Copper(I) and zinc(II) complexes containing 4-methoxybenz- aldehyde thiosemi- carbazone and triphenylphosphine ligands, synthesis, characterization, and theoretical studies

A new thioamide ligand, 4-methoxybenzaldehyde thiosemicarbazone (L), containing sulfur, nitrogen, and oxygen atoms, was synthesized via condensation of 4-methoxybenzaldehyde with thiosemicarbazide. New tetrahedral copper(I) and zinc(II) complexes of the prepared ligand and triphenylphosphine (Ph3P) as a co-ligand have been synthesized. The ligand and its complexes were characterized by magnetic susceptibility, elemental analysis, molar conductivity, FT-IR, UV-Vis, and 1H, 13C, 31P-NMR techniques. The FT-IR spectra indicated that the (L) ligand coordinates with the metal ions through sulfur and nitrogen atoms, forming a five-membered chelate ring. Elemental analysis and 1H-NMR spectroscopy confirmed the mononuclear structure of complexes 2, 3, and 4, while complex 1 exhibited a dinuclear configuration. DFT calculations indicated that the synthesized complexes are less thermodynamically stable than the free ligands, with ΔE values of 2.6776 eV, 2.9699 eV, 2.8912 eV, and 0.4996 eV for complexes 1, 2, 3, and 4, respectively. Among the complexes, complex 4 (S = 4.0032 eV) exhibited the highest softness, and all complexes were found to be softer compared to the free ligand. In this study, the results suggest that electron transitions in complexes are easier than in free ligands, which suggest their potential use in photocell technologies in the future. KEY WORDS: Thioamide, Cu(I) complexes, Zn(II) complexes, NBO analysis, DFT calculations Bull. Chem. Soc. Ethiop. 2025, 39(7), 1301-1316. DOI: https://dx.doi.org/10.4314/bcse.v39i7.6