Geometrical structures, thermal properties and antimicrobial activity studies of azodye complexes

A novel series of metal complexes with 4-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-3-aminophenol ligand (HL) are prepared and characterized by elemental analyses, IR, UV–Visible spectra, ¹H NMR spectra, mass spectra, X-ray diffraction analysis, conductivity measurements and magnetic susceptibility measurements as well as thermal analysis. The IR spectrum revealed that the ligand (HL) coordinates as monobasic tridentate manner with ONO donor sites of nitrogen atom of azo group (

N

N), oxygen atom of the deprotonated phenolic

OH group and exocyclic carbonyl oxygen atom forming a five/six-membered chelate structures. The ¹H NMR spectra data indicated that the phenolic proton is also displaced during complexation. From the magnetic and spectral studies, it was obvious that the geometrical structures of these complexes are octahedral. The molecular structures of the ligand (HL) and its metal complexes are optimized theoretically and the quantum chemical parameters are calculated. The XRD patterns of the ligand (HL) and complex (3) are a mixture of crystalline and amorphous phases. The activation thermodynamic parameters, such as activation energy (E_a), enthalpy (ΔH^⁎), entropy (ΔS^⁎), and Gibbs free energy change of the decomposition (ΔG^⁎) are calculated using Coats–Redfern and Horowitz–Metzger methods. The ligand (HL) and its metal complexes are screened for their antimicrobial activity against, four bacteria (two Gram positive, i.e. Bacillus subtilis, Streptococcus pneumoniae, and two Gram negative, i.e. Escherichia coli and Pseudomonas aeruginosa) and two fungi species (Aspergillus fumigatus and Candida albicans). The obtained data implies that all the complexes have high antimicrobial activities toward B. subtilis, S. pneumoniae, E. coli and A. fumigatus than the ligand (HL). In addition to that, complexes (1), (3) and (5) showed antifungal effect against C. albicans.