Copper (II) complexes with novel Schiff-based ligands: synthesis, crystal structure, thermal (TGA–DSC/FT-IR), spectroscopic (FT-IR, UV-Vis) and theoretical studies

Abstract

This study aimed to synthesize two novel Schiff-base ligands through the condensation between N-(2-aminoethyl)pyrazoles and 2-hydroxy-1-naphthaldehyde, which are: NaphPz ((E)-1-(((2-(1H-pyrazol-1-yl)ethyl)imino)methyl)naphthalen-2-ol)) and NaphDPz ((E)-1-(((2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)imino)methyl)naphthalen-2-ol). These novel pyrazole-imines were synthesized, characterized and used as copper (II) ion complexing agents. Different synthetic routes have been adapted to obtain the [Cu(NaphPz)Cl], [Cu(NaphDPz)Cl] and [Cu(NaphPz)2] complexes in the solid state, the first two in the crystalline form and the latter as a powder. The minimum metal–ligand stoichiometry for the three complexes was defined by TGA–DSC thermoanalytical data and by single-crystal X-ray diffraction for the crystalline samples which belong to the P21/n space group. The products of the thermal decomposition of the material were also monitored by TGA–DSC/FT-IR in air and N2 atmospheres in order to suggest how thermal decomposition of the organic portion of the complex occurs. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations compared to experimental results (UV-Vis and FT-IR) show a high degree of correlation. From HOMO/LUMO orbitals, the main major charge distributions, responsible for the absorption bands of the complexes, were determined.