As there appears to be no reason, steric or otherwise, why compound (1: X,Y=H,H) cannot utiilize π···π interactions, it is apparent that the packing of molecules via the C–Y···π interactions is the most stable.