Determination of stability constant, thermodynamic parameters and stoichiometry of complex formation between 1, 8-dihydroxyanthraquinone(DHAQ) and 1-(methylamino) anthraquinone(MAAQ) with Cu2+, Zn2+ and Ag+ cations in acetonitrile(AN)- methanol(MeOH) binary mixtures

In this study, the complexation reaction between Cu2, Zn2 and Ag cations with 1,8-dihydroxyanthraquinone (DHAQ) and 1- (methylamino) anthraquinone (MAAQ) was studied in (AN/MeOH) binary mixtures at different temperatures using conductometry method. The conductivity data indicates in all cases, the stoichiometry of the complexes is [ML]1:1 except for the complex formation reaction between Cu2 cation and DHAQ ligand in pure methanol and in AN/MeOH (mol% AN = 75) binary solutions was obtained [M2L] 2:1. The stability constants of complexes were calculated using Genplot software and non–linear fitting of conductometric data. Also, the experimental data show that the selectivity order of DHAQ and MAAQ for Cu2, Zn2 and Ag cations, in addition to the ligand, changes with mole fraction of a component of the solvent in AN/MeOH binary mixtures. The value of &DeltaHºc for formation of complexes was obtained from temperature dependence of the stability constants of the complexes using the Vant Hoff plots and linear fitting using mentioned software. The results showed the complexation reaction between Cu2, Zn2 and Ag cations with DHAQ and MAAQ in this binary mixtures are endothermic and, in all cases the resulting complexes are entropy stabilized but enthalpy destabilized. Also, the T&DeltaSºc versus &DeltaHºc plot of all thermodynamic data indicated a fairly good linear correlation indicating the existence of the enthalpy– entropy compensation in the complexation reactions.