Copper(I/II) and Palladium(II) Complexes Containing Carbothioamide and Triphenylphosphine Ligands: Synthesis, Characterization, and Theoretical Studies

Abstract

A carbothioamide ligand, 4,5-dihydro-5-(4-methoxyphenyl)-3-phenylpyrazole-1-carbothioamide, [C₁₇H₁₇N₃OS], has been synthesized from the condensation of 4-methoxychalcone with thiosemicarbazide. The carbothioamide (L) ligand and triphenylphosphine (Ph³P) as co-ligand, was coordinated with Cu(I), Cu(II), and Pd(II) metal ions to synthesis the corresponding complexes: [CuCl₂(L)] 1, [CuCl(L)(Ph³P)] 2, [PdCl₂(L)] 3, and [PdCl(L)(Ph₃P)]Cl 4. The ligand and all complexes were collected in solid form after the reactions and characterized by magnetic susceptibility, elemental analysis, molar conductivity, FT-IR, UV-Vis, and ¹H, ¹³C, ³¹P-NMR techniques. The molar conductance values in DMSO (5.8–16.3 Ω^–1 cm² mol^–1) confirmed all the complexes to be non-electrolytic except for the Pd(II) complex 4 (32.6 Ω^–1cm² mol^–1) that behaves as a 1:1 electrolyte. According to spectroscopic evidence, the carbothioamide ligand behaves as an N, S donor and chelating agent. Magnetic susceptibility measurements combined with electronic spectral data suggest that the Cu(II) and Pd(II) complexes have square planar geometry, whereas the Cu(I) complex 2 has a tetrahedral geometry. Elemental analysis and ¹H-NMR spectroscopy confirmed the mononuclear structure of all complexes. DFT calculations showed that the synthesized complexes 1, 3, and 4 exhibit higher thermodynamic stability than the free ligand (L), with ΔE values of 1.4695, 2.1116 eV, 1.9076 eV, and 1.2980 eV, respectively. In contrast, complex 2 has ΔE = 0.5385 eV, indicating lower thermodynamic stability. Among the complexes, complex 2 (S = 3.7140 eV) exhibited the highest softness, and all complexes were observed to be softer than the triphenylphosphine ligand. According to the results, electron transitions are easier in certain complexes than in their ligands, which suggests that the prepared complexes could be used in the photocell in future studies.