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Conductometric, spectrophotometric, 1HNMR and quantum chemical studies of the thermodynamics complexation of some transition metal ions with aza-15-crown-5 ligands in acetonitrile solution

Mahmood Payehghadr, Farzaneh Nourifard, Mehdi Taghdiri, Reza Behjatmanesh-Ardakani

In this paper, the complexation reactions between aza-15-crown-5 (A15C5) ligand with Zn2+, Hg2+, Co2+, Ag+ and Cd2+ ions has been studied by conductometric and spectrophotometric methods in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were calculated fromthe computer fitting of the molar conductancemole ratio data at different temperatures. At 25ºC, the order of stability of the 1:1 complexes of theA15C5 ligand with different cations are as Hg2+> Co2+> Cd2+> Zn2+>Ag+.The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. In addition, 1HNMR study of complexes of nitrate salt of Cd+2 in acetonitrile withA15C5 ligand at 25ï‚°C has been also undertaken to compare the results with those obtained by conductivity and UV measurements, which have been found to be in good agreement with each other. Finally, ab initio studies of the level of HF/lanl2dz have been done to investigate the binding energies of the ligand with Ag+ and Hg2+. All theoretical data are in line with the experimental ones.