The complexation reaction between Y3+ cation with macrocyclic ligand dibenzo-18-crown-6 (DB18C6), was studied in pure acetonitrile (AN), dimethylformamide (DMF), methanol (MeOH), ethanol (EtOH) and propanol (PrOH) and acetonitriledimethylformamide (AN-DMF), dimethylformamide-methanol (DMF-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-propanol (AN-PrOH) binary mixtures at different temperatures using coductometry method. The conductometric technique is highly sensitive and inexpensive[1]. The experimental procedure as follows: the conductance of a solution of metal salt(110-4M) was measured, then a step-by-step increase in the crown ether concentration was performed by a rapid transfer from crown ether solution in the same solvent(210-3M) to the titration cell. In all cases, DB18C6 forms a 1:1complex with Y3+cation. Addition of DB18C6 to the solution of Y3+ cation, in all cases shows a continuous increase in the molar conductivity of the solutions indicating the higher mobility of the complexed cation compared to the uncomplexed one. The stability constants of the complex at each temperature was calculated from variation of molar conductance as a function of ligand/metal cation mole ratios using a GENPLOT computer program[2]. A non-linear behaviour was observed between logKf of the complex versus the composition of the mixed solvents which may be related to the solvent-solvent interactions which result in changing the solvation of the metal cation, ligand and even the resulting complex in the binary mixed solvents[3]. The order of the stability constant of (DB18C6.Y)3+ complex in pure non-aqueous solvents is: AN>DMF(the ligand is not dissolved in pure MeOH, EtOH and PrOH). The stability constant of (DB18C6.Y)3+ complex in the binary mixed solvents at 15̊Cand 25̊C,varies in order: AN-EtOH>AN-PrOH>AN-DMF, but at 35̊Cchanges to: AN-PrOH>AN-EtOH>AN-DMF and at 45̊C it varies to: AN-EtOH>ANDMF>AN-PrOH. The values of thermodynamic parameters(ΔS°c,ΔH°c) for formation of (DB18C6.Y)3+ complex were obtained from temperature dependence of the formation constant of the complex using the van\\\'t Hoff plots[4]. The obtained results show that in most caseses, the complextion reaction between is entropy stabilized, but from enthalpy weiv point, there is not a regular trend of this thermodynamic parameter with the nature of the medium.

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