Synthesis, Crystal Structure, and Hirshfeld Analysis of a Novel Schiff Base Compound 5-Hydroxy-2-{[(Propan-2-yl)Iminio]Methyl}Phenolate

Abstract— 5-Hydroxy-2-{[(propane-2-yl)iminio]methyl}phenolate with an empirical formula of C₁₀H₁₃NO₂ was synthesized by a reaction between 2,4-dihydroxybenzaldehyde and isopropyl amine in an aqueous ethanolic medium. The Schiff base compound was characterized by elemental analysis, IR spectroscopy, NMR, mass-spectrometry, thermogravimetry (TG), and single-crystal X-ray diffraction (XRD). The compound was crystalized in an orthorhombic crystal system with a space group of Pna2₁. The azomethine functional group (–HC=N–) was confirmed by the band at 1638 cm^–1 in its IR spectrum. The compound is thermally stable from 40-154 °C losing only 0.2% of its weight. The thermogram indicated the absence of hydration or lattice water. The compound exhibits keto-enol tautomerism with a zwitterionic structure. The non-covalent interactions (NCI) were studied by various computational methods such as Hirshfeld surface analysis, NCI plot, and scatter plot (RDG vs sign (λ₂)ρ). The major contributors to the Hirshfeld surface contacts are O⋯/H⋯O (21.5%) and C⋯/H⋯C (25.3%). The non-covalent interactions and the crystal parameters are: a = 10.3839(9) Å, b = 9.9442(8) Å), c = 9.2223(8) Å, α = β = γ = 90°, Z = 4.