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.