Preparation of a novel Mixed-Ligand divalent metal complexes from solvent free Synthesized Schiff base derived from 2,6-Diaminopyridine with cinnamaldehyde and 2,2′‐Bipyridine: Characterization and antibacterial activities

Abstract

The solvent-free conditions were employed to synthesise symmetrical Schiff base ligand from 2,6-diaminopyridine with cinnamaldehyde in (1 min) with a fair yield utilizing formic acid as a catalyst. Through coordination chemistry, new heteroleptic complexes of Cu(II), Co(II), Ni(II), Pt(II), Pd(II) and Zn(II) were achieved from Schiff base as a primary chelator (L 1 ) and 2,2′‐bipyridine (2,2′-bipy) as a secondary chelator (L 2 ). The prepared compounds have been characterized by elemental analysis, molar conductivity, magnetic susceptibility, FTIR, 1 H NMR, UV–visible, mass spectrometry, and thermal gravimetric analysis, and screened in vitro for their potential as antibacterial activity by the agar well diffusion method. The metal complexes were formulated as [M (L 1 ) (L 2 ) (X)] Y ⋅ nH 2 O, L 1 = Schiff base, L 2 = 2,2′-bipy, (M = Cu(II), Co(II), Zn(II), Y = 2NO 3 , n = 1), (M = Ni(II), X = 2H 2 O, Y = 2NO 3, n = 0) and (M = Pd(II) Pt(II), Y = 2Cl, n = 0). Both L 1 and L 2 act as a neutral bidentate ligand and coordinates via nitrogen atoms of imine and 2,2′-bipy to metal ions. The metal complexes were found to be electrolytic, with square-planar heteroleptic Cu(II), Co(II), Pt(II), and Pd(II) chelates and octahedral Ni(II) complex. As well as tetrahedral geometry, has been proposed for the complex of Zn(II). Furthermore, the biological activity study revealed that some metal chelates have excellent activity than Schiff base when tested against Gram-negative and Gram-positive strains of Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ). Finally, it was found that the Zn(II) and Pd(II) complexes were more effective against both types of bacteria tested than the imine and other metal complexes.