Conductometric Investigation of Schiff Bases and Ni(II) Ions: Stability and Thermodynamics in Nonaqueous Solutions

This research explores the synthesis and characterization of two Schiff bases, L۱ and L۲, and their complexation with Ni(II) ions in non-aqueous solvents, providing insights into the stability and thermodynamic properties of the resulting complexes. L۱ was synthesized by condensing o-hydroxyacetophenone and salicylaldehyde with ethylenediamine, while L۲ was derived from ۲,۳-dihydroxybenzaldehyde and ethylenediamine. Conductometric titrations were performed using a Jenway ۴۵۱۰ conductometer equipped with a Julabo ED circulator for precise temperature control. Measurements were conducted in absolute ethanol, acetonitrile, and a ۱:۱ (v/v) ethanol/acetonitrile mixture across a temperature range of ۲۵–۴۰°C (increments of ۵°C). The conductance was recorded after sequential additions of of ligand solution to ۲۰.۰ mL of Ni(II) solution until the molar ratio [L]/[M] reached ۱۰:۱. Stability constants were derived from the resulting conductance-mole ratio plots. The results demonstrate that the stability constants decrease with increasing temperature, confirming the exothermic nature of the reactions. The stability order of the complexes across the solvents was acetonitrile > mixture > ethanol, reflecting the influence of solvent properties. Additionally, L۲ complexes exhibited higher stability than those of L۱, attributed to the enhanced Lewis basicity conferred by its hydroxyl groups, while the methyl group in L۱ introduced steric hindrance, reducing stability. Thermodynamic analysis revealed negative ∆Ho (from -۶.۶۰ kJ/mol to -۱۹۶ kJ/mol) and ∆Go (from -۲۷.۱ kJ/mol to ۳۶.۸ kJ/mol), indicating exothermic and spontaneous reactions. Entropy changes ∆So varied slightly between solvents, reflecting differences in molecular interactions. This study highlights the influence of ligand structure, solvent properties, and temperature on complexation stability and provides a detailed thermodynamic perspective. These findings contribute to the understanding of metal-ligand interactions, offering potential applications in designing coordination compounds for chemical and industrial processes.

کلیدواژه ها:

Conductometry ، Schiff bases ، Stability Constants ، Nonaqueous solutions ، Thermodynamic analysis