A complexation study of 15-crown-5 with Co2+ cation in some pure and mixed organic solvents

Abstract

The stability constant (log Kf) and the thermodynamic parameters (free energies, enthalpies, and entropies) of the complexation of Co2+ cation with 15-crown-5 (15C5) in acetonitrile-methanol (AN/MeOH), acetonitrile-nitrobenzene (AN/NB), acetonitrile-dichloromethane (AN/DCM) and acetonitrile-1,2-dichloroethane (AN/DCE) binary solvent solutions were calculated from the experimental conductance data at different temperatures. The complexation behavior of the crown ether used in these media was discussed in view of the estimated parameters. In all solvent systems, 15-crown-5 formed a 1: 1 complex with Co2+ cation. The stability order of (Co-15C5)2+ complex in the binary mixed solvents at 25°C was found to be: AN/NB > AN/DCM ≈ AN/DCE > AN/MeOH. In most cases, a non-linear relationship was observed for changes of log Kf of (Co-15C5)2+ complex versus the composition of the binary mixed solvent systems. The experimental results show that the standard thermodynamic parameters of the complexation process change with the nature and composition of the binary solvent solutions.