Three Polymorphs of 4,4'-Diiodobenzalazine; 4-Chloro-4'-iodobenzalazine

Ojala, C. R.; Ojala, W. H.; Britton, D.; Cramer, C. J.
Acta Cryst. C 2007, C63, o518.

Three polymorphs of 4,4'-diiodobenzalazine (systematic name: 4-iodobenzaldehyde azine), C₁₄H₁₀I₂N₂, have crystallographically imposed inversion symmetry. 4-Chloro-4'-iodobenzalazine [systematic name: 1-(4-chlorobenzylidene)-2-(4-iodobenzylidene)diazane], C₁₄H₁₀ClIN₂, has a partially disordered pseudocentrosymmetric packing and is not isostructural with any of the polymorphs of 4,4'-diiodobenzalazine. All structures pack utilizing halogen-halogen interactions; some also have weak π (benzene ring) interactions. A comparison with previously published methylphenylketalazines (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.

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