Geometrical structures, thermal stability and antimicrobial activity of Schiff base supramolecular and its metal complexes

The 1:1 condensation of 4-amino-1-phenyl-2,3-dimethylpyrazoline-5-one and 8-hydroxy-7-formylquinoline under template condition to obtain the Schiff base ligand 4-{(8-hydroxyquinoline-7-yl)methyleneamino}-1,2-dihydro-1,5-dimethyl-2-phenylpyra-zol-3-one (HL) with NO₂ donor set. Reaction of the ligand with metal salts gives a series of novel complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, ¹H and ¹³C NMR, electronic, ESR, X-ray diffraction and mass spectral, conductivity and magnetic susceptibility measurements as well as thermal analyses. The analytical and spectroscopic tools showed that the complexes can be formulated as: [Cu(L)₂] (1), [CuLX] nH₂O, where X = OAc, n = 2 (2); ONO₂, n = 3 (3); NCS, n = 0 (4), [MHLX] nH₂O, where M = Cu(II), X = OSO₃, n = 5 (5); M = VO(II), X = O₂SO₂, n = 2H₂O (6) and [UO₂L(ONO₂)(OH₂)₂].2H₂O (7). The X-ray diffraction (XRD) patterns of start 1, start 2, Schiff base and complex [Cu(L)₂] (1) are investigated in powder forms. The molecular and electronic structures of the ligand (HL) and its complexes have been discussed. It was found that form (A) is more stable than other forms (B and C). The HL ligand acts as a monobasic tridentate ONO donor for complexes (1–4 and 7) and neural tridentate HONO donor for complexes (5 and 6). The molar conductivity shows that the complexes are non-electrolytes nature. Electronic spectra and magnetic moments suggested varieties of geometries around the central metal atoms. The ESR spectra of complexes (2–4) show square planar of axial type symmetry (d_x2–y2) with considerable ionic bond character, while complex (1) shows a spectrum of octahedral geometry. The stability of these complexes has also been investigated. The ligand is designed as a building block for larger molecule and supramolecular assemblies. Schiff base of HL and complexes were tested against four local bacterial species; namely two Gram positive bacteria (Staphylococcus aureus and Bacillus cereus) and two Gram negative bacteria (Escherichia coli and Klebsiella pneumoniae) and against four local fungal species (Aspergillus niger, Fusarium oxysporium, Penicillium italicum and Alternaria alternata). 8-Hydroxy-7-formylquinoline and 4-amino-1-phenyl-2,3-dimethylpyrazolin-5-one showed antimicrobial activities against E. coli, K. pneumoniae, P. italicum and A. alternata. The inhibitive action of this Schiff base, against the corrosion of mild steel in 2 M HCl solution has been investigated using Tafel polarization and electrochemical impedance spectroscopy (EIS).