Solution state studies on thermodynamic parameters and complexation behavior of inner transition metal ions with creatinine in aqueous and mixed equilibria

The determination of formation constants of binary inner transition metal complexes where M =Y(III) or La(III) or Ce(III) or Pr(III) or Nd(III) or Sm (III) or Gd (III) or Dy (III) or Th(IV) and L = Creatinine have been carried out using Irving–Rossotti titration technique in aqueous media at different temperatures and at ionic strength. To understand more about the nature of equilibrium involving inner transition metals with Creatinine, the effect of dielectric constants on the stability of these complexes at different percentage of solvent variation and at different solvent systems has been studied. The formation constant (logβn) have been calculated on IBM computer using BEST Program. Thermodynamic parameters (ΔG, ΔH and ΔS) are also evaluated, negative ΔG, ΔH and ΔS values indicate that complex formation is favorable at ordinary temperatures. Species distribution curves of complexes have been plotted as function of pH using Fortran IV program SPE PLOT to visualize the equilibria systems in pH range of 2-8 pH. The order of stability for metals is Y < La < Ce < Pr < Nd < Sm < Gd < Dy < Th. This order can be explained on the basis of basicity of ligand, protonation of ligand, electronic configuration of metal ions, size and ionic potential of tripositive ion, charge/size ratio of metal ions and species distribution diagrams.