Solvent Effect on Stability and Thermodynamic Behavior of Complex of 18-Crown-6 with Hydroxyl Ammonium Cation

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The complexation reaction between hydroxyl ammonium (HONH3+ ) cation with 18-crown-6 (18C6) ligand was studied in dimethylsulfoxide – water (DMSO-H2O), methanol – water (MeOH-H2O) and dimethylformamid – methanol (DMF-MeOH), binary solutions at different temperatures using conductometric method. The obtained results show that the stoichiometry of the complex formed between HONH3+ cation with (18C6 ) in all of the binary mixed solvents is 1:1[ML], as well as, these results show that the nature and the composition of the solvent systems are important factors that are effective on the stability of the complex formed between the macrocyclic ligand and metal cation in solutions. A non-linear behavior was observed for changes of stability constants of the complex versus the composition of the binary mixed solvents. The values of thermodynamic parameters show that  the  thermodynamics  of  complexation  reaction is affected by the nature and composition of the mixed solvents and the complex is entropy stabilized, but enthalpy destabilized in most compositions of binary solutions.