Stability constants and thermodynamic behaviour of the complex formation of two crown ethers with zinc (II) and copper (II) ions in water plus acetonitrile mixed solvent: a conductivity measurement study

We have investigated the behaviour of change of molar conductivity of mixtures of two crown ethers (CE) (18-Crown-6; 18C6 and 24-Crown-8; 24C8) and metal ions (Mn+) (Zn2+ and Cu2+) and the complexation between CE and Mn+ in water + acetonitrile binary solvent system (20, 40, 60 and 80%; v/v) at 298.15 K to 328.15 K by conductometric technique. K-f values for all complexes were found to be decreased with enhancement of temperature. Complexes associated with Zn2+ exhibit a trend of K-f: 24C8 + Zn2+ > 18C6 + Zn2+ in 20% solvent composition (water-acetonitrile) and order of 18C6 + Zn2+ > 24C8 + Zn2+ was found for 80% solvent composition. However, logarithm values of K-f for the Cu2+ complexes were found to obey the order of 24C8 > 18C6 almost for all compositions except with a few exceptions. Delta G(o) was found to be negative indicating spontaneous complexation between CE and Mn+.

Automated summary

The molar conductivity of mixtures of crown ethers and metal ions in a binary solvent system was investigated using conductometric technique. The K-f values of the complexes decreased with temperature increase, showing different stability trends for Zn2+ and Cu2+ complexes. The negative value of ΔG(o) indicated spontaneous complexation between the crown ethers and metal ions.