Structural Investigation and Hirshfeld Surface Analysis of Two [ONO]-Type Schiff Bases

Two novel [ONO]-type tridentate Schiff base compounds namely (E)-2-(((2-hydroxyphenyl)imino) methyl)-4,5-dimethoxyphenol, C₁₅H₁₅NO₄ (1), and (E)-2-(((5-chloro-2-hydroxyphenyl)imino)methyl)-4,5-dimethoxyphenol, C₁₅H₁₄ClNO₄ (2) were synthesized. These compounds were characterized using various spectroscopic techniques, including single crystal X-ray diffraction (XRD), infrared (IR), proton nuclear magnetic resonance (¹H NMR), carbon-13 nuclear magnetic resonance (¹³C NMR), and UV-Vis spectroscopy. The X-ray crystallographic analysis revealed that both compounds 1 and 2 contain two independent molecules within the asymmetric unit. Compound 1 crystallizes in the orthorhombic system with the Pna2₁ space group, while compound 2 crystallizes in the monoclinic system with the P2₁/c space group. An important feature observed in the crystal structure of compound 1 is the presence of O–H···N and O–H⋯O hydrogen bonds. In compound 2, the hydrogen bonding interactions involve C–H⋯O, O–H⋯O and O–H⋯N. Additionally, both compounds exhibit C–H⋯π interactions. To further understand the bonding interactions in compounds 1 and 2, Hirshfeld surface analyses and 2D fingerprint graphs were performed. The results indicate that the Hirshfeld surfaces are predominantly influenced by H⋯H, O⋯H, and C⋯H contacts.