Synthesis and characterization of Cu(II), Zn(II), Cd(II), and Mn(II) Complexes with heterocyclic N-donor ligands and carboxylic acid derivatives and their antibacterial activity

Abstract

This of a novel series of eight heteroleptic coordination complexes (1E-8E) incorporating carboxylate-based ligands (mefenanmic acid, para-toluic acid, meta-toluic acid,, and salicylic acid) and heterocyclic nitrogen-donor co-ligands (1, 10-phenanthroline, diphenyl-2-pyyridylphosphine study presents the synthesis, spectroscopic characterization, and preliminary biological evaluation, and 2-amino-5-methylthiazole) with divalent metals ions (Cu(II), Zn(II), Cd(II), and Mn(II)). Yhe metal complexes were synthesized vis salt metathesis reactions in methanolic media and characterized by using FTIR, and UV –Vis spectroscopy. FTIR analysis confirmed the bidentate coordination mode of the carboxylate ligands to the metal center, as evidenced by the separation values (Δν) between the asymmetric and symmetric COO stretching bands, which ranged from 34 to 105 cm^-1. Electronic absorption studies showed d-d transitions and ligand-to-metal charge transfer, with molar absorptivity (ε) values ranging from 13,333 to 16,666 L mol⁻¹ cm⁻¹, indicating a tetrahedral shape for the produced complexes. Additionally, the antibacterial activity of certain complexes (1E–4E) was evaluated against Gram-positive bacteria (B. subtilis and S. aureus), showing a dose-dependent increase in the zone of inhibition, underscoring their potential as antibacterial agents. The results highlight the effectiveness of carboxylate and N-donor ligand combinations in adjusting the structural, electrical, and functional characteristics of metal complexes, offering important new information to the field of supramolecular coordination chemistry.