Synthesis, characterization, and biological studies of novel Ni(II) and Zn(II) complexes with 5-chloro-2-(phenylazo)pyridine

Abstract

An azoimine compound, 5-chloro-2-(phenylazo)pyridine (Clazpy), reacted with Ni(II) and Zn(II) sulphate salts and formed divalent metal complexes with a general formula of [M(Clazpy)2(NCS)2], where M is Ni(II) or Zn(II). The synthesized complexes were characterized on the basis of elemental analysis, nuclear magnetic resonance, and infrared and electronic absorption spectroscopy. The single crystal X-ray diffraction and infrared data of the Zn(II) complex show that the ligand coordinates through the donating nitrogen atoms of the pyridine ring and azo moiety of Clazpy and N atoms of the thiocyanate groups. Our density functional theory calculations used the B3LYP/6-31G(d,p)&LANL2DZ functional and basis sets to predict the most favourable structures of [Ni(Clazpy)2 (NCS)2] and [Zn(Clazpy)2(NCS)2]. The TD-CAM-B3LYP/6-31+G(d,p)&LANL2DZ electronic transition energies agree with the electronic spectra and hence confirm their structures. Minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations or minimal fungicidal concentrations (MFC) of all tested compounds were determined against human pathogens by a colorimetric microdilution method. The Clazpy compound and its complexes are significantly active against yeast and filamentous fungus with MIC and MFC values of 32 and 200 μg/ml, respectively. The Clazpy ligand showed higher antimicrobial activities against pathogenic yeast Cryptococcus neoformans (MIC/MFC 32/32 μg/ml) than both complexes (MIC/MFC 64/128 μg/ml). The [Ni(Clazpy)2(NCS)2] complex exhibited higher antimicrobial activities against fungal strains of Microsporum gypseum (MIC/MFC 64/128 μg/ml) than the [Zn(Clazpy)2 (NCS)2] complex. These new azoimine metal complexes might therefore beconsidered as prospective antifungal agents.