Three polymorphs of 4-4′-diiodobenzalazine, and 4-chloro-4′- iodo-benz-alazine

Three polymorphs of 4,4′-diiodobenzalazine (systematic name: 4-iodo-benzaldehyde azine), C14H10I2N2, have crystallographically imposed inversion symmetry. 4-Chloro-4′-iodobenzalazine [systematic name: 1-(4-chloro-benzyl-idene)-2-(4-iodo-benzyl-idene)diazane], C14H10ClIN2, has a partially disordered pseudocentrosymmetric packing and is not isostructural with any of the polymorphs of 4,4′-diiodo-benzalazine. All structures pack utilizing halogen-halogen inter-actions; some also have weak π (benzene ring) inter-actions. A comparison with previously published methyl-phenyl-ketalazines (which differ by substitution of methyl for H at the azine C atoms) shows a fundamentally different geometry for these two classes, namely planar for the alazines and twisted for the ketalazines. Density functional theory calculations confirm that the difference is fundamental and not an artifact of packing forces.