Spectroscopic studies and determination of the formation constants and thermodynamic parameters for a new water-soluble Co(II) Schiff-base complex and some imidazole derivatives

Abstract

A new water-soluble Co(II) Schiff-base complex, sodium[{N,N′-bis(5-sulfosalicylidene)-1,8-diamino-3,6-dioxaoctan}cobalt] dihydrate, abbreviated as Na₂[Co(II)L], was synthesized and characterized. The formation constants and thermodynamic parameters for the interaction of this complex with imidazole (Im) and 1-methylimidazole (MeIm) were determined spectroscopically in aqueous solution, ethanol/water (10/90), and methanol/water (10/90) under physiological conditions (pH = 7), constant ionic strength (I = 0.1 mol dm⁻³ KNO₃), and various temperatures ranging from 294 to 310 K. Our spectroscopic and thermodynamic results show that this adduct formation is endothermic and the positive values of ΔS _f° make ΔG _f° negative. The trend in variation of ΔH _f° and ΔS _f° for Im is in the order water > methanol > ethanol, but for MeIm it is in the opposite order which is related to the hydrogen bonding between solvents and these donors. Formation constants between MeIm and Na₂[Co(II)L] in these three solvents are larger than for Im which depends on the electron donation of methyl on MeIm.

Keywords:

• Benesi–Hildebrand equation
• Formation constant
• Thermodynamic parameters
• Co(II) Schiff base

Acknowledgments

We would like to acknowledge financial support from the office of gifted students at Semnan University. We are also grateful to Dr N. Azizi and Mr Reza Valiollahi for their kind support and help during this work.