A Conductometric Study of Complexation Reactions between Kryptofix5 with Al3+, Fe3+, Cu2+, and Ca2+ Metal Cations in Acetonitrile–Ethanol Binary Solvent Solutions

Abstract

In the current study, the results of the conductometric work of the complexation reaction of Kryptofix5 (Scheme 1) with Al3+, Cu2+, Ca2+, and Fe3+ cations are studied in acetonitrile–ethanol (AN–EtOH) binary non-aqueous solvents. In all cases, the achieved results reveal that the stoichiometry of the complexes formed between the ligand and Al3+, Cu2+, Ca2+, and Fe3+ metal cations is 1 : 1 [ML] complex. GENPLOT (the computer program) calculates the stability constants of complexes of (Kryptofix5 · M)n+. The selectivity order of Kryptofix5 ligand for the studied metal cations in pure AN and AN–EtOH (AN = 50 mol % ) binary mixed solvent at 15°C is found to be Ca2+ > Fe3+ > Cu2+ > Al3+ and Cu2+ > Fe3+ > Ca2+ > Al3+, respectively. As a result, the selectivity order of the ligand for the metal cations shows independence from the nature and composition of the mixed binary solvent. By using the Van’t Hoff plots, the thermodynamic parameters ( $$\Delta H_{{\text{c}}}^{^\circ }$$ , $$\Delta S_{{\text{c}}}^{^\circ }$$ ) value for 1 : 1 complexes are calculated from the temperature due to the stability constants of the complexes. The achieved findings reveal that the thermodynamics of the complexation reaction is affected by the nature and composition of the mixed solvents, and the complexation processes entropy and enthalpy are stabilized in most cases.