Crystal structures and Hirshfeld surface analysis of four 1,4-bis(methoxyphenyl)-2,3-diazabuta-1,3-dienes: comparisons of the intermolecular interactions in related compounds

The crystal structures of four azines, namely 1-3-bis(4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 1, 1,3-bis(2,3-dimethoxyphenyl)-2,3-diaza-1,4-butadiene, 2, 1,3-bis(2-hydroxy-3-methoxyphenyl)-2,3-diaza-1,4-butadiene, 3, and 1,3-bis(2-hydroxy-4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 4, are reported. Molecules of 3 and 4, and both independent molecules of 2, Mol A and Mol B, possess inversion centers. The central C=N-N=C units in each molecule is planar with an (E,E) conformation. The intermolecular interactions found in the four compounds are C-H center dot center dot center dot O, C--H---N, C--H---pi and pi---pi interactions. However, there is no consistent set of intermolecular interactions for the four compounds. Compound, 1, has a twodimensional undulating sheet structure, generated from C-H center dot center dot center dot O and C-H center dot center dot center dot N intermolecular hydrogen bonds. The only recognized intermolecular interaction in 2 is a C-H center dot center dot center dot O hydrogen bond, which results in a zig-zag chain of alternating molecules, Mol A and Mol B. While 3 forms a puckered sheet of molecules, solely via C-H center dot center dot center dot pi interactions, its isomeric compound, 4, has a more elaborate three-dimensional structure generated from a combination of C-H center dot center dot center dot O hydrogen bonds, C-H center dot center dot center dot pi and pi center dot center dot center dot pi interactions. The findings in this study, based on both PLATON and Hirshfeld approaches, for the four representative compounds match well the reported structural findings in the literature of related compounds, which are based solely on geometric parameters.