N,N′-dipyridoxyl Schiff bases: Synthesis, experimental and theoretical characterization

Three N,N′-dipyridoxyl Schiff bases (L1, L2 and L3) have been newly synthesized and characterized by IR, 1H NMR, mass spectrometry and elemental analysis. Their optimized geometries together with the theoretical assignment of the vibrational frequencies and the 1H NMR chemical shifts of them have been computed by using density functional theory (DFT) method. In the optimized structures of the Schiff bases, two pyridine rings are not in a same plane; however the substitutions are essentially in the same plane with the pyridine rings. Also, the benzene ring(s) in the bridge region is (are) not in the same plane with the pyridine rings and azomethine moieties. In all the species, engagement in intramolecular-hydrogen bonds causes to weakness of the phenolic O–H bonds. Consistency between the theoretical results and experimental evidence confirms suitability of the optimized geometries for the synthesized Schiff bases.

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► Synthesis of some dipyridoxal Schiff-base ligands.
► Theoretical assignment of their IR and NMR spectra.
► Optimized geometries of the ligands are not planar.
► Engagement in intramolecular H-bonding affects the 1H NMR chemical shifts of the phenolic hydrogens.