Synthesis and structures of divalent Co, Ni, Zn and Cd complexes of mixed dichalcogen and dipnictogen ligands with corrosion inhibition properties: experimental and computational studies

Tunde L Yusuf; Taiwo W Quadri; Gideon F Tolufashe; Lukman O Olasunkanmi; Eno E Ebenso; Werner E van Zyl

doi:10.1039/d0ra07770d

Synthesis and structures of divalent Co, Ni, Zn and Cd complexes of mixed dichalcogen and dipnictogen ligands with corrosion inhibition properties: experimental and computational studies

RSC Adv. 2020 Nov 18;10(69):41967-41982. doi: 10.1039/d0ra07770d. eCollection 2020 Nov 17.

Authors

Tunde L Yusuf¹, Taiwo W Quadri², Gideon F Tolufashe³, Lukman O Olasunkanmi^{2

4}, Eno E Ebenso^{2

5}, Werner E van Zyl¹

Affiliations

¹ School of Chemistry and Physics, University of KwaZulu-Natal Westville Campus, Chiltern Hills, Private Bag X54001 Durban 4000 South Africa vanzylw@ukzn.ac.za +27 31 260 3188.
² Department of Chemistry, School of Physical and Chemical Sciences, Materials Science Innovation and Modelling (MaSIM) Research Focus Area, Faculty of Natural and Agricultural Sciences, North-West University (Mafikeng Campus) Private Bag X2046 Mmabatho 2735 South Africa.
³ Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto 4169-007 Porto Portugal.
⁴ Department of Chemistry, Faculty of Science, Obafemi Awolowo University Ile-Ife 220005 Nigeria.
⁵ Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa Johannesburg South Africa.

Abstract

The structural and corrosion inhibition properties of four different transition-metal complexes of heteroleptic S-donor atom dithiophosphonate and N-donor atom phenanthroline ligands are reported. Full structural characterization of the Co, Ni, Zn and Cd complexes was achieved with the aid of single-crystal X-ray crystallography. Structural elucidation revealed the formation of a 4-coordinate Zn(ii) complex, and 6-coordinate Ni(ii) and Cd(ii), as well as a novel dithiophosphonato Co(ii) complex. The ability of the complexes with this ligand type to act as inhibitors of mild steel corrosion in 1 M HCl solution is reported for the first time. Corrosion inhibition potentials of the complexes were assessed using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and density functional theory (DFT). The open circuit potential (OCP) time profile showed the system achieved a steady-state potential before the first 600 s after submerging the working electrode in the corrosive medium. The studied metal complexes are good inhibitors of mild steel corrosion in 1 M HCl and were found to retard the corrosion rate by forming an adsorbed pseudocapacitive film on the steel surface. The order of inhibition efficiencies was in the order Ni (94.14%) > Cd (92.28%) > Zn (91.14%) > Co (72.53%).