Pyridazine-based Schiff base ligands with N4OxS2 (x = 2, 4) donor set atoms: Synthesis,characterization, spectral studies and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

Six pyridazine-based Schiff base ligands, H₂Lⁿ (n = 1–5) and H₄L, with N₄O₂S₂ and N₄O₄S₂ donor set atoms, respectively, were prepared by condensation reaction of 3,6-bis-((2-aminoethyl)thio)pyridazine with various salicyladehyde derivatives in ethanol and under solvent-free polyphosphate ester catalyzed conditions. The acid–base properties of H₂L² and H₂L³ in DMSO/water (1:1) solution have been studied by spectrophotometric method at 25 °C. Optimized geometries of all compounds were also obtained at the B3LYP level of theory. Additionally, the ¹³C chemical shielding of gas phase H₂L¹ and H₂L² were studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The 6-311++G* basis set was utilized for all of the atoms.