Synthesis and characterization of N,N′-bis(2-thienylmethylene)-1,X-diaminobenzene isomers (X = 2, 3, 4) and their metal complexes

The synthesis of N,N′-bis(2-thienylmethylene)-1,2-diaminobenzene, N,N′-bis(2-thienylmethylene)-1,3-diaminobenzene, and N,N′-bis(2-thienylmethylene)-1,4-diaminobenzene, three isomers with the molecular formula of (C₁₆H₁₂N₂S₂) and their metal complexation with Co(ii), Fe(iii), and Ni(ii) is reported in this study. The formation of the ligands and their metal complexes, along with their physicochemical behaviors, are confirmed and characterized using electrochemical and spectroscopic techniques. The coordination chemistry and stoichiometry of the ligand-metal complexes are investigated using UV-vis absorption spectral titration, which reveals that the ligand-to-metal ratio varies from 3 : 1 to 4 : 1 in different cases. The calculated binding constants based on these spectroscopic data, ranging between 10³ M⁻¹ and 10⁸ M⁻¹, indicate the isomers' high affinity for the metal ions. Experimental data show that the nitrogen atoms from the azomethine linkage play an important role in coordinating with the metal ions. This observation supports findings reported in the literature for some studied Schiff base ligands.