Structural and spectroscopic characterization of Zn(II) complexes: A computational perspective on anticorrosion potential of bronze surface

Abstract

The coordination of Zn(II) carboxylates with nitrogen donor ligands significantly influences the physicochemical properties of metal complexes, due to their structural diversity. Herein, we report the synthesis and characterization of Zn(II) heteroleptic complexes with the general formulae [(L1)₂Zn(bipy)] (1), [(L2)₂Zn(bipy)] (2), [(L3)₂Zn(quinoline) (H₂O)] (3), [(L4)₂Zn(quinoline) (H₂O)] (4), and [(L5)₂Zn(quinoline) (H₂O)] (5), where L1–L5 represent benzoic acid or phenyl acetic acid derivatives, and bipy denotes 2,2-bipyridne. All complexes were thoroughly characterized using FTIR, UV–vis, and ¹H/¹³C NMR (for complexes 3–5 only). The structures of 1 and 2 were further confirmed by single-crystal X-ray diffraction. All complexes are mononuclear, incorporating two carboxylate ligands. Complexes 1 and 2 contain one 2,2′-bipyridine ligand, while complexes 3–5 feature a quinoline ligand and a water molecule. Most of the complexes adopt hexacoordinated structures. However, complex 1 is tetra-coordinated, exhibiting a distorted tetrahedral geometry. Various coordination modes are observed, including both monodentate 1, a combination of monodentate and bidentate (3–5), and both bidentate coordination 2. All the complexes were optimized for their HOMO/LUMO energy by using DFTD. The anticorrosion ability of all complexes was evaluated by Monte Carlo (MC) and molecular dynamics (MD) simulations. MC and MD simulations of complexes 1–5 on the bronze (100) surface, along with negative adsorption energies, reveal strong first-layer localization through both chemisorption and physisorption. The degree of adsorption of complexes 1–5 follows the order 3 > 2 > 5 > 4 > 1.