Copper(II) and nickel(II) complexes derived from a carbothioamide-5-pyrazolone ligand: synthesis, characterization, crystal structures, electrochemical, potentiometric and DNA-binding studies

Abstract

The synthesis of a 5-pyrazolone derivative (H₂L) bearing a carbothioamide group at N₁, N-ethyl-4-(2-hydroxyethyl)-3-methyl-5-oxo-2,5-dihydro-1H-pyrazole-1-carbothioamide, using a Keggin catalyst (H₄SiW₁₂O₁₄·nH₂O), is described. Complexes of copper(II) and nickel(II) have been prepared with this potential ligand and studied by potentiometry. Processing the pH-metric titrations revealed remarkable chelation ability of the ligand and high stability constants for the complexes. The complexes have been characterized by IR, UV/visible, electrochemistry, magnetic measurements, Electron Paramagnetic Resonance (EPR) and single-crystal X-ray diffraction. The structures are [Cu(HL)₂H₂O]·2H₂O and [Ni(HL)₂H₂O]·2H₂O, where the metal is five coordinate in an almost perfect trigonal bipyramidal geometry (D_3h). The pyrazolone derivative (H₂L) is a NS bidentate negative ligand, which coordinates to the metal through sulfur and amine nitrogen of the pyrazolone ring. The electronic results and the EPR of the complexes have been carefully studied in this (D_3h) crystal field with a special emphasis on the energy levels. DNA-binding experiments have been conducted by UV spectroscopy and electrochemistry. The results reveal an interaction between the complexes and DNA and suggest an intercalative binding mode. UV titrations allowed determination of the binding constants K_b and revealed that the nickel(II) complex binds more strongly.

Keywords:

• Keggin catalyst
• Pyrazolone
• Copper(II)
• Nickel(II)
• Potentiometry
• X-ray structure
• Trigonal bipyramid
• Electrochemistry
• DNA

Acknowledgements

We gratefully acknowledge the Department of Inorganic Chemistry of the University Rey Juan Carlos (Spain) for the FS-DNA and the electrochemical measurements. We would like to thank Pr. Santiago Gomez for his advice and his help in the DNA-interaction study, and Pr. Isabel Del Hierro for her help in the electrochemical part of our work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the CNRS (Centre National de la Recherche Scientifique); Brest University; French “Ministère de la Recherche and Ministère des Affaires Etrangères et Européennes”; PHC Maghreb [grant number 30255ZJ].