Spectral, Thermal and Photocatalytic Properties of Transition Metal Complexes Based on a Ligand Derived from Gallic Acid and Ethylenediamine

A ligand, formed from the coupling of gallic acid with ethylenediamine, namely 3,4,5‐trihydroxy‐N‐{2‐[(3,4,5‐trihydroxyphenyl)formamido]ethyl}benzamide (GEtH₂), and its Cu(II), Ni(II) and Co(II) complexes, were synthesized. The corresponding structures were described by elemental analysis, infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis (TGA). The data revealed that GEtH₂ acts as a binegative tetradentate ligand via carbonyl oxygen atoms and deprotonated amide nitrogen. The paper discusses the thermal decomposition behavior of the prepared ligand and its complexes and evaluates the kinetic and thermodynamic parameters of the stage of decomposition using the Coats–Redfern method. The analysis studies of TGA data reflected potential and good thermal stability of GEtH₂ and its metal complexes. The photocatalytic performances of the complexes for the decomposition of methyl orange (MO) under ultraviolet irradiation were also investigated. The result showed that the degradation of MO after 150 min irradiation is 76.96, 85.55 and 71.86% for Cu(II), Ni(II) and Co(II) complexes, respectively.