Complexes formed by a heterocyclic schiff base containing an aminothiophene group with Ni(II) and Co(II) metals and their structural characterization

In this study, compound 2, a novel Schiff base ligand containing an aminothiophene group, was synthesized and thoroughly characterized. The amine precursor (1) was condensed with 5-chloro-2-hydroxybenzaldehyde to yield the target ligand in high yield (90%). The ligand's structure was confirmed using FT-IR, 1H NMR, 13C-APT NMR, LC-MS (-ESI), and elemental analysis. The crystallographic study revealed that the ligand is arranged in the triclinic P & imath; space group, with two molecules present in each unit cell. The measured C7-N1 and C10-O2 bond lengths exhibit double-bond character, and the phenyl-thiophene dihedral angle of 6.02 degrees points to an almost planar structure. A hydrogen bond formed within the molecule between the phenolic-OH and imine nitrogen, and pi & sdot;& sdot;& sdot;pi interactions between adjacent molecules enhanced crystal stability. The ligand reacted with Co2+ and Ni2+ salts under reflux conditions to afford the corresponding metal complexes (3 and 4). Analysis by FT-IR revealed that the phenolic-OH band vanished, while the C = O and imine (C = N) groups participated in coordination. The imine stretching shift indicated nitrogen coordination, and the additional bands in the 655-531 cm-1 region verified metal-oxygen interactions. Elemental analyses matched the proposed molecular formulas, and magnetic susceptibility measurements indicated octahedral Co2+ and Ni2+ centres with paramagnetic properties. Thermal analyses revealed a multi-step decomposition process, ultimately yielding metal oxides (CoO, NiO) as the final residues. This study demonstrates that the Schiff base ligand acts as a bidentate (O, N) chelating agent, forming stable metal complexes. The ligand and its complexes, due to the imine group, thiophene ring, and heterocyclic structure, offer potential antimicrobial, anticancer, antioxidant, and sensor applications. These results underscore the role of Schiff bases and transition metal complexes in catalysis, materials science, and bioinorganic applications.