Equilibrium Studies of Dibutyltin(IV)-Zwitterionic Buffer Complexation.

Equilibrium studies in aqueous solution are reported for dibutyltin(IV) (DBT) complexes of the zwitterionic buffers "Good's buffers" Mes and Mops. Stoichiometric and formation constants of the complexes formed were determined at different temperatures and ionic strength 0.1 mol·L-1 NaNO3. The results show that the best fit of the titration curves were obtained when the complexes ML, MLH-1, MLH-2 and MLH-3 were considered beside the hydrolysis product of the dibutyltin(IV) cation. The thermodynamic parameters ΔHo, ΔSo and ΔGo calculated from the temperature dependence of the formation constant of the dibutyltin(IV) complexes with 2-(N-morpholino)ethanesulfonic acid (Mes) and 3-(N-mor-pholino)-propanesulfonic acid (Mops) were investigated. The effect of dioxane as a solvent on the formation constants of DBT-Mes and DBT-Mops complexes decrease linearly with the increase of dioxane proportion in the medium. The concentration distribution of the various complexes species was evaluated as a function of pH.