Synthesis characterisation, thermal study and biological activity of a new azo-Schiff base ligand with some of its metal complexes

Synthesis characterisation, thermal study and biological activity of a new azo-Schiff base ligand with some of its metal complexesAbstract. This work reports the formation of a new type of azo-Schiff base ligand obtained from a 4-aminoantipyrine compound, together with its metal complexes. The ligand, 4-(((E)-(2-hydroxy-3-((E)-(4-nitrophenyl)diazenyl)- naphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL), was synthesised through the condensation reaction of (E)-2-hydroxy-3-((4-nitrophenyl)diazenyl)-1-naphthaldehyde with 4-aminoantipyrine in a molar ratio of 1:1. Coordination with Cr(III), Mn(II), Co(II), Ni(II), and Cu(II) chlorides in a 2:1 ligand to metal ratio afforded the corresponding complexes. These compounds (HL and complexes) were examined using spectroscopic and analytical techniques covering NMR (1H and 13C), FT-IR, UV-Visible, and mass spectroscopy, elemental microanalysis, magnetic susceptibility, and molar conductivity measurements. The spectroscopic and analytical results verified the structures of HL and its complexes, which generally exhibited six-coordinate geometries, except for the Ni(II) complex, which indicated a four-coordinate geometry. The thermal properties of the ligand (HL) and chosen coordination complexes were studied by thermogravimetric analysis (TGA). The antimicrobial evaluation of the synthesised compounds (HL and its coordination compounds against pathogens (bacterial and fungal species) indicated that the complexes displayed improved activity, related to the ligand. Specifically, the activity of metal complexes against the fungal species Candida albicans surpassed the activity of the reference drug fluconazole.Keywords: Azo-Schiff base ligand, Metal complexes, characterisation; Thermal properties, Antimicrobial activity.