Homo-dinuclear VO2+ and Ni2+ dihydrazone complexes: Synthesis, characterization, catalytic activity and CO2-corrosion inhibition under sustainable conditions

Abstract

VO2+ and Ni2+ complexes (VOPHL and NiPHL) were prepared by complexation of terephthaloyl salicylidene dihydrazone (H2PHL) with VO2+ or Ni2+ ions. The chemical structures were estimated by various spectroscopic methods. Their sustainable corrosion inhibition on mild steel in NaCl solutions saturated with CO2 was investigated using potentiodynamic polarization (PDP), open circuit potential and electrochemical impedance spectroscopy (EIS) methods. H2PHL, NiPHL and VOPHL showed maximum capacity within 89.57, 97.25 and 98.22%, respectively. The PDP study refers to that they could act as mixed-type inhibitors i.e. retarded both cathodic and anodic reactions. Metal complexes displayed better inhibition than their coordinated ligand. H2PHL and its M-complexes adsorbed on C-steel surface via chemical adsorption with obeying the Langmuir model. The post-exposure investigation, for the inhibited and uninhibited C-steel surface, was elucidated using SEM /EDS. The homogeneous catalytic behavior of NiPHL and VOPHL was studied in the (ep)oxidation of unsaturated cycloalkene (1,2-cyclohexene) and Suzuki-Miyaura cross-coupling. VOPHL shows better catalytic potential in (ep)oxidation processes. NiPHL has higher catalytic efficiency towards cross-couplings. The aqueous hydrolysis of epoxy selective product could be reduced in low temperature of the (ep)oxidation processes. DFT studies were performed on H2PHL, NiPHL and VOPHL. Electronic representatives ELUMO, EHOMO, energy gap (ΔE), hardness, softness and electronegativity were computed. Theoretical values are in good accordance with corrosive and catalytic experimental results.