Structural and Electronic Features of a Julolidine Schiff Base Revealed by X- ray Crystallography and DFT Calculations
Abstract
Abstract A new hydroxy substituted pyridoquinoline Schiff base, 9-[(4-hydroxy-phenylimino)-methyl]-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol was synthesized by condensation of 8-hydroxy-9-formyl-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinoline with p-aminophenol in refluxing methanolic solution. The 1H NMR, UV–Visible spectroscopy, single-crystal X-ray diffraction, Hirshfeld surface analysis and density functional theory (DFT) calculations led to the establishment of the molecular structure. Intramolecular O–H···N hydrogen bond stabilises the nearly planar conformation in the molecule, the solid-state being in the enol–imine tautomer, as revealed by the single-crystal X-ray analysis. The crystal packing is directed by intermolecular hydrogen bonding, weak C–H···π and π–π interactions, which results in the construction of a strong supramolecular network. Hirshfeld surface analysis and two-dimensional fingerprint plots revealed that the most abundant H···H (58.1%) contacts follow, followed by the C···H/H···C (23.2%) and O···H/H···O (12.7%) contacts, which reveals the crucial role that hydrogen bonding and van der Waals forces play in the stabilization of the crystal. The enol and keto tautomers showed a characteristic π→π* transition in the 220–230 nm region and an n→π*/intramolecular charge-transfer band in the 340–370 nm region, which suggests that both have a high degree of π-conjugation and the delocalization of electronic energy is very efficient.…
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