A Solution State Study of the Complexation and Thermodynamic Parameters of Binary Complexes of the Inner Transition Metals with Piracetam in Aqueous and Mixed Solvents

An equilibrium study on complexation behavior of the inner transition metals, where M = {Y(III), La(III, Ce(III, Pr(III), Nd(III), Sm(III), Gd(III), Dy(III), Th(IV)} and L = piracetam, has been carried out using the Irving–Rossotti titration technique in aqueous media at different temperatures and ionic strengths. The protonation constant and stability constants (log₁₀ β _n ) of the resulting inner metal–ligand complexes have been calculated with the Fortran IV program BEST using the method of least squares and considering the BESTFIT model. Thermodynamic parameters were also evaluated, yielding negative ΔG°, ΔH° and positive ΔS° values that indicate complex formation is favorable at ordinary temperatures. Species distribution curves of complexes have been plotted as function of pH using the SPEPLOT FORTRAN IV program to visualize the presence of various species in equilibrium in the pH range 2–6. To understand more about these equilibria, the stability of these complexes was studied at different percentages of solvent (10–30 % v/v) in different aqua-organic solvent mixtures with methanol, ethanol, 1-butanol and dimethylformamide.