A Study of Metal Complexes: Synthesis, Characterisation, and Applications of Selected Divalent Transition-Metal β-Diketonate Chelates

Abstract

Metal complexes derived from β-diketone ligands occupy a central place in modern coordination chemistry because a single, easily prepared ligand framework can accommodate a range of transition-metal ions and yield complexes whose structure and function can be tuned by the choice of metal centre. The present study reports the synthesis, characterisation, and evaluation of four divalent transition-metal complexes of a 1,3-diketone (β-diketone) ligand, HDKN, prepared under a common protocol so that observed differences across the series could be attributed to the intrinsic chemistry of the metal ions rather than to variations in preparative method. The ligand was condensed and purified by recrystallisation, and its complexes with copper(II), nickel(II), cobalt(II), and zinc(II) were obtained in moderate to good yield (69–78%) by refluxing a 2:1 ligand-to-metal mixture under mildly basic conditions. The complexes were characterised by elemental (CHN) analysis, molar conductance, magnetic-susceptibility measurements, UV–visible, FTIR, ¹H NMR, and mass spectrometry, and their thermal behaviour was examined by thermogravimetric and differential thermal analysis. Low molar conductance values (8–12 Ω⁻¹ cm² mol⁻¹) confirmed that all four complexes are non-electrolytes, and magnetic moments (1.78, 2.95, and 4.10 B.M. for the copper, nickel, and cobalt complexes, with the zinc complex diamagnetic) together with electronic spectra established square-planar, octahedral, octahedral, and tetrahedral geometries, respectively. Infrared data confirmed that HDKN binds as a mono-anionic, bidentate O,O-donor through the enolate and carbonyl oxygens. The complexes were screened for catalytic (oxidation), antibacterial, antifungal, antioxidant, anticancer, and environmental (dye-degradation and heavy-metal-adsorption) activity. The copper (II) complex was consistently the most active across all functional assays, a result attributed to its accessible Cu(II)/Cu(I) redox couple, favourable lipophilicity, and coordinatively accessible geometry. The study establishes clear structure–property and structure–activity relationships governed principally by the identity of the metal centre and demonstrates the multifunctional potential of first-row transition-metal β-diketonate chelates.