International Journal of New Chemistry
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Determination of Thermodynamic Stability of a Ni (II) Glycine Complexes in aqueous solution: Potentiometric and Spectroscopic Studies

Document Type : Research Paper

Authors

Fateh Eltaboni
Fatin Elmagbari
Ahmed Hammouda
Rashd El-Ferjani
Younis Ben Amer
Hamdi Bennour
Ali Alsaqir

Chemistry Department, Faculty of Science, University of Benghazi, Benghazi, Libya

https://doi.org/10.22034/ijnc.2023.1988465.1324
Abstract
The stability constants of Glycine and Ni(II)Glyx complexes (x = 0-3) in aqueous solution were studied by potentiometric titration at 25°C. The data analysis afforded insight on speciation, which was further confirmed by measuring absorbance in the UV-VIS region, covering a pH range from 2 to 11 to establish the Ni(II)Gly complex extinction coefficients. The potentiometric and spectroscopic data were analyzed using the computer program ESTA. It was shown that the formation of Ni(II)/glycinate complexes are strongly pH dependent. The Ni(II) competes with the protons bound to Glycine at the amine and carboxylate moiety. The successive formation of the NiL, NiL2 and NiL3 was observed as the pH was increased. Free Ni(II) complexes with one Glycine ligand above pH 4 followed by further association of another Glycine ligand above pH 6 and again at pH 8 to form the NiL3 complex. The stability of the complexes is proportional to the number of glycine ligands bound. The analysis of the spectroscopic data supports this trend as an increase in Glycine bound to the Ni(II) center. However, it increases its stability in need of shorter wavelength (higher energy) to excite the electron, suggesting stronger field splitting exerted by the glycine ligand due to higher stability. Thermodynamics study proposed that the increase in stability of the Ni(II) complexes was in this direction: NiL3 > NiL2 > NiL Good correspondence between theoretical and experimental data, low standard deviations in the stability constants and low RH lend reasonable confidence in all obtained results.

Keywords

Glycine
Ni(II) complexes
potentiometric
UV-VIS spectroscopy
Subjects
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International Journal of New Chemistry
Volume 10, Issue 4
Autumn 2023
Pages 223-235

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