Synthesis, Structural Investigation and Biological Activity of a Heterocyclic Schiff-Base Ligand and Its Coordination Complexes

This study reports the formation, characterisation and biological evaluation of a Schiff base ligand and its corresponding metal complexes. The Schiff base ligand (HL) was prepared through a condensation reaction involving isonicotinohydrazide and N'-((1R,2R,4R,5S, E)-2,4-bis(4-chlorophenyl)-3-azabi cyclo[3.3.1]nonan-9-ylidene) isonicotinohydrazide (M) in EtOH solvent and (3-5) drops of conc. HCl. The interaction of HL with selected metal chlorides including Mn(+2), Co(+2), Ni(+2), Cu(+2) and Zn(+2) in a 2:1 (L:M) mole ratio resulted in the synthesis of complexes with the general formula [M(HL)Cl2] (where: M = Mn(+2),Co(+2) and Ni(+2)) and [M`(HL)Cl2] (where M` = Cu(+2) and Zn(+2)). The characterisation of the prepared compounds was carried out using a range of spectroscopic analyses, containing FT-IR and electronic spectroscopy, NMR (1H and 13C), mass spectrometry, atomic absorption, as well as a range of analytical techniques to fully characterise the title compounds, including elemental microanalysis (C.H.N) for elemental composition determination, chloride percentage analysis, conductivity measurements to assess electrical conductivity in solution, magnetic moments to investigate the magnetic properties and melting point determination. These spectroscopic and analytical techniques were involved in validating the identity and structural properties of both the ligand and its corresponding coordination compounds. Besides the structural characterisation, the biological evaluation of the synthesised compounds toward both G+ and G- bacterial strains was assessed. This investigation sheds light on the potential applications of these compounds in combating bacterial infections.