Synthesis, characterization, DFT molecular modeling and biological studies of Zn(II), Cd(II) and Hg(II) complexes of new polydentate thiosemicarbazide

The new ligand, 2,2'-(9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbonyl)bis(N-ethyl hydrazine-1-carbothioamide) (H6ETS) and its complexes with Zn(II), Cd(II) and Hg(II) were synthesized and characterized using physicochemical techniques. The IR and H-1-NMR spectral data of the ligand indicated that it exists in two forms, keto- and enol-thione. The metal complexes spectral data revealed that in Zn(II) complex, the ligand acts as binegative hexadentate, while in the Hg(II) complex, it reacted in binegative tetradentate fashion. Moreover, the ligand chelated to the Cd(II) ion in neutral bidentate manner through the carbonyl and (NH)-H-2 groups. The thermogravimetric analyses of Cd(II) complex confirmed the absence of the water molecules outside or inside the coordination sphere. Furthermore, the thermodynamic parameters were evaluated using Coats-Redfern and Horowitz-Metzger methods. The bond lengths and angles for the ligand and its Cd (II) complex were calculated at Density Function Theory "DFT" level and showed very good agreement with the x-ray values of analogue compounds. The optical energy gap were calculated and compared with DFT estimated. The isolated compounds were examined to explore their antibacterial, DNA cleavage, superoxide dismutase (SOD) scavenging and hydroxyl radicals scavenging activities. (C) 2018 Elsevier B.V. All rights reserved.