Synthesis, crystal structure, Hirshfeld surface analysis and halogen-involving interactions in a...

The title Br/Cl-substituted Schiff base, C₁₅H₁₂BrCl₂NO₂, was synthesized via condensation of 2,4-dichloroaniline with 3-bromo-4,5-dimethoxybenzaldehyde under mild acidic conditions. Its molecular and crystal structures were determined by single-crystal X-ray diffraction (monoclinic space group C2/c, Z = 8). Structurally, the molecule adopts a twisted conformation, with an angle of approximately 41.6 (4)° between the planes of the 3-bromo-4,5-dimethoxyphenyl and 2,4-dichlorophenyl moieties, a value significantly greater than those reported for related halogen-substituted Schiff bases in the literature, indicating a substantial disruption of the π-conjugated system across the azomethine bridge. The E configuration is confirmed, with a C=N bond length of 1.281 (3) Å, consistent with partial double-bond character resulting from the opposing electronic effects of the methoxy donors and the halogen withdrawing groups. In the crystal, intermolecular C-H...Cl and C-H...Br contacts of 2.96 and 3.04 Å, respectively, compared to the van der Waals sums of 2.95 and 3.05 Å, link molecules into supramolecular chains along the a axis, demonstrating that the twisted molecular geometry, imposed by halogen substitution, directly governs the three-dimensional crystal packing. Hirshfeld surface analysis confirms that halogen-involving interactions collectively account for 32% of the total surface area (Cl...H/H...Cl = 20% and Br...H/H...Br = 12%), ranking them among the most significant contributors to supramolecular stabilization alongside H...H (27%), C...H/H...C (12.1%) and O...H/H...O (5.2%) contacts. Finally, energy framework calculations indicate that dispersion interactions dominate the stabilization of the crystal structure, thus highlighting the key role of weak van der Waals forces in the supramolecular assembly.