Synthesis, electrochemical and structural characterization of novel azacrown ether containing macrocyclic redox-active vic-dioxime ligand and its mononuclear transition metal complexes: Application of DEPT, HSQC, HMBC-NMR and cyclic voltammetry

This paper presents a new azacrown containing vic-dioxime; anti-N-(4-aminophenyl)aza-15-crown-5-glyoxime (LH2), and its mononuclear nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) complexes. The azacrown moieties appended at the periphery of the oxime provide solubility for the vic-dioxime ligand and complexes in common organic solvents. The mononuclear M(LH)2 (M = Ni and Cu), M(LH)2(H2O)2 (M = Co) and [M(LH)(H2O)(Cl)] (M = Cd and Zn) complexes have been obtained with the metal:ligand ratios of 1:2 and 1:1. The structure of the ligand is confirmed by elemental analysis, Fourier transform infrared (FT-IR), ultraviolet–visible (UV–Vis), mass spectrometry (MS), one-dimensional (1D) 1H, 13C NMR, distortionless enhancement by polarization transfer (DEPT) and two-dimensional (2D) heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) techniques. The structures of the complexes are confirmed by elemental analyses, MS, UV–Vis, FT-IR and 1H, 13C NMR techniques. Redox behaviors of the ligand and its complexes have been investigated by cyclic voltammetry at the glassy carbon electrode in 0.1 M TBATFB in DMSO. The antibacterial activity was studied against Staphylococcus aureus ATCC 29213, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922, Pseudomonasaeruginosa ATCC 27853. The antimicrobial test results indicate that all the complexes have low levels of antibacterial activity against both Gram negative and Gram positive bacterial species. -

Keywords: vic-Dioxime; Azacrown ether; Macrocyclic ligand; Metal complexes; Cyclic voltammetry; Antimicrobial activity