Synthesis, characterization, Hirshfeld surface analysis and DFT studies of novel hydralazine-based compounds

Three new hydralazine-based compounds (1–3) were synthesized and characterized by spectroscopic techniques (FT-IR, UV-Vis, NMR, HRMS). The crystal structures of compounds 1 and 2 were determined by single-crystal XRD. The compounds exhibit diverse tautomeric forms and distinct supramolecular organizations governed by hydrogen bonding and π–π stacking interactions. Structural studies in both compounds 1 and 2 revealed that both phthalazine and phenyl rings are nearly coplanar, promoting extended conjugation and rigidity. Hirshfeld surface and energy framework analyses indicate that H···H, N···H, O···H, and Cl···H contacts are the dominant contributors to crystal packing stability. DFT calculations generated optimized geometries and electronic parameters consistent with experimental results. Frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) analyses revealed that compound 1 possesses the highest HOMO energy and dipole moment, indicating its higher donor ability and polar character. These combined experimental and theoretical investigations offer valuable insights into the structure–property relationships of hydralazine-derived compounds.