Conductometric Study of Complexation of Macrocyclic Compounds with Zinc(II) and Copper(II) Ions in Aqueous-Organic Solvent Mixtures

The conductance behavior of Zn2+ and Cu2+ and their complexes with two ligands (crown ethers) have been inspected in 10, 20, 30, and 40% DMF–water mixed solvent at 298.15, 308.15, 318.15, and 328.15 K. The conductance study indicates a 1 : 1 complexation mode amongst the metal ions and ligands hereby studied. The order of stability constants with crown ethers was found to be Cu(II) > Zn(II). The stability constant for Zn2+ ion with crown ether complexes in 10 and 40 wt % solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5. The stability constant for Cu2+ ion with crown ether complexes in 10% solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5, and for 40% solvent composition, it is benzo-18-crown-6 > benzo-15-crown-5. The enthalpy and the entropy of complexation were estimated from the variation of stability constants with respect to the variation of temperature. The observed results elicit that the complexation is enthalpy stabilized, but entropy destabilized.