Nickel(II)-PPh₃ complexes of substituted benzophenone thiosemicarbazones: Electrochemistry, structural analysis, and antioxidant properties

Abstract

New mixed ligand complexes of nickel(II) were synthesized by using dibasic H/5-bromo-/5-chloro-/4-hydroxy-2-hydroxybenzophenone-thiosemicarbazones (L^1–4H₂) and [Ni(PPh₃)₂Cl₂]. The ligands and complexes were characterized by cyclic voltammetry, infrared, ¹H and ³¹P NMR spectroscopy techniques. Crystallographic analyses of the 5-bromo-substituted (2) and 5-chloro-substituted (3) complexes as representatives were performed and so confirmed the ONS chelate structure and presence of PPh₃ as co-ligand in the complexes. To reveal the antioxidant properties of the compounds, TEAC values (by CUPRAC method) were determined along with free radical-scavenging activity (by DPPH method). The compounds bearing 4-hydroxy substituent, L⁴H₂ and complex 4 were the most effective compounds. The relationship between structure and antioxidant capacity in the context of benzophenone substituents and nickel(II) center was evaluated. Electrochemical results revealed that all complexes displayed metal-centered and ligand-centered redox processes. The antioxidant capacities of complexes were well correlated to electrochemical parameters.

Graphical Abstract

Keywords:

• Benzophenone
• thiosemicarbazone
• nickel(II)
• triphenylphosphine
• antioxidant capacity
• electrochemistry

Acknowledgements

I dedicate this paper to Dr. Bahri ÜLKÜSEVEN and Dr. Tülay BAL-DEMİRCİ, the mentors of my research career. I also sincerely thank to Dr. Sinem ORTABOY for her kind help. I would like to express our sincere gratitude towards the Crystallography Laboratory Unit, Ondokuz Mayıs University, for the X-ray data collection, which was supported by the University Research Fund (Project No: PYO.FEN.1906.19.001).

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This research was supported by BAP (The Scientific Research Projects Coordination Unit of Istanbul University – Cerrahpasa (BYP-2018-27646))