Complexation of manganese(II), cobalt(II), nickel(II) and copper(II) by a ligand derived from 1,2,4-triazole: Potentiometric studies and Density Functional Theory calculations

DFT calculations have been conducted to understand the conformational and tautomeric preference of 4-amino-5-(2-hydroyphenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione ligand. The results suggest that the thione tautomer is found to be the most stable form in the gas phase, which is in very good agreement with the FT-IR and crystallographic data. The protonation constants of the ligand and the stability constants of its complexes with Mn(II), Co(II), Ni(II) and Cu(II) have been determined by potentiometry in water-ethanol (90:10, v:v) mixture. The absolute pKa values of the ligand have been calculated using DFT method to complement and help the assignment of potentiometric data. DFT calculations have also been carried out for some metallic complexes species formed in solution in order to propose their most probable structures

Copper(II) and nickel(II) complexes derived from a carbothioamide-5-pyrazolone ligand: synthesis, characterization, crystal structures, electrochemical, potentiometric and DNA-binding studies

International audienceThe synthesis of a 5-pyrazolone derivative (H2L) bearing a carbothioamide group at N1, N-ethyl-4-(2-hydroxyethyl)-3-methyl-5-oxo-2,5-dihydro-1H-pyrazole-1-carbothioamide, using a Keggin catalyst (H4SiW12O14·nH2O), is described. Complexes of copper(II) and nickel(II) have been prepared with this potential ligand and studied by potentiometry. Processing the pH-metric titrations revealed remarkable chelation ability of the ligand and high stability constants for the complexes. The complexes have been characterized by IR, UV/visible, electrochemistry, magnetic measurements, Electron Paramagnetic Resonance (EPR) and single-crystal X-ray diffraction. The structures are [Cu(HL)2H2O]·2H2O and [Ni(HL)2H2O]·2H2O, where the metal is five coordinate in an almost perfect trigonal bipyramidal geometry (D3h). The pyrazolone derivative (H2L) is a NS bidentate negative ligand, which coordinates to the metal through sulfur and amine nitrogen of the pyrazolone ring. The electronic results and the EPR of the complexes have been carefully studied in this (D3h) crystal field with a special emphasis on the energy levels. DNA-binding experiments have been conducted by UV spectroscopy and electrochemistry. The results reveal an interaction between the complexes and DNA and suggest an intercalative binding mode. UV titrations allowed determination of the binding constants Kb and revealed that the nickel(II) complex binds more strongl